Particulates of both natural and human origin also cause pollution. Smoke both natural from fires and human activities cause from industries and other sources are major and cause much damage . The chemicals that are most trouble-some in air pollution are formed in the atmosphere by gases.
The pollutant introduced into the atmosphere in the largest quantities by human activity is carbon monoxide. It is the product of incomplete combustion and the largest contribution comes from exhaust. Carbon monoxide is a colorless, odorless, tasteless gas, with the formula CO.
Carbon dioxide (CO2) is also a product of combustion of fossil fuels. It is a minor constituent of natural air (about 0.03%), but the increased use of fossil fuels may cause an increase in the amount of carbon dioxide in the atmosphere.
The gases given off by engine exhaust are the oxides of nitrogen and the unburned hydrocarbons. The energy that causes these gases to react to form new compounds, comes from the sun. This reaction is called a photochemical reaction. The “air” that is exhausted from diesel engines is also too poor to breathe, although it contains more oxygen per cubic foot, but more particles.
Ozone is a chemically reactive substance (03) that is sometimes used to deodorizing exhausts by oxiding them to less objectionable odorous products before they are released to the atmosphere.
Industrial or gray smog is considered the most serious type of air pollution. Smoke and oxides of that are released by burning coal and oil containing minor amounts of sulfur is the cause.
The oxides of sulfur form sulfuric acid in the atmosphere which is both toxic to life and damaging to many materials. The smoke gives the air a gray color.
Industrial smog has been known to cause air pollution disasters. One of the worst occurred in London in December of 1952. Five days of stagnant air brought about high pressure systems caused between 3,500 and 4,000 deaths. In Donora, Pennsylvania 20 died and 6,000 became ill in 1948 because of a similar instance.
Photochemical smog also know as brown smog is largely caused by exhaust gases. It is common in warm cities in dry areas with lots of sunshine, such as Los Angeles, Denver, and Salt Lake City. This type of smog can obscure vision, cause plant damage, and irritate eyes.