Transportation accounts for nearly half the air pollution in the U.S.
Another large source is from the combustion of oil and coal to produce electricity.
Sources of natural pollution:
1) volcanic eruptions
2) forest fires
3) dust storms
4) vegetation
5) salt particles from ocean waves
6) hot springs
Sources of industrial air pollution:
1) paper mills
2) power plants
3) refineries
4) manufacturing
Air pollutant types:
1) Sulfur dioxide (SO2)- colorless gas that comes mostly from burning coal and oil in
power plants, petroleum refineries and paper mills. Can lead to formation of acid rain.
2) Carbon monoxide(CO)- poisonous gas produced by the incomplete burning of carbons
in fuels. Comes mostly from transportation.
3) Nitrogen Oxides- come from high temperature combustion of fuel. Comes mostly from
power plants and motor vehicles.
Luckily, since the Clean Air Act became law in 1970, total air pollution has been reduced
35% in the U.S.
Fossil fuel burning, which leads to greenhouse effect, also release nitrogen oxide, CO, and
lead.
Smog forms from ozone at ground level. It combines with other pollutants producing
harmful smog.
Smog contains substances that damage vegetation and can irritate the eyes and lungs.
Thermal Inversion- occurs when air near the ground is cooler than the air higher in the
atmosphere. This results in a buildup of pollutants and usually happen when winds are 8
km/hr or less.
How a Thermal Inversion Traps Pollutants Near the Surface:
1) at night or in winter, coldest air may be at the surface with warmer air above it
2) cold air sinks keeping the pollutants trapped, unable to rise up.
Formation of Acid Precipitation:
1) pollutants such as nitrogen dioxide(NO2)and sulfur dioxide (SO2) are released from
industry or transportation.
2) they go into the atmosphere and react with hydrogen and form sulfuric acid (H2SO4)
and nitric acid(HNO3)
3) water vapor in rising air condenses on particles of H2SO4 and HNO3.
4) once water vapor pollutants as condensation nuclei it forms acid rain.
Lichens are natural monitors of air pollution.
The higher the level of sulfur dioxide in the air, the more the growth of lichen decreases.