Chapter 15: Major Air Pollutants and Their Sources
Size of Particulate Matter
- PM in the atmosphere ranges considerably in size and can absorb or scatter light, creating a haze and reducing the light that reaches Earth's surface - PM is categorized by how big it is - ranges in size from 0.01 micrometer to 100 µm (human hair has a diameter of 50-100 µm) - PM larger than 10 µm is filtered out by the nose or throat and not regulated by the EPA - PM smaller than 10 µm are called Particulate Matter-10 (PM10) - PM10 are of concern to air pollution scientists because they are not filtered out by the nose and throat and can be deposited deep within the respiratory tract - PM of 2.5 µm and smaller (PM2.5) are even more dangerous because they can travel further within the respiratory tract and tend to be composed of more toxic substances
Carbon Monoxide (CO) Effects
"criteria pollutant" - causes headaches in humans at low concentrations - silent killer, bonds to hemoglobin in red blood cells, thus preventing oxygen from binding to the hemoglobin and interfering with oxygen transport in the bloodstream - can cause death with prolonged exposure at high concentrations
Nitrogen Oxides (NOx) Sources
"criteria pollutant" - combustion in the atmosphere, which is 78% nitrogen gas (N2), leads to the formation of nitrogen oxides - motor vehicles and stationary fossil fuel combustion (power plants, burning fossil fuels) are the primary anthropogenic sources - all combustion in the atmosphere including wood and other biomass burning - natural sources include forest fires, lightning, and microbial activity in soils
Ozone
- "Ozone is good up high, bad nearby" - ozone is found in two regions of the Earth's atmosphere: the troposphere and the stratosphere - in both regions, ozone has the same chemical composition (O3) - in the stratosphere, ozone protects us from the sun's harmful UV radiation/rays by absorbing UV light so it does not reach humans and cause cell death, skin cancer, and eye damage (cataracts) - UV light is harmful to all living things (contributes to the wilting a death of vegetation) - in the troposphere (where we live), ozone is an oxidant that can harm respiratory systems in animals and damage several structures in plants - ozone is a key component of smog; it also damages trees and plants
Particulate Matter (PM) Sources
- "criteria pollutant" - (PM): solid or liquid particles suspended in the air - PM can be natural or anthropogenic - produced by the combustion of wood, animal manure and other biofuels, coal, oil, and gasoline/diesel - most commonly known as a class of pollutants released from the combustion of coal/oil - diesel-powered vehicles give off more particulate matter, in the form of black smoke, than gasoline-powered vehicles - PM can also come from road dust and rock-crushing operations (construction) - agriculture and other activities that mobilize soil, soot, and dust - volcanoes, forest fires, and dust storms are important natural sources - wildfires can worsen air quality and produce a hazy orange sky
Sulfur Dioxide (SO2) Sources
- "criteria pollutant" - a corrosive gas that comes primarily from the combustion of fuels that contain sulfur such as coal, oil, and gasoline - all plants and animals contain sulfur in varying amounts, so the fossil fuels derived from their remains contain sulfur - when these fuels are burnt, like coal, the sulfur combines with oxygen to form sulfur dioxide - released in large quantities during volcanic eruptions and in much smaller quantities, during forest fires
Ozone (O3)
- "criteria pollutant" - a secondary pollutant made up of three oxygen atoms bound together - combination of sunlight, water, oxygen, VOCs, and NOx - harmful to both plants and animals - reduces lung function and exacerbates respiratory symptoms - a degrading agent to plant surfaces - damages materials such as rubber and plastic - the average ozone concentration for any 8-hour period should not exceed 0.075 parts of ozone per million parts of air by volume more than 4 days per year, averaged over a 3-year period
Lead (Pb) Sources
- "criteria pollutant" - lead is a trace metal that occurs naturally in rocks and soils - also sourced from lead-based paint in older buildings, produces dust and chips when the paint peels off - present in small concentrations in fuels including oil and coal - lead compounds were added to gasoline for many years to improve vehicle performance - during this time, lead compounds released into the air traveled with the prevailing winds and were deposited on the ground by rain or snow - they became pervasive around the globe, including in polar regions far from combustion sources - phased out as a gasoline additive in the United States between 1975 and 1996, and since then its concentration in the air has dropped considerably - average blood lead levels have also decreased steadily
The Montreal Protocol on Substances That Deplete the Ozone Layer
