Because the air we breathe comes to us through the earth's atmosphere, it naturally contains moisture and solid particulates. These enter the atmosphere as a result of natural processes such as evaporation from lakes and streams, volcanic eruptions, lightning strikes, forest fires, dust storms, sea spray and release of pollen. Man-made pollutants are of great concern to many people and organizations, including the National Park Service. The NPS is concerned about the following air pollutants which are linked to effects on park resources. These pollutants, their sources, and their effects are described below.
Sulfur dioxide is one of the most significant pollutants in the atmosphere.
Sulfur dioxide is very corrosive to stone, paint, and metals. Sulfur dioxide also aggravates existing respiratory diseases and contributes to the development of these conditions in humans. Plant species sensitive to atmospheric S02 include Douglas fir, ponderosa pine, white pine, and forest shrubs. Various crops are also affected, including alfalfa,.grains, squash, cotton, grapes, and apples. Sulfur dioxide ultimately transforms in the atmosphere into sulfates which are very fine particles measuring less than 2.5 millionths of a meter in diameter.