CH 390

9. Which vibration in CO2 is has the biggest warming effect on the atmosphere? Why?

~ 15.0 um (freq. ~ 2 x 10^13 cycles per second (Hertz) for *bending* ~ 4.26 for antisymmetric stretch Here because the absorption matches the frequency of the OCO *angle-bending* vibration of CO2 - one of the ranges of maximum absorption - it's here that IR thermal light can be absorbed and re-emitted the most (absorbs around 50% of light in 15 um zone) - dipoles no longer cancel (not pulling opposite of each other) = polar molecule

3. What happens to the sunlight that comes into the Earth's atmosphere? What molecules are primarily responsible for absorbing UV and IR wavelengths of light? (these statistics were in lecture)

~ 50% is absorbed by water bodies, soil, vegetation, buildings, etc additional 20% absorbed by water droplets in air and molecular gases - UV by stratospheric ozone + O2 - IR by CO2 + water vapor ^ heats earth/atmosphere ------------- ~ 30% reflected back to space by cloud, suspended particles, ice, snow, sand, and other reflective bodies

5. In general, how does the energy required to drive a dissociation reaction compare with the enthalpy of that reaction?

ΔH° equals energy required to drive the reaction - E supplied by oen photon per molecule Can calculate by switching E = (hc)/λ rxn to: λ = (hc)/E

6. What is atom economy? How is it calculated?

*Atom economy* - Measure of what mass of atoms in reactants are incorporated into final desired product - How efficiently atoms in reactants are used/ how well the synthesis does it % Atom economy = (molar mass of desired product(s) / total molar mass of reactants) *100%

2. What is blackbody radiation? How can the wavelength maximum of a radiating blackbody be calculated from its temperature? Why does the Earth radiate at a much longer wavelength than the sun?

*Blackbody* = an object that is 100% efficient in absorbing radiation - emits radiation based only on temperature --------- Can be calculated from temperature by using: (peak wavelength) = 2897/T T = temp in kelvins Since max emission decreases inversely with increasing K temp (aka higher energy) ------------ Earth radiation has a longer wavelength because the earth's temperature is much lower than the sun - bc of this, sun emits UV, visible, and IR radiation > while earth only emits thermal IR > sun radiation peaks at visible

13. What is geoengineering? What two general categories of geoengineering are being investigated to mitigate global warming?

*Geoengineering* - massive-scale schemes that intentionally attempt to alter the climate of the entire planet - usually by lowering air temp Two general categories: 1) *reflecting* a small fraction of sunlight approaching earth back to space - reducing amount of sunlight absorbed / converted to heat - *Solar radiation management* (SRM) methods all involve the placement of reflecting microscopic particles/macroscopic objects high in the sky - Advantage over CO2 is that *their effect would occur more quickly* (~years) 2) *removing* carbon dioxide from ambient air and storing it

11. What is the greenhouse effect? Is this a new phenomenon? What effect does it have on the Earth?

*Greenhouse effect* - Phenomenon of interception of outgoing IR by atmospheric constituents + its dissipation as heat to increase temp of atmosphere It isn't new - it maintains the average temperature of the Earth's surface adn air close to it at ~15 degrees C rather than negative 18 degrees C Changes temperature of localized air

8. What are HFCs? Why are these preferable to HCFCs? What are the environmental risks associated with use of these compounds?

*Hydrofluorocarbons* (HFCs) - substances that contain hydrogen, fluorine, and carbon, but NO chlorine Preferable because they won't destroy stratospheric ozone Environmental risks 1) MAkes *trifluoroacetic acid* (TFA), which may accumulate in aquatic plants + wetlands 2) Accumulates in air during use, contributing to global warming - greenhouse gas

17. What are the catalytically inactive molecules that normally contain a majority of the chlorine in the stratosphere? What are the reactions leading to the formation of these molecules?

*Hydrogen chloride* gas (HCl) and *Chlorine nitrate* gas (ClONO2) - "reservoir molecules" ---------------- ClO + NO2 + <> ClONO2 sun ---- Cl + CH4 (methane) > HCl + CH3 - slow rate OH (hydroxyl) + HCl > H2O + Cl

16. What is a PM index? What do the subscripts next to the PM in the measured values mean?

*PM index* - amount of particulate matter that is present in a given volume - matter not homogenous = molar mass not used. Concentration give in mass - usual unit = micrograms of particulate matter per cubic meter of air (ug/m^3) Only particles having a specific diameter or less are collected/reported (bc smaller particles are worse for human health) - *this diameter is indicated by a subscript* Many places use PM10 (total concentration of all particles having diameters less than 10 um) - whole of fine particle range + some coarse - known as *inhalable* particles bc they can be breathed into lungs More commonly people use *PM2.5* - only and all fine (*respirable*) particles - can penetrate deep into lungs - ex. carbon, VOCs, sulfates

10. How can particulates suspended in air be classified? What is an aerosol?

*Particulates* - tiny solid or liquid particles (other than pure H2O) that are temporarily suspended in air - usually invisible to naked eye - together form a haze - breathing them in is hazardous - variable in size and composition --------------- Classified as *coarse* or *fine* based on diameter (greater or less than 2.5 um) --------------- Aerosol is a collection of particulates, solid or liquid, dispersed in air - contains very small particles (diameters less than 100 um)

4. What is albedo? Why is it important to the total energy absorbed by the Earth?

*albedo* is the fraction of sunlight reflected back into space by an object - how much light is reflected - lighter tend to have higher albedo It is important because this reduces the total energy absorbed (possibly contributing to global warming)

5. What are the clean coal technologies: combustion cleaning - how do they work?

*combustion cleaning* - Combustion process modified to produce less pollutants, or pollutant-absorbing substances added to fuel to absorb pollutants as they form *fluidized-bed combustion* - Pulverized coal + limestone (CaCO3) are mixed and suspended on jets of air - ~Half of sulfur dioxide is captured in solid calcium sulfite and sulfate - Allows for reduced combustion temps too, reducing amount of nitrogen oxides formed - Not often used bc capture efficiency not high enough for standards

5. What species initiates the first reaction in the oxidation of many trace gases? How is this species formed? How long does this species last in the troposphere?

*hydroxyl free radical* (OH) initiates the reaction (NOT O2) OH formed by: - When excited oxygen atoms resulting from photochemical decomposition of ozone reacts w/ water (g) to take one h atom from each H2O molecule O3 + UV-B > O2 + O* O* + H2O > 2OH ------------------- OH lasts for around one second, due to high reactivity (free radical) Concentration drops off at night, bc need light to form

11. What molecule is primarily responsible for filtering out UV light in the 220-320 nm range?

*ozone* (O3) is mainly responsible Less efficient absorbance in 290-320

5. What are the clean coal technologies: postcombustion cleaning, and how do they work?

*postcombustion cleaning* Granular calcium oxide, calcium carbonate, or sodium sulfite solutions described previously - flue-gas desulfurization *SNOX* - cooled flue gases mixed w/ ammonia gas to remove nitric oxide (NO2) via catalytic reduction to molecular nitrogen (N2) (see section 3.13) - resulting gas reheated, sulfur dioxide (SO2) oxidized catalytically to sulfur trioxide (SO3) . Hydrated to sulfuric acid (H2SO4), condensed, and removed ----------------- separate thing? *coal conversion* - Fuel gasified w/ steam - Gas mix is cleaned of pollutants. Purified gast then burned in gas turbine, generating electricity - waste heat used to produce steam, powering a normal turbine and make mroe electricity - gasified coal can also be converted to liquid fuel for use *coal conversion* Lecture: 1) Pretreatment - aids gasification process 2) raw gas cleaning - removes ash/tar/acid gas 3) Beneficiation - improves fuel characteristics

5. What are the clean coal technologies: precombustion cleaning, and how do they work?

*precombustion cleaning* - Some sulfur in the mineral removed (usually pyritic sulfur (FeS2) before burning - Prevents it from making sulfur dioxide 1) Physically - Coal ground up to fine particle size (separating mineral and carbon particles) - both put into water, and separate by density - mineral floats to top, and can be skimmed off - doesn't remove organic sulfur v these two remove organic sulfur Alt 2) biological - bacteria cultured to eat organic sulfur in coal can be used Alt 3) chemical - sulfur can be leached from coal using hot sodium or potassium caustic solution

6. What is the difference between a symmetric stretch and an asymmetric stretch? Which type of stretching leads to the IR absorption of CO2?

*symmetric stretch* - synchronized movements of molecules (i.e. expansion and expansion) - dipole moments still cancel *asymmetric stretch* - asynchronous movements of molecules (ex. contraction vs. expansion) - This leads to IR absorption of CO2 > molecular polarity changes

2. What types of motions correspond to the frequency of an IR photon?

*vibrations* are in the IR region

15. Why is the presence of chlorine-containing gases in the atmosphere an environmental concern? What major environmental issue has the increase in these gases led to? What are the natural sources of chlorine-containing gases?

- Cl is a free radical + efficient x catalyst - Gases containing chlorine are also stable enough to get to stratosphere, where the chlorine is released -------------- Mainly led to *Ozone hole* -------------- Methyl chloride gas (CH3Cl) - Comes from ocean chloride interactions w/ vegetation - Also from tropical plants

How can N2O arise from both nitrification and denitrification processes?

- denitrification in aerobic (oxygen rich) environments - nitrification process in anaerobic (O-poor) environments Denitrification -fully oxidized nitrogen in *nitrate ion (NO3-)* is reduced mostly to molecular *nitrogen (N2)* Nitrification - reduced nitrogen (ammonia (NH3) or ammonium ion (NH4+)) oxidized to *nitrite (NO2-)* (mostly) and nitrate ions (NO3-) Both make nitrous oxide byproduct (N2O) - in anaerobic conditions, has less O than intended nitrite ion - in aerobic conditions, has more O than intended N2

6. How do you convert from mole fraction to ppm or ppb?

...

9. How can the solubility of SO2 in aqueous particles be calculated? How can the pH of these particles then be determined?

... More complicated for SO2, since its aq form is H2SO3 SO2(g) + H2O(aq) <> H2SO3(aq) Henry's law expression doesn't include H2O .... (see 117 if lecture doesn't cover it) -------------- *for pH* Need an *ICE table*, Ka, equilibrium expression for acid dissociation *1) Derive equilibrium equation* ex. HClO <> H+ + ClO- *2) Write out expression for Ka from the equation*, where Ka = sum of concentration of products / sum concentration of reactants ex. Ka = [H+][ClO-] / [HClO] *3) Write out ICE table* - ICE = initial concentrations, change in concentration, and concentration and equilibrium ex. If initial concentration was 0.35 M HClO H+ ClO- I 0.35 | 0 | 0 C -x | +x | +x E 0.35-x | +x | +x (combine I and C to get E) *4) Plug these values into Ka expression* - ex. assuming Ka = 3.5*10^-8 3.5*10^-8 = (x)(x) / (0.35 - x) - *x is small assumption* can be made if Ka is small and we have a relatively large concentration of weak acid initially (different orders of magnitude) - assumes that 0.35 >> Ka so that .35-x ~ .35 alone This turns into: 3.5*10^-8 = (x)(x) / (0.35 ) v 1.11*10^-4 = x 5) *Plug in equilibrium concentration of [H+] into pH = -log[H+]* - in this case, x = [H+] at equilibrium, so plug that in to get pH

4. What non-CFC chlorine-containing compounds are important as ozone-depleting substances?

1) *Carbon tetrachloride* (CCl4) - an *ozone depleting substance* (ODS) - Long atmospheric lifetime 2) *Methyl chloroform* (CH3-CCl3) - Concentration has declined rapidly due to shorter life - Negligible at this point 3) Halons

12. What are the three "regions" of UV light? Why is ozone more effective at shielding Earth from UV-C light than it is UV-B light? Which of the UV regions is most biologically harmful?

1) *UV-C* (200-280 nm) - better at absorbing light in these (wavelengths than in UV-B - O2 and Ozone filter out - Worst (highest energy) 2) *UV-B* (280-320 nm) - Most biologically harmful - causes sunburn + suntan + skin cancer (ex. malignant melanoma) - Can be absorbed by DNA molecules 3) *UV-A* (320-400 nm) - No part of atmosphere absorbs this - Least biologically harmful

2. What are the regions of the atmosphere? How are these regions defined? Is the altitude at which one region ends and another begins fixed or variable?