- 24 nations in 1987 signed the protocol - it is a commitment to reduce CFC production by 50% by the year 2000 - the most far-reaching environmental treaty to date, in which global CFC exporters like the United States appeared to prioritize the protection of the global biosphere over their short-term economic self-interest - today, all 196 United Nations members have signed a series of increasingly stringent amendments that required the elimination of CFC production and use in the developed world by 1996 - the protocol addressed a total of 96 ozone-depleting compounds - the ozone layer will not return to normal levels until 2075
Household Air Pollution in Developing Countries
- 3.8 million die prematurely from household air pollution from cooking by using kerosene and sold fuels with polluting stoves, open fires, and lamps - the fuel that is used for cooking and heating - in very poor communities they use wood to heat their home and have poor ventilation - the fire creates a lot of smoke and releases particulate matter which hangs around inside and affects those who live there - contributes to a lot of really adverse health effects (stroke, heart disease, lung cancer, and pneumonia) - Women and children are at the most risk of being affected by this pollution
Electricity Generation
- 30% of electricity generation is fueled by coal - the major source of anthropogenic sulfur dioxide
Clean Air Act
- Since 1970, the goal of the Clean Air Act has been to reduce the amount of pollution in America's air - requires that the EPA establishes standards to control pollutants that are harmful to "human health and welfare" - human health: human population, including the elderly, children, and those with asthma - welfare: refers to visibility, the status of crops, natural vegetation, animals, ecosystems, and buildings - The Act created the National Ambient Air Quality Standards (NAAQS), which sets a concentration that should not be exceeded over a specified time period - Six major "criteria" pollutants are regulated: -NO2 -SO2 -Ozone -CO -Lead -Particulate Matter (PM) - volatile organic compounds and mercury, though not officially listed in the Clean Air Act, are commonly measured air pollutants that have the potential to be harmful
Criteria Air Pollutants
- Sulfur Dioxide (SO2) - Nitrogen Oxides (NOx) - Carbon Monoxide (CO) - Particulate Matter (PM10, smaller than 10 micrometers, PM2.5, 2.5 micrometers and less) - Tropospheric Ozone (O3) - Lead (Pb)
Air Pollution Regulations
- The Environmental Protection Agency (EPA) has regulatory authority over the air standards - each state is obligated by law to meet the NAAQS - areas that do not meet the standards are called "non-attainment" areas (states can have federal money withheld if they don't meet the standards) - when EPA finds that a violation has occurred, the agency can: 1. issue an order requiring the violator to comply 2. issue an administrative penalty order (use EPA administrative authority to force payment of a penalty) 3. bring a civil judicial action (sue the violator in court)
Anthropogenic Sources of Air Pollution
- Vehicles - Power plants - Industrial processes - Waste disposal
Other Major Air Pollutants
- Volatile Organic Compounds (VOC) - Mercury (Hg) - Carbon Dioxide (CO2)
Natural Sources of Air Pollution
- Volcanoes - Lightning - Forest fires - Plants (both living and dead) - Large nonindustrial areas such as agricultural fields give rise to particulate matter when they are plowed (Dust Bowl of the 1930s) **harder to monitor, regulate, and control
Spring 1998 in the northern Chinese city of Tianjin
- a cold spell occurred after the city shut off its district heating system for the season - resulted in many households using individual coal-burning stoves for heat - a temperature inversion trapped the carbon monoxide and particulate matter from the coal used in these stoves and caused over 1,000 people to suffer carbon monoxide poisoning or respiratory ailments from the polluted air - 11 people died
Sulfur Dioxide (SO2) Effects
- a respiratory irritant - can exacerbate asthma and other respiratory ailments - SO2 gas can harm stomates and adversely affect other plant tissue - converts to sulfuric acid in the atmosphere, harmful to aquatic life and some vegetation
Living plants release
- a variety of VOCs, including ethylene and terpenes - the fragrant smell from conifer trees such as pine and fir and the smell from citrus fruits are mostly from terpenes which can be precursors to photochemical smog and oxidant pollution
Ways to Prevent Air Pollution
- Avoid emissions in the first place (improve public transportation, reduce the amount of electricity used, encourage the purchase of electric cars) - Use cleaner fuel (more nuclear power plants, solar panels, more natural gas power plants as opposed to coal-burning power plants) - Increase efficiency (cars that get more miles per gallon, LED light bulbs) - Control pollutants after combustion
Major Air Pollutants
- EPA calls these pollutants "criteria" air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels
Reducing Nitrogen Oxides
