This makes it difficult to predict changes in ozone levels accurately due to reductions in VOCs and NO 2 . VOCs evaporate into the atmosphere from motor vehicles, chemical plants, refineries, factories, consumer and commercial products such as lighter fluid, perfume, and other industrial sources. VOCs also occur naturally as a result of photosynthesis. Therefore, it concludes that current ozone reduction strategies may be misguided because they do not account for naturally occurring VOCs. Particulate Matter Particulate matter is the general term for a mixture of solid particles, including pieces of dust, soot, dirt, ash, smoke, and liquid droplets or vapor directly emitted into the air, where they are suspended for long periods of time.
Particulates can affect breathing, damage paints, and reduce visibility.
These particles derive from stationary, mobile, and natural sources. Environmental factors such as temperature inversion, wind speed, and wind concentration also affect SO 2 levels. Notes 1 National Report on Human Exposure to Environmental Chemicals , Centers for Disease Control, March 2001.