In high doses, smog can harm humans by causing breathing difficulty for asthmatics, coughs in children, and general illness of the respiratory system. Acid rain can harm vegetation and run into lakes and rivers which changes the chemistry of the water, and makes it potentially uninhabitable for all but acid-tolerant bacteria. Nitrogen oxides are produced from burning fuels, including gasoline and coal. Particulate Matter is any type of solid in the air in the form of smoke, dust, and vapors, which can remain suspended for extended periods. Aside from reducing visibility and soiling clothing, microscopic particles in the air can be breathed into lung tissue becoming lodged and causing increased respiratory disease and lung damage.
Particulates are also the main source of haze, which reduces visibility.
Particulates are produced by many sources, including burning of diesel fuels by trucks and buses, fossil fuels, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining, agricultural burning, and operation of fireplaces and woodstoves. SO 2 is a gas produced by burning coal, most notably in power plants. Some industrial processes, such as production of paper and smelting of metals, produce sulfur dioxide. Like nitrogen oxides, SO 2 is a major contributor to smog and acid rain. SO 2 is closely related to sulfuric acid, a strong acid.