- Earth's atmosphere is 78% nitrogen gas - therefore, almost all combustion processes produce nitrogen oxides - proportionally more nitrogen oxide per unit of fuel burned is produced in the presence of oxygen and hotter burning conditions - reducing burn temperatures and controlling the amount of oxygen present can lessen nitrogen oxide emissions - however, lowering temperatures and oxygen supply can result in less complete combustion, reducing the efficiency of the process and increasing the amount of particulates and carbon monoxide - finding the exact mix of air, temperature, oxygen, and other factors is a significant challenge
Mobility of Acid Deposition
- acid deposition crosses international borders between the US and Canada and is carried from England, Germany, and the Netherlands to Scandinavia - due to this mobility, the precursors to acid deposition emitted in one region have a significant impact on another region/country - there have been legislative and legal attempts to restrict emissions from coal-burning power plants in the midwestern United States that fall as acid deposition in Canada - recently observed acid deposition documented along the West Coast of the United States is believed to be the result of coal combustion in China - sulfur and nitrogen oxides are released in China and elsewhere in Asia and are carried by the prevailing westerlies from one continent to another, across the Pacific Ocean - these pollutants reach the western United States, are deposited on the ground as rain and snow, and intercepted by vegetation in California, Oregon, and Washington State
Clean Air Act Effect
- all criteria air pollutants have decreased considerably in the United States over the last two decades - the decrease for lead is the greatest - only ozone and lead concentrations have been close to or above the NAAQS in the last few years
Acidity of Rain
- all rain is naturally somewhat acidic - the reaction between water and atmospheric carbon dioxide lowers the pH of precipitation from neutral 7.0 to 5.6
Consequences to Pollution Control
- all three types of pollution control devices use additional energy and increase resistance to airflow in the factory or power plant - therefore, they require the use of more fuel and result in increased carbon dioxide emissions
Challenges Controlling Photochemical Smog and Ozone
- although sulfur, nitrogen, and carbon monoxide pollution have been reduced below the standards of the Clean Air Act, the American Lung Association reported in 2017 that over 125 million people within the United States were exposed to air that did not comply with the maximum allowable ozone concentration - the chemistry of smog formation and the behavior of the atmosphere during changing weather conditions make smog formation very complex, difficult to predict, and difficult to reduce
The Buildup of Photochemical Smog: Abundant Ozone Accumulation and Inadequate Ozone Destruction
- anthropogenic VOCs: spilling gasoline on pavement - natural VOCs: forests - in a small supply, VOCs form very little amounts of photochemical smog during the natural cycle of ozone formation and destruction that takes place daily - however, when VOCs are present in larger quantities: 1. sunlight causes nitrogen dioxide to break apart into NO + O 2. the free oxygen atom combines with O2 to form ozone (O3) 3. however, because VOCs have combined with nitrogen oxide in a strong bond, NO isn't available to combine with ozone 4. since NO isn't available to break down ozone by recombining with it, a larger amount of ozone accumulates 5. contributing to the daytime accumulation of ozone in urban areas with an abundance of both VOCs and nitrogen dioxide 6. trees and shrubs in rural areas produce VOCs that can contribute to the formation of photochemical smog, as do forest fires that begin naturally
Wet Scrubber
- attacks particulate matter and sulfur dioxide - particles are "scrubbed" from the exhaust stream by water droplets and the water-particle "sludge" is collected and processed for disposal - uses a combination of water and air that separates and removes particles - particles are removed in the scrubber in a liquid or sludge form and clean gas exits - particles are sometimes ionized before entering the scrubber to increase its efficiency (similar to electrostatic precipitators) - scrubbers also remove sulfur dioxide - ground limestone added to the water (slurry) reduces sulfur dioxide
Effects of Particulate Matter
- can exacerbate respiratory and cardiovascular disease and reduce lung function - may lead to premature death - particulate matter from air pollution scatters light and contributes to haze/smog, reducing visibility - at high concentrations (after a large forest fire or volcanic eruption), incoming solar radiation in the region can be reduced enough to affect photosynthesis
Carbon Oxides