1) *troposphere* - Ground to 15 kilometers altitude - 85% of atmosphere mass 2) *stratosphere* - 15-59 km altitude - Definition: region between altitudes where temperature trends reverse - bottom = where temp stops decreasing with height and begins to increase - top = where temp stops increasing w/ height and begins decreasing 3-ish) Mesosphere - above stratosphere Above are thermosphere and exosphere Gas density and pressure decrease as altitude increases --------------- Troposphere defined by temperature reversal trends NOT altitude Altitude between troposphere and stratosphere varies - based on season + lattitude

20. What strategies are in place to further reduce smog-producing emissions?

1) Air quality agreement between US and canada - Reduce NOx + VOX - Lowering of sulfur level max in gasoline 2) Gothenburg protocol - controls release of pollutants in Europe - VOC, NOx, etc

9. Which geographic areas have seen the biggest effects of warming temperatures?

1) Air temperatures over land areas have experienced greater increase than those over seas 2) Arctic region has warmed most, causing the sea ice to disappear

17. What other factors likely contribute to mid-latitude ozone depletion?

1) Background mechanism on background concentration of sulfuric particles (carbonyl sulfide (COS) oxidation) 2) Springtime dilution of ozone depleted polar air > transport out of polar regions 3) Changes in solar cycle 4) Natural + anthropogenic changes in pattern of atmospheric transport + temps

13. What compounds have been effectively reduced using legislated Air Quality standards?

1) CO 2) NO2 3) SO2

11. What are the anthropogenic causes of increased CO2 concentrations?

1) Combustion of fossil fuels - coal, oil, natural gas - 3/4 from this 2) Forest clearance and wood burning for agriculture - ~ 1/4 of anthropogenic release of CO2 3) cement production

14. Why have catalytic converters typically been less effective on diesel engines? What change is diesel fuel makes it possible to use more effective catalytic converters?

1) Due to less active catalyst formations that have to be used with diesels because of high sulfur content - Highly active catalysts oxidize the sulfur dioxide to sulfate particles > renders catalyst ineffective 2) Also run with excess air (more NOx, less CO) Using low-sulfur fuel allows for more effective converters to be used

22. What compounds are considered to be the end-products of smog?

1) HNO3 2) O3 (81)

19. What three conditions are necessary for an episode of photochemical smog to occur?

1) Have to have enough vehicle traffic to produce enough NO, reactive hydrocarbons, and other VOCs 2) Must have warmth and ample sunlight for rxns to proceed rapidly 3) Needs little movement of air so that reactants aren't quickly diluted or swept away

27. What major cities commonly have issues with photochemical smog, and why?

1) Los angeles - large number of vehicles + increasing population 2) Mexico city - Worst in winter months, when temp inversions prevent pollutants from escaping - butenes (component of liquefied gas used for cooking/heating) 3) Athens + rome - Limit vehicles 4) France 5) Houstoun - Emissions of highly reactive VOCs containing C=C bonds from region encompassing petrochemical industry 6) Charlotte, North Carolina --------------------- - Increase of vehicles on road, warm climates (developing countries) > Beijing, shanghai, guangzhou

17. What strategies are used to minimize NO emissions from power plants? 18. What is selective catalytic reduction, and how does it work? 19. What is wet scrubbing of exhaust gases, and how does it work? (pg 99)

1) Lower temperature of flame / recirculate exhaust gases 2) Have combustion for fuel occur in stages - First high-temp stage: no excess oxygen present, limiting rxns with N2 - 2nd lower temp stage, oxygen is added to complete combustion. Low temp reduces NO produced 3) Add catalytic converters that change NOx to N2 - *selective catalytic reduction* systems - NH3 added to reduce - 4NH3 + 4NO + O2 > 4N2 + 6H2O - Need to control process to prevent oxidation of NH3 to NOx 4) *Wet scrubbing of exhaust gases* - NO insoluble in water + aqueous solutions, so *need at least half to be NO2 for this to work* - *Sodium hydroxide* (NaOH) reacts w/ NO and NO2 to produce *sodium nitrite* (NaNO2) - NO + NO2 + 2NaOH > 2NaNO2 + H2O

2. What two types of species typically drive the rate of the photochemical smog reaction?

1) Nitrogen oxides (NOx) 2) VOCs

12. What are some currently observable signs that the climate is changing?

1) Rise in average global surface air temperature 2) Precipitation has increased in most areas, but decreased in others - Northern hemisphere up (N/S america, europe, and asia) - Areas just north or south of the equator, esp AFrica and souther Asia, became much drier 3) Extreme weather is becoming more common - increase in hot weather/record hot weather days - less cold weather - *extreme events are at edge of normal temp distribution, which is greatly changed by a small shift in the distribution curve* 4) Winters have become shorter by ~ 11 days - spring arriving sooner and autumn starting later (northern hemisphere) - Range of plants has increased towards poles - Season-dependent behaviors of animals/plants have shown earlier starts 5) Earth's ice cover is shrinking fast - delayed seasonal formation of ice + melting glaciers 6) Warming water is killing a lot of coral in ocean reefs and threatening sea life 7) Mosquito-borne diseases have reached higher altitudes - can get to new regions 8) Rising seas are threatening to engulf pacific islands - accelerated rising sea levels

SO2 contribution to acid rain

1) SO2 dissolves in rainwater to yield H2SO3 (a weak acid) SO2 (g) + H2O (aq) > H2SO3 (aq) 2) H2SO3 partially dissociates to yield HSO3- and H+ H2SO3 (aq) <> HSOr- (aq) + H+ (aq) 3) HSO3- then oxidized to HSO4- - by peroxide (H2O2) - by Ozone (O3) - by oxygen (O2) in presence of certain metal ions H2SO4 is a strong acid, so H+ will not re-associate, increasing acidity of rain

9. What are the different common measurements of the extent of ozone depletion? How has the magnitude of these measurements for the Antarctic ozone hole changed over time?

1) Surface area of ozone hole (low ozone) - Increased rapidly and linearly during 1980s - Max depletion = 1998, 2006 - Neither overall increase or decrease since early 1990s 2) Min amount of overhead ozone - Decreased sharply from 1978 to late 1980s, then slowed - Min ozone has been constant since 1990s 3) Average length of time that ozone depletion occurs - Has increased (mid-winter and summer, on top of spring) - Some persistence in depletion from one year to the next 4) Vertical region - Where almost total ozone depletion occurs (12-22 km) - HAsn't increased since mid 1990s

Catalytic converter limitations

1) Temperature - must be heated enough for catalysis to occur (cold start problem) 2) Air/fuel ratio - Too much air, NOx won't reduce - Too little air (oxygen), CO/hydrocarbons (carbon containing compounds) won't oxidize ~1 ideal 3) NOx catalyst also reduces SO2 to H2S - H2S smells and is toxic - Reduction in S content of fuel necesary

1. What is the general form of the reaction by which a molecule or atom (designated as X) removes an oxygen atom from ozone? 2. What is the subsequent reaction of XO with atomic oxygen? 3. Why is X considered a catalyst of ozone destruction in this sequence of reactions?

1. X = Free radical atomic/molecular species that react w/ ozone and remove an O from it Mechansim i X + O3 > XO + O2 ---------------- 2. XO + O > X + O2 X reformed ----------------- Overall reaction O3 + O > 2O2 X are catalysts bc they lower activation E of the reaction and are reformed after (not used up)

6. What is the maximum wavelength of photon with sufficient energy to drive the dissociation of O2? Why is this a maximum (not a minimum)? How can this wavelength be calculated?

240 nm or shorter = sufficient This is a max because it's the longest wavelength that would have enough energy - longer wavelengths would have less E Can be calculated by: 1) Calculating enthalpy of O2 > 2O rxn ΔH° = ΣΔH°f (products) - ΣΔH°f (reactants) ------- 2) Plug in that enthalpy to the E of this equation λ = (hc)/E Note: hc = 119,627 kJ/mol nm

9. What reactions take place in a catalytic converter to break down incompletely oxidized carbon-containing compounds?

2CO + O2 > 2CO2 CnHm + (n + m/4) O2 > nCO2 { m/2H2O ex. CH2O + O2 > CO2 + H2O

10. What reactions take place in a catalytic converter to break down incompletely reduced nitrogen compounds?

2NO > N2 + O2 overall via 2 NO + 2H2 > N2 + 2H2O ------------ 3 way converter (lecture) catalyze reduction of NO to N2 and O2 using CO, H2, and unburned hydrocarbons as reducing agents Ex. 2 NO + 2CO > 2N2 + 2CO2

5. What reaction does chlorine nitrate (ClONO2) undergo at the surface of PSC ice crystals? 6. What reaction does *hydrogen chloride* undergo at the surface of PSC ice crystals (aqueous layer)? 7. What reaction subsequently takes place between hypochlorous acid and chloride ion? 8. What molecules released from the surface of the crystals produce atomic chlorine upon photodecomposition?

5. Gaseous *chlorine nitrate* reacts with water molecules on surface of PSC to form *hypochlorous acid* (HOCl) ClONO2 (g) + H2O (aq) > HOCl (aq) + HNO3 (aq) ------------------------------- 6. Redox rxn (...review) HCl (g) > H+ (aq) + Cl- (aq) aqueous layer ------------------------------- 7. Reaction between oxidized Cl- and reduced HOCl makes *molecular chlorine* (Cl2) Cl- (aq) + HOCl (aq) > Cl2 (g) + OH- (Aq) ------------------------------- Cl2 + sunlight > 2Cl HOCl (g) + sunlight > OH + Cl

8. What region of the electromagnetic spectrum (in nm) is ultraviolet light?

50-400 nm

6. What reaction occurs between the hydroxyl radial and carbon monoxide (where is the OH attacking? Please see lecture video for correction on pg. 74 Lewis Structures)? Is this reaction efficient? What does this mean for the lifetime of carbon monoxide in the environment? -------------- 7. How does molecular oxygen react with the radical formed by hydroxyl radical attack on carbon monoxide? What are the products of this reaction? -------------- 8. How is the hydroperoxy radical converted back to hydroxyl radical?

6. OH adds self to the molecule OH + CO > HOCO Most collisions not effective, so the lifetime of CO is 1-2 months General form OH + stable VOC + O2 light > HOO ----------------------------- 7. It reacts quickly with transient free radicals (ex. HOCO), causing the oxidation complex - Takes a H atom from free radical, forming *hydroperoxy free radical* (HOO) and the fully oxidized product CO2 O2 + HOCO > OOH + CO2 ----------------------------- 8. Converted back via oxidation of *Nitric oxide* OOH + NO > OH + NO2

1. What are the main components of the earth's atmosphere?

78% N2 (*diatomic nitrogen*) 21% O2 (*diatomic oxygen*) 1% Ar (Argon) 0.04% Co2 (*Carbon dioxide*) Water vapor 0-4% Trace gases in trace amounts (very important)

3. How can the enthalpy of a reaction be calculated from the enthalpies of formation of the products and reactants in that reaction?

= Know - ΔH° = sum of enthalpies of formation (ΔH°f) of the products - the reactants ΔH° = ΣΔH°f (products) - ΣΔH°f (reactants) reactants must be multiplied by stoichiometric coefficients enthalpy of formation for species in standard state = 0 ---------- To find energy for a single photon, must convert kJ/mol to J/photon

2. What is an ecological footprint?

A measurement of how much space is needed to sustain resource use (or a certain lifestyle) v Became a standardized system of tracking biocapacity usage + availability - How much stuff was used, and how much was available Based on 1) Biologically productive land 2) Ocean space 3) Land required for waste More countries are exceeding the biocapacity

4. What is the difference between absolute concentration of a gas and relative concentration of a gas?

Absolute concentration - number of molecules per cubic centimeter of air OR partial pressure (in units of atmospheres, kiloPascals, or bars) - molarity used in absolute concentration - mass (?) *ideal gas law* (PV = nRT) ---------------- Relative concentration - based on *mole fraction* scale - parts per ______ values (ppm, ppb, ppmv, etc) > v emphasizes that it's a volume - number of *molecules* of a pollutant (aka. solute) in million, etc. *molecules* of air > represent *volume* a pollutant would occupy vs. a set volume of air (if pollutant was compressed until the two pressures were equal)

16. Where does water vapor absorb in the IR spectrum? How does water vapor rank with regard to how much greenhouse warming it is responsible for?

