Smog is often worse away from the source of the smog-forming chemicals, since the chemical reactions that result in smog occur in the sky while the reacting chemicals are being blown away from their sources by winds. VOCs -Volatile Organic Compounds. Many of the organic chemicals we use do not occur in Nature, but were synthesized by chemists in laboratories. Examples include trees and vegetation, and microbial activity. Combustion - Burning.
Particulate pollution can cause eye, nose and throat irritation and other health problems.
2.5 - Fine particulate matter less than 2.5 micrometers in diameter that result from fuel combustion from motor vehicles, power generation, and industrial facilities, as well as from residential fireplaces and wood stoves. 10 - Coarse particulate matter less than 10 micrometers in diameter that are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations, as well as windblown dust.