- carbon monoxide (CO) is a colorless, odorless gas that is formed during incomplete combustion of most matter - a common pollutant in vehicle exhaust and most other combustion processes - produced by malfunctioning exhaust systems or natural gas heaters, and poorly ventilated cooking fires (lacking enough oxygen) - carbon monoxide can be a significant component of air pollution in urban areas - a particular problem in developing countries, where people may cook with manure, charcoal, or kerosene within poorly ventilated structures
Catalytic Converter
- catalyst: increases the speed of a reaction, can be re-used again and again - unburnt fuel residue, nitrous oxides, and carbon monoxide enter the converter as toxic gases - water vapor, oxygen, nitrogen, carbon dioxide exit (harmless substances) - movement of toxic gases through the converter: HC, CO, NOx --> N2, H2O, CO2 - micro ducts are coated with precious metals (mostly platinum and palladium) that cause toxic gases to react and re-combine to produce harmless gases - transformation happens most efficiently when the converter is hot (the toxic gases and the chemical reactions provide heat) - can eliminate 99% of the motor's toxic gasses at ideal temperature - emits 5x less pollution
Anthropogenic Contributions to Ozone Destruction
- certain chemicals can break down ozone, particularly chlorine - the major source of chlorine in the stratosphere are compounds known as chlorofluorocarbons (CFCs) - CFCs have been used in refrigeration and air conditioning, as propellants in aerosol cans, and as "blowing agents" to inject air into foam products, like Styrofoam
Some of the Most Polluted Cities in the World
- cities in China and India - Zabol, Iran
Air Pollution Outputs
- components of the atmosphere and biosphere that remove air pollutants - air pollution can be removed or altered by vegetation, soil, and components of the atmosphere such as clouds, particles, or gases
Direct v.s. Indirect Effects of Acid Deposition
- direct: a decrease in the pH of lake water - indirect: the mobilization of metals - often difficult to determine whether an effect is direct or indirect, making remediation challenging
Sulfurous (Gray) Smog
- dominated by sulfur dioxide and sulfate compounds - also called London-type smog, gray smog, or industrial smog - found in areas with a lot of coal burning (Victorian London) SOx (sulfur oxides) + PM (particulate matter) + fog = sulfurous smog
Carbon Dioxide
- not included among the criteria air pollutants in the 1970 CAA - today it is widely accepted that carbon dioxide (CO2) is altering ecosystems in a substantial way - it is a colorless, odorless gas formed during the complete combustion of most matter, including fossil fuels and biomass - CO2 is absorbed by plants during photosynthesis and is released during respiration - however, burning fossil fuels has contributed additional carbon dioxide to the atmosphere and led to its becoming a major pollutant - as a greenhouse gas, it contributes to global warming - CO2 recently exceeded a concentration of 400 parts per million in the atmosphere and appears to be steadily increasing each year - in 2007, the U.S. Supreme Court ruled that CO2 should be considered an air pollutant under the Clean Air Act - in 2012, a federal appeals court agreed that the EPA is required to impose limits on harmful greenhouse gas emissions, including CO2
Nitrogen Oxide (NO)
- one oxygen atom per nitrogen atom - a colorless, odorless gas - can easily transform to NO2 in the atmosphere
Photochemical oxidant
- oxides are reactive compounds that remove electrons from other substances - photochemical oxidants are a class of air pollutants formed by sunlight acting on chemical compounds such as nitrogen oxides and sulfur dioxide - many different photochemical oxidants - generally harmful to plant tissue, human respiratory tissue, and construction materials - also cause economic harm, since poor visibility in popular vacation destinations can reduce tourism revenues for recreation areas (lower incomes for hotels and restaurants in these areas)
Breakdown of Ozone
- ozone is broken down into O2 and free oxygen atoms when it absorbs UV-B or UV-C ultraviolet light: O3 + UV-B or UV-C ---> O2 + O
Forest fires release
- particulate matter - nitrogen oxides - carbon monoxide
Secondary pollutants
- pollutants that have undergone transformation in the presence of sunlight, water, oxygen, or other compounds - because solar radiation provides energy for many of these transformations, and because water is usually involved, the conversion to secondary pollutants occurs more rapidly during the day and in wet environments - includes ozone (O3), sulfate (SO42-), and nitrate (NO3-) - when trying to control secondary pollutants, it is necessary to consider the primary pollutants that create them, as well as factors that may lead to the formation, breakdown, or reduction of the secondary pollutants - example: when municipalities try to reduce ozone concentrations in the air, they focus on reducing the compounds that lead to ozone formation (NOx & VOCs) rather than on the ozone itself
Primary pollutants