Absorb IR light through HOH *bending vibration as well as symmetric + asymmetric stretching* > however stretching absorptions are outside of thermal IR - *peak absorption around 6.3 um* > absorbs almost all IR around *5.5-7.5 um* - Absorption that increases rotational energy absorbs thermal IR of 18 um and longer Most important greenhouse gas in the Earth's atmosphere - *more greenhouse warming than any other gas* - per molecule it is less efficient at absorption than CO2 > present in higher amounts

15. What photochemical reaction accounts for much of the ozone destruction in the middle and upper stratosphere?

Absorption of UV-C or UV-B by ozone molecules O3 + UV photon ( <320 nm) > O2* + O*

13. Why are fine particles in many areas acidic? What process occurs to neutralize the acidity in these particles? Why are course particles mainly basic?

Acidic because they have sulfuric and nitric acids They are neutralized via an acid-base reaction with ammonia (from biological decay) and transformed into soluble salts: *ammonium sulfate* ((NH4)2SO4) and *ammonium nitrate* (NH4NO3) - bc sulfuric acid has 2 H ions, neutralization occurs in two stages. *ammonium bisulfate* is made as an intermediate Ammonia starts as urea (CO(NH2)2) and hydrolyzes to ammonia CO(NH2)2 + H2O > 2 NH3 + CO2 then reacts as described above: H2SO4(aq) + NH3(g) > NH4HSO4(aq) NH4HSO4(aq) + NH3(g) > (NH4)2SO4(aq) Ammonium ion can become acidic (see 123 for more ions in fine particles) HNO3 follows a similar process (reacting w/ NH3 to make NH4NO3), but doesn't require a second step ---------------------- Coarse are basic due to their soil content

12. What are the steps in Mechanism II? Why is atomic oxygen not necessary in Mechanism II? What is the overall reaction in Mechanism II?

Acts in lower stratosphere (where concentration x is high, but O is low) - depletion by man-made chemicals (primarily responsible for ozone hole) Steps: Initial: X + O3 > XO + O2 X' + O3 > X'O + O2 - X' = doesn't have to be same atom - One X must be chlorine, other can be chlorine or bromine - Doesn't happen if either is NO!! (only a catalyst in mechanism I) Regeneration: XO + X'O > [XOOX'] > X + X' + O2 ---------------- No atomic O involved because it was never involved ---------------- Overall 2O3 > 3O2 Mnemonic: Use 2 catalysts to make mechanism 2 happen

7. What are the advantages and disadvantages to using these molecules (HCFCs) as CFC replacements?

Adv 1) Removed from air before they can reach stratosphere - less long term threat Disadv 1) Decomposes to release Cl- more quickly (greater short term ozone destruction)

1. What is an aerosol? What are the two major sources of aerosols in the atmosphere?

Aerosol is a collection of particulates, solid or liquid, dispersed in air - contains very small particles (diameters less than 100 um) -------------- 1) Volcanic eruptions 2) Production via industrial processes

8. At what altitudes in the stratosphere does the ozone depletion take place? Why does the depletion happen in the specific time periods that it does?

Altitudes - upper stratosphere (pg 40)... Recovery started happening in the 1997-2008 decade because the cholrine concentration started to decline (compared to previous 2 decades)

18. What have the effects of ozone depletion been on the amount of UV light at ground level?

Amount of UV-B reaching ground level increases by 3-6 times in Antarctic

6. What is necessary regarding energy absorption and emission for the planet to stay at the same temperature?

Amount of energy absorbed (from sun) must be equal to amount that it emits (loss from earth) to stay level (be @ equilibrium)

What anthropogenic activities lead to release of N2O? What are the natural sources? What is the atmospheric fate of N2O?

Anthropogenic 1) Synthesis of adipic acid using nitric acid (HNO3) to eventually make nylon 2) Increased use of fertilizers (both synth and organic) for agriculture (majority) - have ammonium salts which, when oxidized, become N2O 3) Aerobic decomposition of livestock manure (anaerobic doesn't make much) - changing animal diets can alter amount 4) Fuel combustion - catalytic converters (reduce NO to diatomic conditions, but if excess oxygen, can get N2O) Natural 1) Release by oceans 2) Processes in the soils (especially tropical regions) --------------- Atmospheric fate - *no sinks for nitrous oxide (N2O) in troposphere* - all eventually rises to stratosphere, where it absorbs UV light and decomposes to N2 + O, or reacts with O Lifetime ~ 120 years

7. How does atom economy relate to percent yield?

Application of green chemistry (principle 2) *Percent yield* = measure of actual yield of a desired product relative to the amount predicted based on a balanced chemical equation - How well a given synthesis works at given conditions - (Actual yield/theoretical yield) *100% Want a higher percent yield to be more efficient, but they aren't the same...

6. How can the X catalysts be classified chemically?

As *free radicals* - atoms/molecules containing odd #'s of electrons, making them very reactive - depicted as . (different from asterisks!)

15. What is an atmospheric brown cloud, and what are the consequences of these clouds?

Atmospheric brown cloud - Originates mainly from forest fires (secondary from underground fires that burn in coal and peat deposits) - A cloud of particles + gases from forest fires, vehicle exhaust, and domestic cookers that burn wood, dung, and agricultural waste (especially in rural areas) - Covers most of east + southeast asia from december to may (main season for home heating - significant "black carbon" content (unlike pollution aerosol over NA and europe) Consequences 1) Lowers light levels at surface, reducing crop yield 2) Alters rainfall + monsoon patterns ...

20. What is the atmospheric window, and what wavelengths are included in the atmospheric window? What is the concern with trace gases in the atmosphere that absorb wavelengths in the atmospheric window?

Atmospheric window: - The portion of the electromagnetic spectrum that escapes the atmosphere efficiently (~ 8-13 um) Concern: - If trace gases are added that absorb the atmospheric window, the greenhouse effect will be increased > other greenhouse gases are already absorbing regions outside the window (a lot), so trace gases aren't absorbing much of that - *fraction of light absorbed by a gas is logarithmic related to concentration C* via beer-lambert law > logarithmic functions are almost linear near C = 0, so warming by trace gases is linearly proportional Gases that absorb within the atmospheric window are problematic even in small amounts

10. What is the prevalent form of oxygen in the regions above the stratosphere? Why?

Atomic oxygen (O) - Concentration of O is low Even when they do collide and make O2, they soon dissociate again due to UV-C exposure

14. What is the primary cause of negative biological effects from sunlight?

Because UV-B can be absorbed by DNA (especially <300 nm), which may mutate causing cancers, etc

9. Why is chlorine returned to a catalytically inactive form shortly after PSCs disappear?

Because air with normal amounts of NO2 mixes with polar air that was trapped in the vortex, forming chlorine nitrate (CLONO2) + HCL again Cl2 not actively formed now NO2 freed from crystals HNO3 + UV > NO2 + OH - Air mixes - can react w/ chlorine

3. Why is the stratosphere usually cloudless? What is different about the stratosphere over the South Pole in winter months?

Because concentration of water (which would condense into clouds) is very small Lower stratosphere drops to low temps (-80 degrees C), allowing condensation to occur

10. How does the melting of sea ice produce a positive feedback?

Because ice reflects sunlight more efficiently than liquid water - more sunlight absorbed as water replaces ice raises surface water/surface air temperatures

8. When light energy drives a reaction, why does the energy to drive that reaction typically have to come from a single photon?

Because molecules can't store energy from multiple photons until they have enough E to react (will lose it through photon release or heat)

11. Why is the cooling effect of aerosols short-term relative to the warming effect of gases like CO2?

Because of different atmospheric lifetimes of the particles as compared to the gases - lasts only a few days and don't accumulate with time CO2 emissions are cumulative (exert effects over decades or centuries) Cumulation true for CFCs and N2O (nitrous oxide), but less for methane bc its half life is only a decade Eventually cumulative effects win out

2. Why must these take place on the surface of particles instead of in the gas phase? What chemicals comprise the particles where this conversion takes place?

Because the gas phase is too slow. Conversion of inactive to active chlorine occurs quickly only when on surface of cold particles Water, *sulfuric acid* (H2SO4), *nitric acid* (HNO3 (formed by *hydroxyl radical* OH with NO2 (*nitrogen dioxide*))

19. Why is almost all of the bromine in the stratosphere in catalytically active form? Why is bromine then not as important to ozone destruction as chlorine is?

Because the inactive forms (*Hydrogen bromide* (HBr) and *bromine nitrate* (BRONO2)) are broken down easily by sunlight - Also has slower transformation into HBr due to high activation energy (endothermic) --------------- Because, even though it more efficiently destroys O3, there is less of it than Cl

2. Why do concentration measures for particles in the air use particle mass rather than numbers of atoms or molecules in the numerator?

Because the particles are heterogenous mixtures, and can't have molar mass applied with them.

7. Why do exothermic free-radical reactions have fast reaction rates? (Refer the Box 1-1, and be sure to address the activation energy and endo/exothermicity of the reaction.)

Because they have low activation energies - Form new bonds Endothermic rxns need energy, so they have very high activation Es

19. Why are the warming effects of increased water vapor generally attributed to the action of other greenhouse gases?

Because water's effects are due to the indirect effect of increasing other greenhouse gases Can't directly control it Water droplets in cloud can absorb IR radiation AND reflect incoming light - so overall effect of clouds is currently being studied

4. Why is the above mechanism of ozone destruction (Mechanism I) of particular environmental concern? Humans have released gases into the atmosphere that contain which elements that can act as X in the above reaction?

Because we've increased X (especially Bromine and chlorine) - very efficient x catalysts Results in ozone depletion

4. What is a bending vibration? Which molecules will have this type of vibration?

Bending vibration - oscillation between two atoms X and Z bonded to a common atom Y (but not to each other) > increase, decrease, increase, etc - alters XYZ bond *angle from average value (Φ)* Done by all molecules with 3+ atoms Frequency of this is often in thermal IR region

3. What is a bond-stretching vibration? What affects the frequency of oscillations in this motion?

Bond-stretching vibration - oscillatory motion of two bonded atoms X and Y relative to each other - Increases beyond its average value R, returns to R, then contracts to lesser value, and finally returns to R (closer then further apart - like rubber band stretched straight across) - *average bond length changes* Frequency of oscillations affected by: 1) type of bond - single, double triple 2) type of atoms involved

17. Why do the concentrations of OH and HOO build up during an episode of photochemical smog? What does this do to the smog reaction?

Builds up because more than 1 of each are created per cycle This accelerates the cycle overall

23. How can the rate law for production of NO from N2 and O2 be determined (you may need to review your gen-chem kinetics!)? Why does this reaction proceed slowly in conditions of low O2 concentration?

By looking at elementary reactions... O2 <> 2O O + N2 > NO + N (rate limiting) ------------ Slow bc [O] is proportional to sq root of O2 Rate of NO formation = [N2][O2]^.5 ... (83)

16. How does hydroxyl radical initiate a reaction with a compound that does not have a double bond?

By taking a hydrogen atom from it, forming water an leaving a free radical fragment of the hydride Ex. CH4 + OH > CH3 + H2O CH3 has an odd # electrons (methyl free radical) Only happens when OH concentration is high, bc is slower than rxn with multiple bonds

11. Why do sulfur levels need to be limited in fuel for engines with catalytic converters?

CAtalyst that reduces NO to nitrogen also reduces *sulfur dioxide* (SO2) to *hydrogen sulfide* (H2S) - Sulfur molecules can partly deactivate catalytic converters

2. What are CFCs, and why were they widely used? Why do they eventually end up in the stratosphere?

CFC = *chlorofluorocarbon* - Compounds containing only C, F, and Cl atoms - Main source of Cl atoms in stratosphere Used bc they were nontoxic, nonflammable, nonreactive, and has useful condensation properties - Safer refrigerants Have no tropospheric sink, so all the molecules eventually reach the stratosphere

1. What types of vibrations in methane lead to IR absorption?

CH4 (methane) is next most important greenhouse gas (after H2O & CO2) H-C-H bond-angle-bending vibrations absorb at 7.7 um (near edge of thermal IR window) - absorbs IR in this region Antisymmetric stretching is outside of thermal IR

14. What is CO2 fertilization? What effect does this have on CO2 concentrations?

CO2 fertilization - increase in growth rate of some types of trees due to increased CO2 concentration in air Effect - Causes annual atmospheric CO2 loss (184)

22. Why can liquid carbon dioxide be used as a solvent to replace VOCs? How has this been put to use in a practical setting?

