Lecture 18: Air Pollution and Acid Rain
Chlorofluorocarbons?
(CFCs) Commonly called freons: Many types & many uses: refrigerants, AC, spray propellant, Styrofoam. -Act as greenhouse gases -affect climate. -Destroy stratospheric ozone -increases surface exposure to UV radiation. -Not natural sources. Some very long live in atmosphere, emissions regulated by international treaty. -Montreal protocol.
Nitrogen Oxides?
(NO & NO2) Major source is auto exhaust. Primary and secondary effects include acidification of lakes, respiratory irritation, leads to smog and ozone. Reduced using catalytic converters. -Gases air pollution.
Clean Air Act?
1970- mended 1977 and 1990. -Sets maximum emission levels for 7 different pollutants. -O2, NOx, CO, VOCs, O3, particulates, lead. -Monitored and enforced by EPA. -Some states (CA) have higher air quality standards than federal government.
Volatile Organic Compounds?
Abbreviated VOCs; compounds that contain carbon (organic) and evaporate very easily (volatile). -Gaseous compounds of hydrogen & carbon. -Benzene, vinyl chloride, isoprene, etc. -Involved in reactions that produce ozone & photochemical smog. *Sources: Industry (dry cleaning, degreasing, adhesives. -Combustion: car exhaust. -Natural sources: trees.
Photochemical Smog?
An atmospheric condition formed through a combination of weather conditions and pollution, especially from motor vehicle emissions. -Mix of primary pollutants: NOx, VOCs. -React with sunlight/oxygen to produce ground level ozone. -Formation dependent on weather conditions: Sunlight-Summer: limited mixing-inversion. -Smoggiest days: high pressure (subsidence inversion) in summer.
Primary Pollutants?
Chemical that has been added directly to the air by natural events or human activities and occurs in a harmful concentration -Emitted directly to air: SO2, NOx, CO, VOCs, Black carbon.
Carbon Monoxide?
Colorless, odorless, and poisonous gas. (CO). -Produced by incomplete combustion of fossil fuels: Not enough oxygen available during combustion. -Toxic event at very low concentrations: binds to hemoglobin-prevents it form carrying oxygen.
Stratospheric Ozone?
Good ozone, produces oxygen molecules to interact with UV radiation and prevent 95% of it from reaching the surface -
Ground Level Ozone?
Gunlight, oxygen and nitrogen react to produce ozone, can be harmful.
Sulfuric Acid?
H2SO4 (Strong Acid)
Nitric Acid?
HNO3 (Strong Acid)
What are the major pollutant types involved in photochemical smog and where do they come from? Why is photochemical smog a bigger problem in summer months?
Mix of primary pollutants-NOx, VOCs: reacts with sunlight/oxygen to produce ground level ozone. -Sources: car exhaus (NOx), industry & vegetation (VOCS). -Smoggiest days:A high pressure (subsidence inversion) in summer.
Why is rainwater naturally acidic? Explain the formation of acid rain and how it is different from naturally acidic rain?
Natural rain mildly acidic (pH 5.6) because CO2 in atmosphere dissolves in reainwater to form carbonic acid. -Sulfuric & nitric acids washed from atmosphere in rain. Fossil fuel use. Form sulfuric & nitric acids by reacting with oxygen & water. Form: By reaction of SO2 & NOx with water. Acid rain has pH ~4.5 -11x more acidic than normal rain.
Stationary Sources?
Non-moving sources of pollution, such as factories. -Mostly from coal power plants, industry. -Main source of SO2
Identify the major types of air pollutants, their major sources, and classify each as a primary or secondary pollutant?
Primary Pollutants-Gases: Sulfur Dioxide (SO2). Nitrogen Oxides NO & NO2 (NOx). Carbon monoxide (CO). Ozone (O3). Volatile organic compounds (VOCs). Secondary Pollutants-Particles: Combustion: black carbon (soot), gas to particle conversions (SO2 to sulfate, NOX to nitrate)
Secondary Pollutants?
Produced in atmosphere by: reactions between primary pollutants. -Sulfate, nitrate, ozone.
Acid Rain?
Rain that is more acidic (lower pH) than normal precipitation. -Sulfuric & nitric acids washed from atmosphere in rain. -NOx & SO2 from fossil fuel use. *Trees killed by acid rain & acid fog in smoky Mountains, TN.
Particulate Matter?
Solid particles or liquid droplets <10 microns in diameter. -Primary-emitted directly to atmosphere -black carbon. -Secondary: SO2 & NOx oxidized to particulate sulfate (SO4^2-) & nitrate (NO3-) **Important because: 1. Act as condensation nuclei for water vapor. 2. Reduce visibility. 3. Block or reflect solar radiation-Affect climate. 4. Human health risk. (Rural)
Mobile Sources?
Sources of air pollutants that move from place to place, example: automobiles, trucks, buses, and trains. -NO & NO2 from fossil fuel use.
How do temperature inversions form and why do they affect concentrations of airborne pollutants?
Temperature increases with height. Cooler, denser air near surface; warmer, lighter air above. Traps pollutants near ground increasing concentrations. -Occur: Common at night, surface heated during day-atmosphere warms from surface, up & mixes well. -Cool air settles at night, creates inversion & limits mixing. -When sun rises inversion breaks down as surface warms: inversion stronger & last longer during winter: longer nights, shorter days, & lower sun angle.
Inversion?
Temperature increases with height: Cooler, dense air near surface; warmer, lighter air above. Limits vertical mixing. Traps pollutants near ground increasing concentrations.
Sulfure Dioxide?
naturally from sea-spray and ocean vents; burning of coal and oil; acid rain -SO2 (Gas air pollution) -