- polluting compounds that come directly out of the smokestack, exhaust pipe, or natural emission source - include CO, CO2, SO2, NOx, and particulate matter (PM) - also includes many VOCs, most hydrocarbons, and most suspended particles - as gasoline is burned in a car, it volatilizes from a liquid to a vapor, some of which is emitted from the exhaust pipe in an uncombusted form (the effect is more pronounced if the car is not operating efficiently)
Mobile Sources (transportation)
- primarily vehicles - the largest sources of carbon monoxide and nitrogen oxides
Electrostatic precipitators
- remove particulate matter by using an electrical charge to make particles coalesce - polluted air enters the precipitator and the electrically charged particles within are attracted to negative or positive charges on the sides of the precipitator - the particles collect and relatively clean gas exits the precipitator - does not reduce gas
Control of Particulate Matter
- removing PM is the most common means of pollution control - the process of removing PM may also remove sulfur - the simplest method used is gravitational settling: relies on gravity as the exhaust travels through the smokestack - the particles settle out to the bottom and the ash residue that accumulates can be disposed of in a landfill - depending on the fuel that was burned, the ash may contain sufficiently high concentrations of metals that require special disposal
Nitrogen Oxides (NOx) Effects
- respiratory irritant - increases susceptibility to respiratory infection (really young people, old people, and asthmatics, are most susceptible) - an ozone precursor, leads to the formation of ozone and photochemical smog (nitrogen oxides are an ingredient in ozone gas) - converts to nitric acid in the atmosphere, which is harmful to aquatic life and some vegetation (acid rain, acid deposition) - contributes to over-fertilizing terrestrial and aquatic systems
Photochemical (Brown) Smog
- smog that is dominated by oxidants such as ozone - also known as Los Angeles-type smog or brown smog - found in areas with a lot of cars and sunlight - Los Angeles - New York - Sydney NOx (nitrogen oxides) + VOCs (volatile organic compounds, gasoline) + sunlight = photochemical smog
Smog
- smoke + fog + sulfur dioxide - a mixture of oxidants and particulate matter - when photochemical oxidants are in the presence of sulfur and nitrogen oxides, they can enhance the formation of certain PM and contribute to scattering light, resulting in smog - smog is partly responsible for the hazy view and reduced sunlight observed in many cities - it can be divided into two categories: 1. photochemical smog 2. sulfurous smog
Volcanoes release
- sulfur dioxide - particulate matter - carbon monoxide - nitrogen oxides
Across the globe natural air pollutant emissions
- sulfur dioxide emissions: 30% natural - nitrogen oxide emissions: 44% natural - VOC emissions: 89% natural **however in North America the anthropogenic contribution is much greater (could be as much as 95% for NOx and SO2)
Chlorofluorocarbons (CFCs)
- synthetic human-made chemical - non-flammable, non-toxic, does not react with anything - created to prevent toxic gases leaked by refrigerators and air conditioning units - hairspray, spray paint, and other aerosol cans release CFS - the chlorine in CFCs acts as an assassin of ozone - when CFCs are released into the troposphere they eventually make their way to the stratosphere because they are unreactive - under cold conditions, ultraviolet radiation has enough energy to break the bond connecting chlorine to the CFC molecule - the chlorine atoms are then able to break apart ozone molecules CFC + UV radiation --> one free chlorine atom
Mercury's Current and Future Status
- the EPA regulates mercury through its Hazardous Air Pollutants program - as a result of the release of mercury into the air, primarily from the combustion of fossil fuels (especially coal), the concentrations of mercury in both air and water have increased dramatically in recent years - emissions standards for coal plants will likely be the focus of future regulations
Movement of Pollutants
- the atmosphere is one of the major repositories for air pollutants (a place where things are or may be stored) - in recent years, air pollution in Asia has been responsible for acidic rainfall on the West Coast of the United States - particulates and sulfate aerosols are most responsible for causing pollution and reducing visibility in cities - pollution can also be transported long distances and cause problems far from the source
Atmospheric Brown Cloud
- the combination of particulate matter and ozone - derived primarily from combustion of fossil fuels and burning biomass - have been observed in cities and throughout entire regions, especially in Asia - their brownish tint is typically caused by the presence of black or brown light-absorbing carbon particles and/or nitrogen dioxide
Controling pollutants after combustion
1. Automobiles (mobile sources): - Catalytic converters 2. Power plants and factories (stationary sources): - Fluidized bed combustion - Scrubbers - Baghouse filters - Electrostatic precipitators
How does atmospheric temperature influence the formation of smog?