Can be used because: 1) Has low vicosity + polarity, and its wetting ability - Low polarity allows it to dissolve many small organic molecules, but not larger ones (ex. polymers, waxes) > Surfactants allow it to dissolve wider range of materials (form micelles) ------------------ Practically used: 1) Dry cleaning - CO (l) drained after wash cycle, and evaporates after pressure is reduced - Can be recaptured, liquified, and used again

12. Why do engines produce most emissions immediately after start-up? How are catalytic converters being redesigned to avoid this problem?

Catalysts are cold, so converters cannot operate effectively. Also fuel-rich mixtures are fed in. Combined with high acceleration, incompletely oxidized CO and hydrocarbons are emitted directly into air under oxygen starved conditions Redesigns: 1) Converter that will operated at lower temps/can be preheated 2) Storing pollutants until engine + converter are heated 3) Recirculating engine exhaust through engine until rxns are more complete

3. What chemical reactions result when smog reactions are *NOX limited*?

Changing amount of VOC has little effect on [O3] Peroxy free radicals (HOO & ROO) from abundance of VOC oxidize NO to NO2: HOO + NO > OH + NO2 NO2 + Sun produces oxygen atoms that react w/ O2 to produce ozone

5. What is the general cause of the Antarctic ozone hole?

Chlorine pollution Temperature + sunlight (destruction doesn't start till spring) - specific weather conditions

12. What are common sources of coarse particles? What are common sources of fine particles?

Coarse - most coarse particles are primary (pollutant distinction) 1) Wind storms 2) Wind - makes coarse particles by mechanical disintegration of leaf litter 3) Pollen 4) Wildfires + volcanic eruptions (both fine and coarse) 5) Near and above oceans - NaCl high (from ocean waves) ------------------ Fine - Made by chemical reactions between gases and coagulation of smaller species - Important fine particles consist mostly fo inorganic compounds of sulfur and nitrogen 1) Wearing of tires and vehicle brakes 2) Dust from metal smelting 3) Incomplete combustion of carbon-based fuels (coal, oil, gasoline)

4. What are common naturally occurring trace gases in the atmosphere? Why does the concentration of these gases not build up?

Common trace gases 1) *Carbon monoxide* (CO) 2) *Nitric oxide* (NO) 3) *Sulfur dioxie* (SO2) 4) *ammonia* (NH4) 5) *hydrogen sulfide* (H2S) 6) *methane* (CH4) They don't build up because they have sinks, which results in destruction - oxidation rxns

6. What type of molecule is being implemented as a direct replacement for CFCs? What reaction can these molecules undergo that CFCs can't that gives them a tropospheric sink?

Compounds that contain hydrogen atoms bonded w/ carbon (*hydrochlorofluorocarbons (HCFCs)*) Reactions - hydrogen abstraction - OH attack OH + HCX3 > H2O + CX3 >> CO2 and other products

6. In what regions of the globe are the effects of sulfate aerosol seen? Why? What is responsible for the lifetime limitations of these droplets?

Concentrated in Northern hemisphere - because most industrial activity takes place there = most emissions Short lifetime stops their spreading to the southern hemisphere - they are efficiently removed by rain, so their lifespan is days rather than years

8. What have historical trends in atmospheric N2O concentrations been?

Constant atmospheric concentration until ~ 300 years ago Then began to increase from 275 ppb (preindustrial) by just 17% to 323 ppb (2010) erratic ~ 1990s, but linear growth after

1. What chemical conversions result in the catalytic depletion of ozone that leads to the ozone hole?

Conversion of inactivated chlorine to activated chlorine - converts all chlorine to active form temporarily, leading to annual depletion of ozone

3. How can H2S from natural gas and oil be converted to elemental sulfur? Why is removal of H2S important?

Converted using the *Claus reaction* 1st step (thermal) results in oxidation of H2S to SO2 2H2S + 3O2 > 2SO2 + 2H2O v 2nd step is to react H2S and SO2 then react to yield elemental sulfur (both thermal and catalyzed) 2H2S + SO2 < 3S + 2H2O - REDOX reaction of reduced (H2S) and oxidized (SO2) analagous 1/3 molar amount of hydrogen sulfide (H2S) from fossil fuel is combusted to SO2 --------------- Can be burned off in "flaring" - 60% effective Elemental sulfur is environmentally benign Important to remove HS2 from gases before their dispersal bc it is highly poisonous (more than sulfur dioxide)

16. What reaction leads to the formation of atomic chlorine from methyl chloride? How does this then go on to destroy ozone via Mechanism I?

Decomposition: CH3Cl > CL + CH3 UV-C or OH + CH3Cl > Cl + other products --------------- Destruction of ozone: Cl + O3 > ClO + O2 ClO + O > Cl + O2 Overall: O3 + O > 2O2

16. How does the thinning of the atmosphere with height affect how IR is absorbed and reemitted at higher and higher altitudes? From which layer of the atmosphere does emitted IR reach space without being reabsorbed?

Decreases the amount of IR absorbed, because less particles are available to absorb/re-emit it. IR emitted into upper troposphere doesn't get absorbed

How can volcanic eruptions illustrate both direct and indirect effects of these particles on climate?

Direct - Absorbed incoming sunlight in short term, warming the area Indirect - stratospheric aerosol that remained suspended for months (formed by SO2 that had been blasted into the air) - Decreased air temperature, globally

5. What are the direct and indirect effects of sulfate aerosols?

Direct - direct = reflection by particles themselves - cools air near ground level and thereby offset some of the global warming induced by GH gases Indirect - indirect = effects that happen when sulfate particles act as nuclei for formation of small water droplets - more effective in backscattering light than those of equal/greater mass - small drops are less likely to gather into rainclouds, so last longer and reflect for longer periods ------------------ Both result in more sunlight being reflected back to space, cooling the surface

9. In what direct ways can CFCs contribute to global warming? In what indirect ways can these molecules affect global warming?

Direct 1) High efficiency + absorbing in atmospheric window (8-13 um) = potential to cause same amount of global warming gas tens of thousands of CO2 molecules (but has small net effect) - strong per-molecule absorbance 2) Warming cancelled? by CFC cooling effect (but occur at different levels so may affect weather) - depletes ozone, allowing more UV to reach earth ------------------ Indirect 1) Use of CFC in insulating freezers, refrigerators, and air conditioners has reduced the energy needs, thus reducing CO2 emissions from electricity production no tropospheric sink, so long lifetime in troposphere *significant greenhouse gases*

4. What is a dissociation reaction? What are the products of the dissociation reaction of molecular oxygen (O2)?

Dissociation reaction = when atoms dissociate from molecules in rxn (ex. O2 > 2O) "photochemically dissociated/decomposed or photolysis" when driven by a photon

1. What makes Earth's atmosphere an oxidizing environment? Why is this important?

Due to large concentration of O2 Important because it allows for air to be cleansed. Pollutants are oxidized and end up back on the ground

11. Why can fine particles remain suspended in air for long periods of time? What is a common way for particles to be naturally removed from tropospheric air?

Due to turbulence - According to Stoke's law, rate (distance per second) at which particles settle increases w/ square of their diameter - a particle half size will fall 4x more slowly Small particles fall so slowly that they're basically suspended ---------------- Removed: 1) Particles aggregate to form larger ones - stay for days or weeks 2) *particles removed from troposphere by incorporation into falling raindrops* - usually within a week or 2

1. How is the energy of a photon related to the frequency and wavelength?

E = hv λv = c E = (hc)/λ --------------- E = energy fo photon v = frequency λ = wavelength in meters (if using h and c indivdiually) h = Planck's constant (6.626 x 10^-34 J s) c = speed of light (2.998 x 10^8 m/s) hc = 119,627 kJ/mol nm -------------------- energy proportional to wavlength Shorter wavelengths of light have higher energy Higher frequency = higher energy

21. What reactions take place in the early morning hours of an episode of photochemical smog? How do the concentrations of primary and secondary pollutants change during the course of a day, and why?

Early morning: - [NO] and [VOC] increase due to morning traffic - [OH] forms as sun comes out > [OOH] converts NO to NO2 - [O3] doesn't increase, bc it is destroyed by excess NO O3 + NO > O2 + NO2 (80) Midmorning - [VOCs] oxidized by OH (aldehydes - oxidation intermediate) - [OH] free radicals increased > hydrocarbons decline - Less [NO] in air (less traffic + being converted to NO2) - [NO2] increases and peaks, is converted to HNO3 by OH, but formed by continued emissions of NO - [O3] builds rapidly (less NO = no longer destroyed) Later - [O3] peaks around 12 or 2 - [Aldehydes] decrease (production < photochemical/free radical decomposition) - sink exists for NO2 (NO2 + OH > HNO3)

4. What is an "end-of-the-pipe solution" to an environmental problem? Why is a preventative solution preferable to an end-of-the-pipe solution?

End-of-the-pipe: - Focuses on preventing effects of waste that is created (dispersion, exposure, etc) Preventative: - Focuses on minimizing waste produced - Better because: a) the end of pipe solution can fail, resulting in waste exposure > Not a failsafe b) Don't have to control exposure, dispersion, or clean up hazardous waste, bc it wouldn't happen!

1. What is the primary source of energy that warms the Earth and its atmosphere?

Energy from the sun

7. What is an excited state? How is this denoted on a molecule/atom (at least in our book—some use different notations)? What are the possible outcomes when an excited molecule/atom returns to the ground state?

Excited state = state in which electron organization is changed to high energy state - Don't stay in this state/retain the energy for long Denoted with an * Outcomes: 1) React photochemically 2) Return to *ground state* = lowest energy/ most stable electron arrangement - do this by A) release photon B) converting E to heat - use it or lose it

17. What factors determine the amount of water vapor present in the troposphere? How do the concentrations of other greenhouse gases affect water vapor concentrations?

Factors: = Determined primarily by temperature and other weather aspects - some anthropogenic influence (ex. burning of fossil fuels) - almost all H2O in troposphere comes from evaporation fo liquid and solid water on Earth's surface and in clouds > influenced by temperature Concentrations: - Other greenhouse gases increase air temperature, which increases the rate of evaporation

8. How can the concentration of a dissolved gas be calculated using its Henry's Law constant?

For H2O2 *1) Consider equilibrium between the gas and liquid forms* H2O2 (g) <> H2O2 (aq) *2) Use Henry law's constant (Kh) to solve for M* Kh = concentration of dissolved species (aq Molarity) divided by partial pressure of gas (in atm) Kh = [aq] / P(g) Assuming concentration is in molarity and pressure units are atmospheres (M/atm), can rearrange the equation to solve for molarity (solubility) of aq substance in a raindrop

18. Why are NO and VOCs said to act synergistically in the smog reaction?

For the cycle to run, they both have to be there simultaneously (otherwise rxn would go much slower) Synergism => overall effect much greater than would be the sum of either acting in isolation

4. How are scrubber processes used to remove dilute SO2 from exhaust gases? How can the resulting products be converted to a commercially desirable substance?

