The term area source is used to describe the many smaller stationary sources located together whose individual emissions may be low but whose collective emissions can be significant. Typically area sources are those that emit less than 25 tons per year of any combination of hazardous air pollutants, or less than 10 tons per year of any single hazardous air pollutant. A mobile source of air pollution refers to a source that is capable of moving under its own power. In general, mobile sources imply on-road transportation. Agricultural Sources Agricultural operations, those that raise animals and grow crops, can generate emissions of gases, particulate matter, and chemical compounds.
Manure emits various gases, particularly ammonia into the air.
This ammonia can be emitted from the animal houses, manure storage areas, or from the land after the manure is applied. In crop production, the misapplication of fertilizers, herbicides, and pesticides can potentially result in aerial drift of these materials. Natural Sources Natural sources of air pollution are sources not caused by people or their activities. Air transport is the term used to describe the mechanism by which air pollution moves from an emissions source to a receptor. The wind is the transporter of pollutants from sources and receptors.