1. VOC emissions from trees/vegetation and evaporation of volatile liquids (gasoline), increase as the temperature increases 2. NOx emissions from fuel combustion by electric utilities are also greater with high air-conditioning demands in hot weather 3. chemical reactions that form ozone and other photochemical oxidants proceed more rapidly at high temperatures - these factors increase smog concentration when temperatures are higher
The scrubber process
1. dirty air enters scrubber 2. combustion exhaust stream moves upward in a shower of water mist 3. mist collects PM "scrubs the air" and brings them down to the bottom of the unit 4. dirty water moves to a sludge removal system 5. sludge is separated from water and disposed of 6. water moves back to the scrubber for reuse 7. excess mist collects on the screen 8. cleaner air exits through the stack
Fabric filters/Baghouse filters
1. dirty air enters the housing 2. The combustion exhaust stream moves through and dust particles are trapped in a series of filter bags 3. cleaner, filtered air moves out of unit 4. a shaker mechanisms is activated periodically to dislodge trapped particles, which can then be collected from beneath the unit - a type of filtration device that allows gases to pass through them but removes PM, does not reduce gas - often called baghouse filters - certain fabric filters can remove almost 100% of the PM emissions
Electrostatic Precipitator Process
1. dirty air enters the precipitator unit 2. particles in the combustion exhaust stream pass by negatively charged plates, which gives them a negative charge 3. the negatively charged particles are attracted to positively charged collection plates 4. cleaner air moves out of the unit 5. the positive collection plates are periodically discharged, which causes the particles to fall off so that they can be removed from the system
Anthropogenic Sources of Particulate Matter
1. fires 2. agriculture 3. dust 4. power plants 5. mobile 6. miscellaneous 7. industrial processes
Break Down of CFC Ozone Destruction
1. first, chlorine breaks ozone's bonds and pulls off one atom of oxygen, forming a chlorine monoxide molecule and O2: O3 + Cl ---> ClO + O2 2. next, a free oxygen atom pulls the oxygen atom from ClO, liberating the chlorine and creating one oxygen molecule: ClO + O ---> Cl + O2 **Chlorine acts as a catalyst because it starts and ends up as a free Cl atom, whereas an ozone molecule and a free oxygen atom are converted into two oxygen molecules (lost) one chlorine atom can catalyze the breakdown of as many as 100,000 ozone molecules before it leaves the stratosphere
Anthropogenic Sources of Carbon Monoxide
1. mobile 2. fires 3. biogenics 4. fuel combustion 5. miscellaneous 6. industrial processes
Anthropogenic Sources of Nitrogen Oxides
1. mobile 2. power plants 3. industrial processes 4. biogenics 5. fires 6. miscellaneous
Anthropogenic Sources of Sulfur Dioxide
1. power plants 2. industrial processes 3. fires 4. mobil 5. miscellaneous
Acid Deposition Diagram
1. primary pollutants such as sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere 2. oxidants are taken with the wind 3. secondary pollutants are created by the combination of primary pollutants and sunlight/water in the atmosphere 4. sulfuric acid and nitric acid made in the clouds rain down as acid precipitation
Percent Change in U.S. Air Quality
Carbon monoxide (CO) -87% Ozone (O3) -29% Lead (Pb) -98% Nitrogen Oxides (NOx) -67% PM10 -46% Sulfur Dioxide (SOx) -94%
Other Pollution Control Measures
Municipalities have tried a number of strategies: - Reduce gasoline spilled at the pump, restrict evaporation of dry-cleaning fluids, and the use of lighter fluid - Reduce the use of wood-burning stoves and fireplaces (prevents emissions of nitrogen oxide, PM, VOCs, and carbon monoxide) - Limit automobiles to every other day use or charge user fees for roads during heavy commute times (plans permitting automobiles to be driven only every other day) In China, during the 2008 Beijing Olympics, the government successfully expanded public transportation networks, imposed motor vehicle restrictions, and temporarily shut down many industries as a way to reduce photochemical smog and improve visibility Successful as a short-term air pollution control measure
Natural Ozone Accumulation (day)
NO2-> NO + O-> O + O2-> O3 1. occurs during the day in the presence of sunlight 2. when an abundance of nitrogen oxides is present in the atmosphere (from natural and anthropogenic sources), with few VOCs present, nitrogen dioxide (NO2) splits to form nitrogen oxide (NO) and a free oxygen atom (O) 3. in the presence of energy inputs from sunlight, this free oxygen atom combines with diatomic oxygen (O2) to form ozone (O3) 4. with abundant nitrogen dioxide and abundant sunlight, ozone accumulates in the atmosphere
Natural Ozone Destruction (after sunset)
O3 + NO -> O2 +NO2 1. when sunlight intensity decreases and nitrogen oxide is still present in the atmosphere, the ozone combines with nitrogen oxide (NO) and re-forms into O2 + NO2 2. this is a natural process that happens in the latter part of the day and evening
UV Radiation
UV-A: Not absorbed by the ozone layer UV-B: Mostly absorbed by the ozone layer, but some does reach the Earth's surface UV-C: Completely absorbed by the ozone layer and atmosphere (O2)
Lightening strikes create
nitrogen oxides from atmospheric nitrogen
What is the Polar Vortex
sometimes during the winter, the jet stream dips southward, sending cold Arctic air into the United States
Great Salt Lake (1985 vs. 2022)