Formally known as *flue-gas desulfurization* Acid-base rxn between SO2 (g), *calcium carbonate* (limestone), CaCO3, or *calcium oxide* (CaO) as wet crushed solids - gases are then passed through slurry of this wet solid, or have the slurry sprayed at them Alternatively, dry scrubbing can occur - fine spray of aqueous calcium oxide or calcium carbonate used to trap sulfur dioxide - water component evaporates upon contact with the hot gases (hence dry scrubbing --------------------- Product can be fully oxidized by reaction with air, and the resulting *calcium sulfate* (CaSO4) is dewatered and sold as gypsum - commercially viable Usually, product is a mixture of *calcium sulfite* (CaSO3) and calcium sulfate (CaSO4) - partially dewatered or made into a dry solid if granular calcium oxide was used - then buried (waste) (rxn on pg 112)

10. What are the sources of hydroxyl free radical? Write out the steps by which this radical can destroy ozone.

From rxn of O* (excited) with water or methane, CH4 O* + CH4 > OH + CH3 - not as catalyst Mechanism I OH + O3 > HO2 + O2 HO2 + O > OH + O2

3. You need to be able to convert gas concentrations among units of ug/m3, mol/L, molecules/cm3, ppm, and ppb. What are some important conversion reminders or general strategies? (pg 73) - REVIEW separately

General: - independently convert units of numerator a to units of numerator p (which only involve pollutant), then convert denominator b to new value q (which cover total air sample) - a/b > p/q ug/m^3 mol/L molecules/cm^3 ppm ppb

5. What are the trends in global average surface temperatures over the past 2000 years? What changed in these trends in the last few decades?

Generally there have been periods of warming and cooling (peaks and dips), but it has remained largely flat in terms of overall change. In the last few decades (~1970 to present), there has been a warming period - attributed to anthropogenic influences alone

Ozone in stratosphere vs. troposphere + other components of smog

Good in stratosphere - Absorbs harmful UV light Troposphere bad - Strong oxidizing agent, attacks molecules w/ c=c bonds - Respiratory irritant > premature deaths ------------- Other smog parts - bad - HNO3 (nitric acid) > acid rain - PArtially oxidized organic compounds, nitrated organic compounds > toxic

14. Skim sections 5.26-5.29, read section 5.30 (you do not need to read the residence time analysis after 5.30) and review table 5-1. Choose one geoengineering method to read about in more detail (closely reading its section in the book is fine). What is the theory behind that geoengineering method? What are the advantages and drawbacks to such a plan? (213)

Ground level systems: cloud whitening - BAsed on the idea of reflecting sunlight before it is absorbed - Increase the albedo of low-level marine clouds (smaller droplets better than longer ones) > surface area of small droplets is increased, presenting more area to reflect sunlight Kept small by having them form on suspended, solid particles (cloud-condensation nuclei (ex. sea salt)) - ships would spray the cloud condensation nuclei, and be suspended through turbulence Advantages: - Particles could be cheaply produced (medium affordability) - medium timeline Drawbacks: - short lifetime of aerosol particles at low altitudes = requires constant replenishment - could affect weather patterns in deleterious ways - Low to medium (effectiveness) - Medium (effectiveness)

12. What is Harpin Technology, and why does it have potential in reducing the use of ozone depleting substances? How is Harpin consistent with the principles of green chemistry?

Hairpin - Naturally occurring bacterial protein that was isolated from the bacteria Erwinia Amylovora - Elicits natural defenses of plants - Creates nontoxic products - Biodegradable - Doesn't deplete nonrenewable resource - Short synthesis process, compared to traditional processes - More effective in that it stimulates plant growth too ... add principle numbers

9. What are halons, and what are they used for? Why are halons of concern with regards to ozone depletion?

Halon - Br/C/F and Cl containing hydrogen-free substances > No H = no tropospheric sink They have no tropospheric sinks, and rise to stratosphere - Get photochemically decomposed, releasing atomic bromine (and maybe Cl) > Mechanism II catalyst

15. What health effects are associated with exposure to UV light in humans? In other organisms?

Health effects 1) Cataracts (damage to lens) 2) Macular egeneration (gradual death of cells in center of retina) 3) Suppressed immune system 4) Vitamin D synthesis (also serves as anticancer, helps with bone growth) 5) skin cancer Organisms 1) Interference in photosynthesis > less leaves, seeds, and fruits 2) Surface water dwellers affected > affect food chain 3) Insect survival based off of plants impaired

3. In which season are concentrations of ozone normally highest? Lowest?

Highest = early spring Lowest = fall - depleted by october over anarctica - Fills back in ~ a month after

3. In which region of the atmosphere is the concentration of ozone the highest? Is the concentration of ozone globally uniform throughout this region?

Highest in the stratosphere Concentration of ozone not uniform - Highest around lower 20s (km) - lowest around late 40s (km)

6. What regions have historically had the highest level of anthropogenic SO2 emissions? What regions currently have the highest level of anthropogenic SO2 emissions?

Historically - Europe Currently - East Asia

20. In an episode of photochemical smog, what compounds are initially present? What is primarily released from vehicle emissions?

Hydrocarbons, VOCs, NOt .... NO (not NO2) is released from vehicles

How is use of ionic liquids being investigated to make use of cellulose as a replacement for some petroleum-based materials?

ILs have been found to expedite dissolution of cellulose when microwaved - Dispersing additives in IL before or after dissolution allows cellulose-based materials to be formed when polymer is regenerated Can also suspend many other materials in cellulose, making useful blends Using ILs reduces use of nonrenewable use of petroleum

7. What is the fate of most SO2 in the atmosphere? What oxidizing agents in airborne droplets are most important in this process?

In the atmosphere, most SO2 is converted to sulfuric acid after it's dissolved in suspended water droplets (cloud, mists, etc) *hydrogen peroxide* (H2O2) and ozone gases are the most important oxidizing agents - O2 oxidation is very slow unless a catalyst transition metal ion is present

NO (Nitric oxide)

Involved in initial rxns of smog Formation: N2 + O2 > 2NO Highly endothermic rxn. Only occurs at high temps If high temp maintained, will revert to N2 and O2 again - This reverse rxn has high activation energy - Some NO removed from combustion chamber before it proceeds (cars) Reaction rate is slow in conditions of low O2

23. What are ionic liquids, and why are they being investigated as alternatives to VOCs?

Ionic liquids (ILs) - Ionic compounds have high melting points due to strong ionic bonding. Some have lower melting points (<= 100 C), and these are known as ionic liquids at room temp - Usually made of bulky ions that have dispersed (rather than localized) charges + large nonpolar groups > bc of this, their ions have weak attractive interactions = low MP Of interest because: 1) Low vapor pressure - High vapor pressure solvents > VOCs 2) Nonvolatile 3) Can be purified and recycled 4) Nonflammable 5) Stable up to 300 degrees C 6) Microwavable - Heats contents directly (pg 107) - Substance must be polar/ionic, which ILs match

10. Why is fluorine in the stratosphere not a major cause of concern with regards to ozone depletion?

It cannot easily be regenerated as a catylyst, because OH bonds are weaker than HF bonds (endothermic reaction) - So it destroys some, but is quickly rendered inactive in HF

18. What temperature effect does increasing atmospheric CO2 have in the stratosphere? Why is this?

It cools the stratosphere Because: 1) More outgoing thermal IR is absorbed at low altitudes (in troposphere), so less is left to be warm/be absorbed by gases in stratosphere 2) @ stratospheric temps, CO2 emits more thermal IR upward and downward than it absorbs as photons (most absorption at that altitude is due to water vapor + ozone)

11. Why is atomic oxygen necessary for X to act as a catalyst in Mechanism I?

It is needed to regenerate X as a catalyst so that it can react again

10. What happens to IR photons that are absorbed by atmospheric gases? What is the result of this process?

It may be re-emitted, or that energy may be distributed as heat among colliding molecules (and emitted by them instead) - collision warms surrounding air Direction of emission is random, but the result is that some IR is redirected towards earth and is reabsorbed there or by the air above it (see 171 for additional info) - can eventually escape after several reabsorption and emission cycles

15. What effect is warming having on peat deposits in northern latitudes? What effect does this have on atmospheric CO2 concentrations?

It's increasing the rate of peat CO2 decomposition - increasing release of CO2 stored in peat (which has been increasing due to CO2 fertilization)

11. What is photochemical smog? What are the important initial reactants in an episode of photochemical smog?

Known as "an ozone layer in the wrong place" - Higher levels of ground-level ozone produced from light-induced chemical reactions of pollutants - Consists of mix of *ozone*, organic molecules, and nitric acid - Often in big cities with geographical air restrictions (ex. mountains) - Yellow-ish brown tint due to NO2, which absorbs purple (appearing yellow/brown) Initial reactants - VOCs (volatile organic compounds) - Nitric oxide (NO) > from vehicle traffic + power plant - Unburned hydrocarbons - Partially oxidized hydrocarbons

4. What chemical reactions result when smog reactions are *VOC limited*? How can dropping the NOX concentrations under VOC-limited conditions result in an increase in ozone production?

Large excess of NOx (low [VOC] limits ozone produced) - changing NOx (excess) has little effect on [O3] OH reacts w/ NO2 = less available to initiate rxn of more VOCs: OH + NO2 > HNO3 - OH trapped Lowering NOx produces *more* ozone bc more OH is available to react w/ VOCs - More OH freed to oxidize volatile organics - Not as quickly as increasing VOCs though

4. On a molecule-for-molecule basis, how does the warming effect of methane compare to CO2? Why?

Larger warming effect than CO2 per molecule - a significant GH gas!! CH4 molecules more likely to absorb thermal IR photons than CO2 REstricted to shorter timeframe (~1-2 decades after release) bc they're oxidized --------------------- *Warming of 1kg CH4 = 23 kg CO2 over 100 years* - much more potent!!

4. When was the Antarctic ozone hole discovered? During what time of year does the Antarctic ozone "hole" appear?

Late 1970s Appears in Spring (sep to nov)

21. Why do latex paints present a problem with emission of VOCs? How has this been addressed using chemistry?

Latex paints have an additive "coalescent", which soften/plasticizes particles of organic polymer suspended in water - When water evaporates, these particles form a thin, uniform film that stays on the material being painted - Coalescent is then emitted slowly into atmosphere, contributing to VOCs This was addressed by developing coalescents that bind via covalent bonds to self and resin, preventing their emission - It can undergo auto-oxidative cross-linking in presence of oxygen due to carbon-carbon double bonds > These have low vapor pressure and are absorbed into and bonded to resin, further reducing volatility + ability to be emitted

4. Why don't pure sulfate aerosols absorb light? How do they interact with light? What effect does this have on Earth's albedo?

Made primarily in burning of fossil fuels (esp. coal) Do not absorb sunlight bc none of their components absorb light in visible or UV-A regions (water, sulfuric acid, ammonium salts) ----------------- Anthro sulfate-rich aerosols Reflect light into spacemore than they absorb it, so they increase Earth's average albedo

13. Do the major component gases of Earth's atmosphere absorb IR light? What gases have been responsible for greenhouse warming in the past? How does this explain why cloudy nights are frequently warmer than non-cloudy ones?

Major gases (N2, O2, and Ar) can't absorb IR light Greenhouse warming gases = water vapor (2/3 of effect) and CO2 (1/4 of effect) - minor atmospheric components Because clouds are made of water vapor, they help to retain IR light (making cloudy nights warmer) - re-radiate it back to surface

25. How does NO2 contribute to the appearance of smog?

Makes it look yellowy, because NO2 absorbs purple gases

26. What governmental goals have been put in place to try to reduce photochemical smog?

Maximum allowable ozone concentrations in air averaged over a period of 8 hours - 75 ppb in US - 65 ppb Canada - European unit similar to US

10. How can past CO2 concentrations be estimated/measured? What causes seasonal fluctuations in CO2 concentrations?

Measured from air trapped in ice-core samples from Antarctica Seasonal fluctuations due to *growth spurt of plants in spring/summer* (removing CO2 from air) and *plant decay in fall/winter* (releasing CO2 into air) - photosynthesis traps CO2 in polymeric CH2O + O2 - polymeric = plant fiber - carbon trapped like this is called *fixed carbon* THese seasons in relation to north hemisphere seasons, bc that's where most of the plants are

1. What does a Dobson Unit measure, and what is it equivalent to? How many DU are typically overhead in temperate regions?

