Particulates are trapped and filtered by leaves, stems and twigs, and washed to the ground by rainfall. They also weaken trees making them more susceptible to other health problems such as insects and diseases. Decay and burning of tropical forests. Aluminum and phospate fertilizer production, oil refineries, and steel manufacturing. Chemical reactions of sunlight on automobile exhaust gases.
Ozone is a major pollutant in smog.
The burning of fossil fuels for energy and large scale forest fires such as in the tropics are major contributors to the buildup of CO 2 in the atmosphere. Managing and protecting forests and planting new trees reduces CO 2 levels by storing carbon in their roots and trunk and releasing oxygen into the atmosphere.