the water level of the lake has significantly decreased, exposing the lake bed to the atmosphere and increasing particular matter (dust containing heavy metals) in the air
Mercury (Hg)
- not a criteria air pollutant human-derived sources: -coal - oil - gold mining - coal-fired electricity generation plants remain the largest uncontrolled source of mercury effects/impacts: - impairs the central nervous system - bioaccumulates in the food chain
Seasonal Ozone "Hole" Depletion in Antarctica
- each year the depletion occurs from roughly August through November 1. extremely cold weather conditions during the polar winter, our summer (June, July, August) cause a buildup of ice crystals mixed with nitrogen oxide (below -78 degrees C) 2. this in turn provides the perfect surface for the formation of the stable molecule Cl2, which accumulates as atmospheric chlorine interacts with the ice crystals 3. when the Sun reappears in the spring, UV radiation breaks down this molecule into Cl again, which in turn catalyzes the destruction of ozone - mid-spring at poles (September, October) is the lowest O3 concentration point - because almost no ozone forms in the dark of the polar winter, a large amount of thinning occurs - only after the temperatures warm up and the chlorine gets diluted by air coming from outside the polar region does the thinning diminish - by summer, ozone production is greater than depletion - ozone is still being destroyed it is just not concentrated in one single point of Antarctica
UV-B Exposure
- exposure to UV-B radiation increases the risk of skin cancer and cataracts - suppresses the immune system in humans - also harmful to the cells of plants, and it reduces their ability to convert sunlight into usable energy - UV-B exposure can therefore have adverse impact on ecosystem productivity and harm entire biological communities example: losses of phytoplankton—the microscopic algae that form the base of many marine food chains—will cause the depletion of fisheries
Formation of Ozone
- first, UV-C radiation breaks the bonds holding together the oxygen molecule O2, leaving two free oxygen atoms: O2 + UV-C ---> O + O - sometimes the free oxygen atoms react with oxygen molecules, resulting in ozone: O + O2 ---> O3
Developed Countries
- gas stoves and gas heaters are much cleaner than burning wood or biomass - particulate matter does not necessarily exist in dangerous forms in house of developed countries
Depletion of the Ozone Layer
- global ozone concentrations have decreased by more than 10% since the late 70s - depletion is greatest at the poles (especially Antarctica) - decreased stratospheric ozone has increased the amount of UV-B radiation that reaches the surface of Earth - an ozone hole exists above Antarctica
The ozone layer
- gravity keeps gases from escaping into the outer space, not the ozone layer - the ozone layer is just an area with a higher concentration of ozone in the stratosphere
Reducing Acid Deposition
- has been reduced in the US due to lower sulfur dioxide and nitrogen oxide emissions - this improvement is a result of the Clean Air Act Amendments that were passed in 1990 and implemented in 1990 and 1995
Smog Reduction
- historically, most local smog reduction measures have been directed primarily at reducing emissions of VOCs in urban areas - with fewer VOCs in the air there are fewer compounds to interact with nitrogen oxides, and thus more nitrogen oxide will be available to recombine with ozone - more recently, efforts to control ozone have focused on reducing nitrogen oxide emissions, which appears to be more effective at controlling smog in areas away from urban centers
Acid Deposition and Building Materials
- hydrogen ions in acid deposition interact with limestone or marble - the calcium carbonate reacts with H+ and gives off Ca2+ - in the process, the calcium carbonate material is partially dissolved - the more acidic the precipitation, the more hydrogen ions there are to interact with the calcium carbonate - gaseous sulfur dioxide (SO2) or sulfuric acid vapor, has also contributed to the deterioration - acid deposition erodes many exposed painted surfaces, including automobile finishes
Lead (Pb) Effects
- impairs central nervous system - can affect learning and intelligence, particularly for young children who are attracted by the sweet taste of lead-based paint and may ingest the dust or chips - at low concentrations, can have measurable effects on learning and the ability to concentrate - lead traces in your blood are associated with criminal violent activity
Black Triangle
- large areas in Germany, Poland, and the Czech Republic contain a great deal of "brown" coal or lignite that provides fuel for nearby coal-fired power plants and other industries - emissions from the combustion of this high-sulfur-content coal once caused this "Black Triangle" to become one of the most polluted areas in the world - in addition to human health problems such as respiratory illnesses, forest ecosystems in this region have also been damaged in the last 40 years
Acid Deposition
- largely the result of human activity, although natural processes (volcanoes), may contribute to its formation - occurs when nitrogen oxides (NO & NO2) and sulfur dioxide (SO2) are released into the atmosphere - these primary pollutants combine with atmospheric oxygen and water, forming the secondary pollutants nitric acid (HNO3) and sulfuric acid (H2SO4) - these compounds break down further, producing inorganic pollutants (nitrate & sulfate) as well as hydrogen ions (H+) that generate the acidity in acid deposition - pollutants may travel a thousand kilometers (600 miles) or more - eventually, the secondary pollutants are washed out of the air and deposited as precipitation or as gas on vegetation, soil, or water