Measures the total amount of atmospheric ozone above a given point on earth 1 is equivalent to a 0.01-mm (0.001-cm) thickness of pure ozone @ the density it would have if brought to ground-level (1 atm) pressure and 0C temperature ------------- Typically there are 350 DU (=3.5 mm)

13. Which of the two catalytic ozone destruction mechanisms is dominant for depletion due to man-made chemicals?

Mechanism II

16. What is the primary mechanism of catalytic ozone destruction in the lower stratosphere in the middle latitudes?

Mechanism II - X = CL or Br - X' = OH X Cl + O > ClO + O2 X' OH + O > HO2 + O2 ClO + HOO > HOCl + O2 HOCl > OH + Cl sunlight

11. What mechanism and catalyst are responsible for most of the ozone destruction in the ozone hole? What evidence supports this?

Mechanism II with Cl as a catalyst Evidence 1) Ozone hole in lower stratosphere: not a lot of atomic O available = Mechanism I not efficient 2) Graphs plotting ClO and O3 as a funct. of latitude. Display opposite trends (as ClO increases, O3 decreases) 3) In areas where ClO is low (Away from north pole), [ozone] is higher > The edge of this concentration change (high ClO), cleanly marks border of ozone hole

5. In what parts of the atmosphere is mechanism I?

Middle + upper stratosphere (where ozone concentration is low to start)

Electromagnetic spectrum (not in study Qs)

Mnemonic: Raving Martians Invaded Venus Using Xray Guns Long wavelength, low freq., low E Radio v microwaves v IR (750+) - Thermal IR (3.5-20 um) v Visible (400-750 nm) v UV (50-400 nm) v xrays (<50 nm) v gamma Short wavelength, high freq., high E

11. What is the Montreal Protocol, and what have been the effects of its implementation?

Montreal protocol is an international agreement that made it so all ozone-depleting chemicals are destined to be phased out of use ----------------- Effects 1) All legal CFC production ended by 2010 2) Production of carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) was phased out 6) Production of HCFCs to end in developed countries by 2030 and in developing by 2040 8) Halon production ended in developed countries - use of existing stocks continued - Creation in china and korea increased in 1990s - levelled off now 9) Methyl bromide was supposed to be phased out, but hasn't yet been ----------------- "Total tropospheric concentration of chlorine peaked in 1994, and had declined by about 10% by 2007" - chlorine decreasing - bromine increasing still > some compounds still in use, even if no longer produced Avoided increases in chlorine, which would have been catastrophic Effects 1) Concentrations of phased out compounds hav peaked and begun to decline 2)

10. What happens to the nitrogen dioxide produced by the OH/HOO cycle? What happens to the O atoms produced in the cycling between NO and NO2?

NO2 - Absorbs UV-A from sunlight and photochemically decomposes to NO and O NO2 + UV-A > NO + O O - React quickly with O2 to form ozone - Only source of ozone in the troposphere

15. Why is NOx a problem for diesel engines? What strategies are there for reducing its emissions?

NOx is a problem for diesel engines because they are operated fuel lean - w/ excess oxygen present, so the conditions aren't right for NOx control ---------------- Lowering operating temperature by recirculating some of the gases can reduce NOx produced 1) Gas is completely oxidized to NO2 in fuel lean conditions. The NO2 is then passed over an absorber like barium oxide (BaO), which is then stored briefly as barium nitrate (Ba(NO3)2). - When absorber is saturated, vehicle switches to fuel-rich conditions, reducing NOx to N2 2) Vehicle carries reducing agent *urea* (CO(NH2)2) - It can be injected slowly into a catalyst to react with NOx, converting mixture to nitrogen, water, and carbon dioxide

7. Why can some natural areas (such as the Smoky Mountains) end up with a blue haze over forested regions?

Natural hydrocarbons react in sunlight, without NOx to make carboxcylic acid - these condense and form particles that, when suspended in air, scatter sunlight

1. What are the natural sources of SO2 in the environment? What are the most significant anthropogenic sources?

Natural: - Volcanoes - Oxidation of gases produced by decomposition of plants Anthro - Coal combustion (primary source for SO2) - Coal contains sulfur, which is oxidized to sulfur dioxide during combustion - crude oil + natural gas (in reduced H2S form)

8. What is a naturally occurring gas that can act as X in Mechanism I? How does this gas form? What are the steps in the reaction where it reacts to destroy ozone?

Nitric oxide (NO) Forms when N2O and O* react OH can also act "oh no!" ------------------ Destruction of ozone: NO + O3 > NO2 + O2 NO2 + O > NO + O2 O3 + O > 2O2 (overall) NO as catalyst (only ozone in stratosphere, not troposphere)

7. What is nitrous oxide, and where does it absorb in the IR spectrum? How effective is it as a greenhouse gas?

Nitrous oxide (N2O) - NNO (weird atom - O not in center) Angle-Bending vibration absorbs in 8.6 um (?) (within window region) Stretching vibrations is at 7.8 um (near window + same as one methane absorption) - N-O -NN stretch outside of IR zone, so doesn't contribute ------------ Per molecule - 206 times more effective than, then 114 times as effective on average over a century

6. Is ozone depletion limited to polar and sub-polar regions?

No, but it happens less towards the equator

9. Will a photon with sufficient energy necessarily cause a reaction to occur? Why or why not?

No. 1) Molecules may not absorb the wavelength = no effect 2) When absorbed, energy can be diverted (ex. heat or photons) necessary but not sufficient

14. Is there a similar ozone hole over the Arctic? What factors (both chemical and physical) result in a different pattern of ozone depletion in the Arctic than what is observed in the Antarctic?

No. There is partial depletion sometimes, but it's less severe Reason 1) Stratospheric temp does not get as low 2) Colder temp doesn't last long 3) Air circulation to surrounding areas not limited (can circulate and warm) As a result, polar stratospheric clouds form less often and for less time

12. What factors affect the atmospheric lifetime of CO2? What permanent sink(s) are available? How should the effective atmospheric lifetime of CO2 be considered?

Not decomposed chemically or photochemically Factors ... (pg 181) Permanent sinks 1) Dissolution in deep water/ocean 2) Precipitation in deep ocean/water as insoluble calcium carbonate -------------------- Effective lifetime - Think about new CO2 fossil-fuel emissions being quickly allocated among air, shallow ocean, and biomass (with interchange between them) > temporary - then slowly, over decades/centuries, almost all the new CO2 will enter the final sink (deep ocean) ~ 50-200 years to adjust to new equilibrium concentration if a source of it increases - *so long effective lifetime (decades or centuries)*

11. What is the prevalent form of oxygen in the stratosphere? Why is this different than the regions higher up? What does this mean for the fate of atomic oxygen in the stratosphere?

O2 Bc there is less UV-C light and molecular concentration is higher Likely to react with diatomic oxygen molecules, making Ozone

12. What is the reaction for the formation of ozone in the stratosphere? How does the top of the stratosphere differ from the bottom of the stratosphere in terms of the amount of UV light and the concentration of O2? What does this mean for where ozone formation takes place?

O2 + photon > 2 O --------- O + O2 + M> O3 + heat + M - M = N2, H2O, or O2 - source of all ozone in stratosphere Top - less O2, more high E UV (UV-C) Bottom - greater O2 (denser air) less high-E UV (UV-C This means that more ozone creation takes place in 15-35 km (aka *ozone layer* / stratosphere) because of the limiting conditions at top and bottom - middle to lower stratosphere

10. Why does no UV light with a wavelength shorter than 220 nm reach the earth's surface?

O2 above the stratosphere filters UV from 120-220 nm - O2 in stratosphere filters the rest in this range O2 above stratosphere and other air molecules (i.e. N2) filter wavelengths shorter than 120 nm

9. Which wavelengths (give a range) of light does O2 absorb most strongly? What about a molecule causes the characteristic absorption spectrum?

O2 absorbs ~70-250 nm - absorbs most UV light in 120-220 nm ... *absorption spectrum* = graphical representation that shows relative fraction of light absorbed by a given type of molecule as a function of wavelength Structure of molecule + energy level of electrons determines absorption spectrum

16. By what reaction is ozone destroyed by interaction with atomic oxygen? Why does this reaction not always occur when O3 collides with O?

O3 + photon > O* + O2* or O2 + photon (UV) > 2O + O3 + O > 2O2 - High activation energy, so inefficient ---------- Doesn't happen always because it has a high activation energy. So even if they do collide, they lack energy to react

20. Why is the term "ozone layer" something of a misnomer?

O3 is not the most abundant gas or oxygen-containing species, even in the ozone layer

9. How does this cyclic mechanism apply to other trace gases? What common gases is hydroxyl radical not reactive with?

OH initiates oxidation of almost *all* reduced gases OH unreactive towards - molecular oxygen (O2) - molecular Nitrogen

8. How was the synthesis of ibuprofen improved to increase its atom economy?

Original boots synthesis: - Multistep process, atom economy of 40% - Lots of stoichiometric + auxiliary (?) reagents that contribute to waste ----------- BHC synthesis 1) Eliminated auxiliary materials (prin 5) 2) Reduced number of steps from 6 to 3 3) Increased atom economy to 77% - HF, Raney nickel, and Pd are used in catalytic amounts 4) Byproduct from step 1 (acetic acid) isolated and used as a desired product, increasing atom economy to 99+% - Higher yields

6. Why do all VOCs (rather than just alkenes and aldehydes) need to be limited in regions with smog issues?

Other VOCs (hydrocarbons w/o double bonds) become significant after first few hours of smog bc *concentration of free radicals has risen*

Which have been harder to reduce?

Ozone

17. What is the Chapman mechanism/cycle?

Ozone production/destruction process UV-C in stratosphere produces O atoms from O2. These collide with other O2 to form ozone O2 + photon (UV-C) > 2O O + O2 + M> O3 + heat + M - M = N2, H2O, or O2 ----------- Destroyed when absorbing UV-C or UV-B O3 + photon > O* + O2* or O3 + O > 2O2 Ozone is constantly formed/decomposed/reformed

16. How are particles from diesel engines limited?

Particle traps - Can filter ~90% of small-particle emissions, reducing the amount of exhaust particles - Have to be cleaned though Homogenous charge compression ignition (HCCI) engine - New internal combustion engine that combines gasoline and diesel tech - Mixes fuel and air before ignition, preventing soot particle formation - High compression of air-fuel mix allows combustion in many locations in cylinder, which is more efficient and reduces CO2 emissions

18. Why were initial predictions about the rate of chlorine-catalyzed destruction of ozone too high?

People didn't know that 99% of stratospheric Cl was inside inactive forms

14. What pollutants do wood-burning stoves contribute to the air? How has design of these stoves changed to make them more efficient?

Pollutants: - fine particles ... (124) ----------------- Design: 1) Catalytic converter - a coated ceramic honeycomb-structure. Placed near the top of the firebox so that, when smoke rises, it is oxidized more fully before escaping 2) Secondary combustion of smoke near top of fire box - some air from stove diverted through tubes under and around the fire, rea-heating it - hot air released near top of box, where the smoke combusts - baffle diverts air (smaller exit opening/longer route) to make smoke stay in secondary combustion zone longer

18. What is positive feedback? What is negative feedback? How can these concepts be applied to the greenhouse effect?

Positive feedback - *a phenomenon produces a result that also amplifies (speeds up/increases) the result* - Increase in [water vapor] due to global warming (increased CO2, etc) makes more global warming due to H2O (g) comparable to combined original amount due to the other greenhouse gases > water vapor then heats the atmosphere, reinforcing itself Negative feedback - A system that reduces level of output (slows/ decreases)

14. What is the difference between primary pollutants and secondary pollutants?

Primary pollutants - Emitted directly into air - NO and VOCs - Generally nontoxic Secondary pollutants - Substances that primary ones transform into after reacting - Ozone, *nitric acid* (HNO3), partially oxidized/nitrated organic compounts - More toxic than reactants

How is this replacement consistent with the principles of green chemistry?