Formulation of the Clean Air Act
- legislators used information from environmental scientists and human health scientists on the most important air pollutants to monitor and control - the original act identified 6 pollutants that significantly threaten human well-being, ecosystems, and structures - these were called criteria air pollutants because, under the Clean Air Act, the EPA must specify allowable concentrations of each pollutant
Sources of Air Pollution (Inputs)
- many pollutants are naturally and normally existing (volcanoes and fires) - can be anthropogenic (automobiles and factories) - inputs do not originate from just one location - inputs can come from automobiles on the ground, airplanes in the sky, or vegetation (tree leaves) 100 feet in the air
Volatile Organic Compounds (VOCs)
- not a criteria air pollutant - VOCs are organic compounds that evaporate at typical atmospheric temperatures - many VOCs are hydrocarbons (compounds that contain carbon-hydrogen bonds, such as gasoline, lighter fluid, dry-cleaning fluid, oil-based paints, and perfumes) - formed by evaporation of fuels, solvents, paints, and improper combustion of fuels such as gasoline - they are not necessarily hazardous - VOCs given off by conifer trees cause no direct harm - however, VOCs play an important role in the formation of photochemical oxidants such as ozone (precursor to ozone formation) - therefore, they have the potential to be harmful
Effects of Acid Deposition
- the greatest effects of acid deposition have been on aquatic ecosystems - lower pH of lakes and streams has caused decreased species diversity of aquatic organisms - many species can survive and reproduce only within a narrow range of environmental conditions (amphibians will have developmental and reproductive problems in a pH of 6.0 or 5.5) - in water below pH 5.0, most salamander species cannot survive - a lower pH can mobilize metals (aluminum & mercury), releasing organic and inorganic compounds from soils and sediments into surface water - exposure to metals can impair the physiological functioning of aquatic organisms, leading to species loss - decreased pH can also affect the food sources of aquatic organisms, creating indirect effects at several trophic levels - the red spruce at high elevations in the northeastern United States was shown to have been harmed by acid deposition (the acidity of deposition and by the nitrate and sulfate ions) - harm human-built structures such as statues, monuments, and buildings
Air Pollution
- the introduction of chemicals, particulate matter, or microorganisms into the atmosphere at concentrations high enough to harm plants, animals, and materials such as buildings, or to alter ecosystems - particulate matter: tiny things floating in the air, dust, ash - microorganisms: mold spores in the air - generally refers to pollution in the troposphere, the first 16 km (10 miles) of the atmosphere above the surface of Earth - can be called ground-level pollution
Why is the breakdown of ozone harmful
- the ozone molecules are no longer available to absorb incoming UV-B radiation - as a result, the UV-B radiation can reach Earth's surface and cause harm to biological organisms.
Nitrogen Dioxide (NO2)
- two oxygen atoms per nitrogen atom - a pungent, reddish-brown gas - can easily transform to NO in the atmosphere
Avoiding Emissions
- using fuels that contain fewer impurities (coal and oil occur naturally with different sulfur concentrations and are available for purchase at a variety of sulfur concentrations) - typically low-sulfur coal or oil is more expensive to purchase than coal or oil containing higher sulfur concentrations - however, wherever fuel is combusted, pollution will be emitted - therefore, most attempts to reduce air pollution will depend on the control of pollutants after combustion
Fluidized Bed Combustion Chamber
- way to reduce sulfur dioxide emissions from coal exhaust - exist at coal-burning power plants - sulfur oxides are why coal is dirty (they are harmful to breathe in and contribute to acid rain) - burning granulated coal in the presence of calcium carbonate (granulated limestone) - the heated calcium carbonate absorbs sulfur dioxide and produces calcium sulfate (a solid) - calcium sulfate can be used in the production of gypsum wallboard (sheetrock) for houses - some of the sulfur oxide that does escape the combustion process can be captured by other methods after combustion SO2 + CaCO3 --> CaSo3 + CO2
Thermal Inversion
- when a relatively warm layer of air at mid-altitude covers a layer of cold, dense air below - the warm inversion layer traps emissions that then accumulate beneath it - normally, temperature decreases as altitude increases, leaving the warmest air closest to Earth - this warm air, which is less dense than the colder air above it, can easily rise and disperse pollutants into the upper atmosphere (allowing pollutants from the surface to be reduced or diluted by all of the atmosphere above) - however thermal inversion can occur which traps a warm layer of air between two cooler layers - the lower cool layer (closest to Earth's surface) is denser than the air above it, preventing pollutants from rising - trapped emissions in the inversion layer can cause a severe pollution event in cities with high concentrations of vehicle exhaust and industrial emissions