Principle 3 - substance is less toxic to the environment (ozone specific) Principle 4 - increases efficacy while reducing toxicity Principle 10 - breaks down into more innocuous degredation products Principle 12 -nonflammable, so minimizes potential for chemical accidents (fire)

2. In which region of the globe is ozone produced? Where is it then moved by stratospheric winds? What is a typical ozone concentration (in DU) for the tropics? For sub-polar regions?

Produced in the tropics Moved to polar regions Typical concentration in tropics = 250 DU Subpolar regions = 450 DU

8. What is the purpose of a catalytic converter? What is the difference between a two-way and a three-way converter?

Purpose: - To control NOx emissions - Reduce primary pollutants from exhaust Exhaust passed over Pt (platinum) and Rh (rhodium) catalysts Two way: - Control *only carbon-containing gases* (ex. CO) by completing combustion to CO2 Three way: - Changes *nitric oxides* back to elemental nitrogen + oxygen using unburned hydrocarbons and combustion intermediate (CO + H2) as *reducing* agents - Also catalyzes *oxidation* incompletely oxidized C- compounds to CO2

8. How is the rate of energy release by a blackbody related to its temperature?

Rate of emission is temp sensitive, so: the warmer a body, the more energy it emits per second ------- rate of energy release as light by a blackbody increases in proportion to fourth power of its Kelvin temp Stefan-Boltzmann Law rate of energy release = kT4 rate increases significantly w/ temperature k (aka sigma o) = proportionality constant

2. What is the redirection of light by particles called? What effect does this redirection have on the temperature of the air and the surface below the reflecting aerosol?

Redirection of light by particles = *scattering* - reflection backwards is back scattering Effect on air temp + surface temp: - prevents that light from being absorbed on the surface - reflection of sunlight cools air mass and surface below it (since none is absorbed and converted to heat)

1. What must be done to improve air quality in cities? Why does reduction of hydrocarbon emissions not have as large an effect as might be hoped?

Reduction of NOx, hydrocarbons with C=C bonds, and other reactive VOCs Hydrocarbon emmission reduction common, but not as effective because initially, hydrocarbons are overabundant relative to nitrogen oxides - Reduces excess but doesn't slow down the rxns significantly - Nitrogen oxides are the limiting reactants

8. What effect does rotational energy have on the wavelength a given molecule will absorb?

Rotational energy = energy associated with rotation (tumbling) of molecule around its internal axes When IR light is absorbed, rotational energy can increase/decrease slightly, increasing vibrational energy - so photon absorption occurs at slightly higher/lower frequencies corresponding to the vibration Creates an "absorption band" - multiple wavelengths that CO2 can absorb

6. What is the runaway greenhouse effect and what could cause it? Why would it be problematic?

Runaway greenhouse effect - unstoppable warming of earth - Cause: some positive climate feedback mechanism (including ones with methane) Problem bc: - temp would rise, ocean currents would shift, rainfall patterns would change) - North Atlantic ocean current that brings warm water from south (warming Europe) would stop

7. How can you judge if a molecule is likely to absorb IR radiation?

See number of atoms + atom identity. Molecules w/ 3+ generally have some vibrations that absorb IR - have bend 1) Symmetric, nonpolar molecules have bending + asymmetric (aka antisymmetric) vibrations 2) Polar molecules - have symmetric vibrational modes (ex. water) - 2 atom molecules w/ different atoms will have dipole movements, and can absorb (ex. NO, CO) ------------ ex. CO2 - linear symmetric molecule, but absorbs IR during bending and asymmetric stretching - No absorption during symmetric stretching

2. What is the atmospheric lifetime of methane? How does this compare to the lifetime of CO2?

Shorter - less than a decade

11. What is ozone's significance as a greenhouse gas? How does the atmospheric lifetime of ozone affect its contribution to the greenhouse effect?

Significance as GH gas: - *symmetric-stretching vibration (atmospheric window region 9-10 um)* - bending vibration ~14.2 um, but this doesn't contribute much bc CO2 is already absorbing most of that - antisymmetric-stretch = 5.7 um, but there is little outgoing IR there Atmospheric lifetime contribution: - has a short tropospheric life, but locally can absorb IR ~10% of global warming estimated

1. What is a "sink" in an atmospheric context, and why is it important when considering what compounds contribute to ozone depletion?

Sink = a natural removal process - Ex. Dissolution in rain (goes down w/ rain), oxidation in troposphere Important because they don't break down, and can travel through the troposphere to reach the stratosphere - Releases halogen atoms for ozone breakdown (ex. Cl- and Br-)

3. What are the atmospheric sinks for methane? What effect do these sinks have on global warming?

Sinks *1) Reaction with hydroxyl (OH)* in troposphere (dominant ~90%) - oxidation (has lots of H for attack) CH4 + OH > CH3 + H2O Goes on to be transformed to CO2 ( CH4 >> CH2O >> CO >> CO2) *2) REaction with soil* *3) Loss to stratosphere* - reacts with OH/Cl/Br/O* (excited) - rxn with O* makes hydroxyl radicals and (eventually) water molecules O* + CH4 > OH + CH3 or OH + CH4 > H2O + CH3 ---------------- Effect Loss to stratosphere increases global warming effect of water vapor (~25% of methane-caused warming)

13. What sinks are available for CO2 released from anthropogenic sources? What is the general trend of the fraction of CO2 absorbed by a sink as a function of time?

Sinks - ocean absorption - Upper layers of ocean (principle sink) - forest growth/soil storage (sedimentation) Trend - less than half anthro CO2 emissions are quickly removed (over short + medium term) gas accumulates in atmosphere - There has been a growth in total emissions, and the uptake by the ocean/land is not keeping up

2. How is SO2 produced during smelting processes? How can the SO2 produced during these processes be converted to a commercial product?

Smelting => ores converted to free metals - many valuable ores also contain *sulfide ion (S2-) 1) Originally roasted in air to remove sulfure, which is converted to SO2 and released into air - high amount of SO2 waste, but easy to extract - ex. 2NiS(s) + 3O2 (g) > 2NiO(s) + 2SO2(g) 2) Pass gas over oxidation catalyst, converting SO to sulfur trioxide. Adding water to this creates *sulfuric acid* (H2SO4) (viable commercial product) - 2 steps in 2nd rxn reduce waste created - ex. 2 SO2 (g) + O2 (g) > 2SO3 (g) v SO3 (g) + H2O (aq) > H2SO4 (aq) (2 step rxn, not shown) - first trioxide is combined w/ H2SO4, then water is added

9. What happens to the thermal IR light emitted by Earth? Why does not all of it escape to space?

Some gases in atmosphere absorb it (at certain wavelengths) Because of this, not all of the IR emitted escapes to space

What sources are responsible for recent increases in atmospheric methane concentrations? What forms of methane emission could result from positive feedback as the Earth warms?

Sources responsible for atmospheric CH4: 1) Plant decay - in wetlands/swamps - increase in rice production - seasonal fluctuation - higher temp accelerates biomass decay (positive feedback) > melting of arctic permafrost, which trapped CH4 *(positive feedback)* > releases methane + frozen plant decays 2) Expansion of wetlands from deliberate flooding to make more hydroelectric power - not this, but frozen bog melting can contribute to more warming (positive feedback 3) Anaerobic decomposition of organic matter in landfills (esp. food waste) - higher temp accelerates biomass decay (positive feedback) 4) Burning of biomass - makes both methane and CO2 (more dominant) 5) Ruminant animals (cows/sheep/goats) 6) Natural gas pipeline leaks, coal mining that releases trapped CH4, and release of gases dissolved in crude oil *Positive feedback (2nd main)* - Clathrate compound (CH4*6H2O) forms under high temp + low pressure - result in ice that can be burned as you burn methane - methane could be released due to melting (192))

5. What are the major emission sources for methane?

Sources: ~70% anthropogenic in origin 1) Energy production 2) Agriculture 3) Waste disposal 4) Plant decay - mostly from *anaerobic decomposition* (Cellulose (CH2O) >> CH4 + CO2) - waterlogged conditions NAtural (~30%) 1) anaerobic decomposition of plant matter in wetlands/swamps - 2CH2O >> CH4 + CO2 - swamp = largest natural source ------------ order energy production/distribution ~ ruminant animal livestock > rice production ~ biomass burning ~ landfills

14. What is a "steady-state" concentration of a gas, and what influences the steady-state of ozone concentration? Can ozone in the stratosphere ever be completely eliminated?

Steady-state - When the net rate of destruction meets the rate of production - Ozone steady state influenced by ozone concentration times sunlight intensity (UV-B) or catalyst concentration (X) -------------- Cannot be permanently/totally destroyed - due to constant reformation rxns

12. What are the sub-steps in the reaction of two chlorine monoxide free radicals to form dicholoroperoxide and subsequently release atomic chlorine and O2? Why does this cycle require cold temperatures? 13. What is the rate-limiting step in the sub-steps listed above. What does this mean for the rate of catalytic destruction of ozone via Mechanism II with Cl or another X and X' catalyst?

Step 2a: 2ClO > Cl-O-O-Cl - ClOOCl = dichlorine peroxide Step 2b: ClOOCl + UV light > ClOO + Cl - Insufficient light until early spring Step 2c: ClOO > O2 + Cl - Doesn't need light to decompose ------------------ Net: 2ClO > [ClOOCl] > 2Cl + O2 light as seen in mechanism II ----------------- Rate limiting step: 2a - rate dependent on proportion of ClO. Destruction of ozone is significant when ClO is high ClOOCl isn't stable, so needs low temp or else it'll break into 2ClO

Suggested problems Ch 1: In-text Problems 1-1 and 1-2 In-text Problems 1-6, 1-8, Box 1-3 Problem 1 End-of-Chapter Additional Problems 2, 3, 5 ----------------- Suggested problems ch 2 End of Chapter Additional Problem 1 Box 2-1 Problem 1, In Text Problems 2-1 and 2-3 In text problems 2-4, 2-5, and 2-6, End of Chapter Additional Problems 2 and 3 -----------------

Suggested problems ch 3 In-text Problems 3-1 and 3-2, Additional Problems *2* and *5* Suggested Problems: In-Text Problems 3-5, 3-7 and 3-9 In-Text Problems 3-10 and 3-15, End-of-Chapter Additional Problem *7* ----------------------- Suggested Problems: In text Problem 5-1 In-text Problems 5-2, *5-4*. and *5-6*, End of Chapter *Additional Problems 2 and 3* In text Problem 5-9, End of Chapter Additional Problem 8

15. What is the dominant source of sulfuric acid droplets in the lower stratosphere? How does ozone contribute to denitrification of the lower stratosphere by these drops? Mid latitude ozone depletion

Sulfur dioxide gas emitted from volcanoes, which gets oxidized to H2SO4 ----------------- Denitrification: - Ozone converts nitrogen dioxide into nitrogen trioxide, which converts other NO2 to dinitrogen pentoxide (N2O5) NO2 + O3 > NO3 + O2 NO2 + NO3 > N2O5 These are usually reversible, but cold sulfuric acid droplets allow for denitrification N2O5 + H2O > 2HNO3 - More Cl catalytically active, bc no longer trapped

13. Why is sunlight necessary for photochemical smog?

Sunlight indirectly increases concentration of free radicals that participate in chemical processes of smog - Photodecomposition rxn necessary for high free radical concentrations (needed as catalysts)

1. How is sustainable development defined in the Brundtland Report?

Sustainable development: - "Development that meets the needs of the present w/o compromising the ability of future generations to meet their own needs" - Fulfill present needs in a way that doesn't deprive resources, etc. needed in future - Taking care of the environment! Needs = clean water, safe place to live, ability to get food Focus areas (the triple bottom line) 1) Society 2) Economy 3) Environment

10. What effects does this ozone depletion have on ozone concentrations in populated areas in the Southern Hemisphere?

Temporarily lowers ozone levels in places like australia, new zeland, and southern south america - HAppens before ozone levels are able to build up bc ozone poor air mixes w/ normal air Ex. Australia has high skin cancer rates

13. What is the major environmental concern relating to the depletion of ozone?

The entry of more UV-B light, which has harmful effects in a variety of areas and isn't absorbed as well as UV-C

14. What is responsible for the temperature in the stratosphere being higher than in the air above and below it? What is temperature inversion? Why does this occur in the stratosphere but not the troposphere?

The ozone reaction, which releases heat *temperature inversion* = air at a given altitude is cooler than the air above - cool air should be lower due to higher density than hot Troposphere has faster mixing of air - sun heats ground (and air touching it)

5. What is necessary for infrared light to be absorbed by a molecule during a vibration?

There must be a difference in the position of a molecule's center of positive charge (nuclei) and negative charge (electron cloud) at some point during the motion *aka. it needs a change in dipole moment (polarity with direction)* Diatomic molecules like Ar, O2, and N2 have homonuclear centers of charge, so they always have dipole moments of 0 = no absorption of IR light

7. What is thermal infrared radiation? What wavelengths are in this region?

Thermal infrared radiation - 5-100 um range - energy that is in form of heat

4. What are polar stratospheric clouds, and why do they form?

They form because gases condense inside a vortex, due to the cold temps and isolation of air particles inside - can't mix PSCs are made of *water, sulfuric (H2SO4), and nitric acids (HNO3)* (forming small initial crystals) When air temp drops further (below -80 degrees C), larger crystals made of frozen *water*, ice and *nitric acid* (HNO3), form It's on the aqueous surface layer of PSC ice crystals that rxns related to ozone destruction happen

3. What happens to CFCs when they get to the middle and upper stratosphere? Why is this important?

They photochemically decompose, releasing chlorine atoms - Because there is enough UV-C light Important bc it contributes to breakdown of ozone

2. How do energies of light in the UV/Visible regions compare to the enthalpies of chemical reactions?

They're on the same order of magnitude as the enthalpies (heat (ΔH°)) changes of chemical reactions

24. What is NOx? What natural sources are there of NOx compounds? What are the anthropogenic sources?

Together, NO and NO2 in air = NOx NAtural sources - Lightning flashes - Ammonia + NOx release - Coniferous trees where exposed to sunlight + when these gases are low Anthropogenic sources - Off road vehicles - On road vehicles - Electrical generation - Non industrial - Industrial

3. How is the term "Tragedy of the Commons" defined? Why is this an important concept in environmental chemistry?

Tragedy of the commons: - Economic theory by Garrett Hardin - If a resource is available to everyone (common) it will be depleted entirely because rational people are self-interested (don't care if they don't own it) > No one has responsibility, so it will be consumed > Bad for all Importance (...?) Certain people (towards the bottom) can't use the resource. + Others dump waste into commons, which affects more than them

5. Why do urban areas that are bordered by heavily wooded areas need to limit NOX emissions to limit smog?

Trees emit enough reactive hydrocarbons (VOCs) to sustain smog/ozone production, even w/o anthropogenic hydrocarbons There will always be some VOC, so the only thing that can be done is *to limit NOx* (thus reducing ozone)

7. What are the trends in sulfate aerosol concentration? What effects do the sulfate aerosol have on the appearance of global warming?

Trends - Increase of global SO2 over the last century and a half (200) Effects on appearance: - SO2 emissions are postponing the full effects of global warming induced by rise in GH gas concentrations

3. What types of particles can absorb (rather than just reflect) significant amounts of light? How are the global effects of these particles different than the local effects?

Types of particles that can absorb, rather than reflect, light: - some types of aerosol particles - significant for dark-colored particles aka. *black carbon* (ex. made mostly of soot, or ash from volcanoes) --------------- Global vs. local effects > When they absorb light, they exchange heat with nearby molecules thru collisions. > This warms air immediately around it Global - short atmospheric lifetime (weeks) - Increase air temps through absorption of sunlight (air goes to other areas) Local: - Cools, since it blocks sunlight from surface

17. What units are used to measure the energy inputs to the Earth? How much energy (in these units) is input by the sun from the outside of the atmosphere? How much of this is absorbed into the atmosphere and surface? How much must be re-emitted by the surface and by the atmosphere for Earth to maintain a constant temperature?

Units - Watts (joules per second) per square meter of surface Sun inputs 342 (W m^-2) 235 (W m^-2) is absorbed by atmosphere - this much energy must be re-emitted to space for planet to maintain a steady temperature (normally) > bc of greenhouse gasses, this amount of emission is not sufficient (so 390 W m^-2 are needed...? (174)

15. What is an approximate overall reaction for the smog reaction?

VOCs + NO + O2 + Sunlight >> Mixture of O3, HNO3, organics Primary pollutants >> secondary pollutants

12. What are VOCs? What are the sources of VOCs?

VOCs = substances that readily vaporize into air (ex. hydrocarbons + derivatives) Sources -Evaporation of solvents, liquid fuels, and organic compounds, partial/incomplete coombustion

15. When IR is emitted by the Earth, how likely is it to escape directly into space?

Very little likelihood - absorbed by air close to ground and then re-emitted

8. What are the most significant anthropogenic sources of global warming and cooling? What is the relative contribution of each? Which has the largest uncertainty?

Warming: 1) CO2 ~ 90% 2) CH4 - ~30% includes warming from additional water vapor by CH4 decomposition 3) O3 (tropospheric) - ~ 25% 4) CFCs - includes cooling of stratosphere induced by their destruction of ozone - ~ 19% 5) N2O - ~10% Solar also warms a little ------------- Cooling 1) Aerosols ~ 80% - cancels out around 40% of warming from all greenhouse gases - aerosol effect (sum of direct and indirect effects affecting cloud albedo) has *largest uncertainty* 2) Surface albedo - change in land use minus warming from deposition fo sunlight-absorbing black soot on snow/ice - ~ 5%

Green chemistry definition (not in study guide) + Principle groups

Way of designing chemical processes so that hazardous chemical creation/use is reduced Aims: 1) REduce waste (esp. toxic waste) 2) Reduce energy consumption 3) Reduce resource consumption/use renewable resources ----------- Groups of green chemistry principles A) Prevention of pollution - 1 B) Materials used + products formed - 2-5, 7-10, 12 C) Minimization of product/material toxicity - 3 + 4 D) Energy requirements - 6 E) Monitor to prevent creation of toxins - 11

5. Why is it advantageous to replace CFCs with CO2 as a blowing agent for polystyrene foam?

When CFCs are used, crushed/degraded foam releases CFCs which can destroy ozone in the stratosphere CO2 doesn't deplete ozone and is nonflammable (Safer) - Waste CO2 can be captured and used in this process CO2 blown foam stays flexible for longer than CFCs - less breaks, longer shelf life - Leaves easily, so can be recycled with less processing

12. What is the enhanced greenhouse effect? Why is it of concern?

When concentration of the trace gases in the air that absorb thermal IR are increased, more thermal IR is absorbed and converted to heat This could increase the temp

1. Under what circumstances is a given wavelength of light most likely to be absorbed by a molecules?

When the light frequency almost matches exactly with frequency of internal motion of the molecule

Ch 5 problem 5-9 Fully flurinated compounds such as tetrafluoromethane and hexafluoroethane are released as by-product wastes into the air in the production of aluminum Will such molecules have a sink in the troposphere? Will they act as greenhouse gases? Would your answers be the same for monofluoromethane and monofluoroethane?

Will such molecules have a sink in the troposphere? - no, because they don't have any C-H or multiple bonds that can be attacked by OH - not soluble in water and doesn't absorb UV or visible light (due to not having multiple bonds) Will they act as greenhouse gases? - Yes, because C-F stretch and FCF bending vibrations are in the thermal region (less efficient than CFCs) Would your answers be the same for monofluoromethane (CH3F) and monofluoroethane (C2H5F)? - would be attacked by OH (has sink) - Would also act as greenhouse gases still problematic as GH gases

7. Has there been any reversal in the ozone losses in the 1980s and early 1990s? Where is this recovery taking place? pg 40

Yes. It recovered in the northern and southern hemispheres (especially near the poles) - Hasn't cancelled out loss before though

28. Does the ozone cause problems in places other than where it's generated? Why?

Yes. It's a regional (not local) problem Hot summertime conditions do not allow vertical mixing of air, allowing them to travel far

5. What are the 12 Principles of Green Chemistry? For each principle, what is an example of how a process could be changed or improved to address that principle?

direct quotes 1) It is better to *prevent waste* than to treat or clean up waste after it is formed - Preventative vs. end-of-pipe solution - Change: Plan process so that less waste is made 2) Synthetic methods should be designed to *maximize the incorporation* of all materials used in the process into the final product - Want to be efficient in that as much stuff that goes in as possible comes out - Change: Look for more efficient synthesis routes 3) Wherever practicable, synthetic methodologies should be designed *to use and generate substances that possess little or no toxicity* to human health & the environment - Don't want toxic waste - Change: ... 4) Chemical products should be designed to *preserve efficacy of function while reducing toxicity* - should still serve function, but with less toxic products > Can't eliminate toxicity entirely! - Change: ... 5) The use of *auxillary substances should be made unnecessary* whenever possible and innocuous when used - auxillary = substances that aren't going to be incorporated into final product. Part of processes, but want less + less harmful 6) Energy requirements should be recognized for their environmental and economic impacts, and should be minimized. Synthetic *methods should be conducted at ambient temperature and pressure* - Reduce energy consumption (fossil fuel uses) - Change: Conduct processes at Room temp + atmospheric pressure 7) A *raw material feedstock should be renewable* rather than depleting whenever technically and economically practical - Material put into synthetic process - Ex feedstock. things derived from petroleum processes - Change: Replace petroleum with plant derived/extracted feedstock (which is renewable) 8) Unnecessary *derivatization* should be *Avoided whenever possible* - Ex Derivatization = protection of undesired functional groups, changing a functional group - Change:... 9) *Catalytic reagents* are superior to stoichiometric reagents - Catalyst can be used repeatedly. Stoichiometric used up with each production - Change:... 10) Chemical products should be designed so that at the end of their function they *do not persist in the environment* and instead break down into innocuous degradation products - Shouldn't stick around - Change: DDT (persists + toxic) replacement by... 11) Analytical methodologies should be further developed to allow for *real-time, in-process monitoring* and control prior to the formation of hazardous substances - Need to be able to monitor process real-time to prevent production of hazardous substances - Change: ... 12) Substances and the form of a substance used in a chemical process should be chosen so as to *minimize the potential for chemical accidents*, including releases, explosions and fires - Change: Choose less dangerous substances, choose a different storage method, use more stable forms of substances

9. What are the variables in the Arrhenius equation? How can this equation be used to examine the effect of temperature on reaction rate?

k = A e^(-E/RT) k = rate constant E = activation energy (joules/mole) R = 8.3 J/(K mol) A = (same units as k) Can calculate k for a given temperature - shows that k (reaction rate) increases with T

13. Why doesn't ozone formation by this mechanism continue as altitude decreases?

less UV light penetrates = O2 not formed below stratophere

7. Where does the energy involved with ozone depletion come from?

light from the sun

5. Why is molarity rarely used when describing the absolute concentration of a gas?

molarity = moles per liters Not used because gases are too dilute

Sketch (roughly) the temperature profile of the lower atmosphere, and indicate where each region begins and ends. (FYI, the region above the stratosphere is called the mesosphere).

see notecard pile or pg. 4

10. What is sulfurhexafluoride, and what is it used for? What is its significance as a greenhouse gas?

sulfurhexafluoride (SF6): - a greenhouse gas - good absorber of thermal IR (~10.5-11 um) in atmospheric window - 23,900 times greater than CO2 - long lived in atmosphere (~3200 years) Used for: -used as an insulating gas by electric utilities and semiconductor industry - used to be vented, but is now recycled Significance as GH gas: - high potential to be GH gas - concentrations have been increasing

14. How can we approximate the effect of greenhouse gases on the Earth's temperature?

temp of Earth w/o greenhouse gases = 255K rate of emissions would be k(255)^4, which would be equal to rate of energy input from sun Real earth acts like 60% of that E is absorbed, leading to: 0.6kT^4 = k(255)^4 v T= 290 K Suggesting that earth's temp is 17 degrees C, indicating increase of 35 degrees (from original temp of -18) if we increase green house gases ------------ however, bc of reabsorption, surface must emit MORE energy than comes in from sun to maintain temperature