Coarse particles generally remain in the form in which they are released into the atmosphere without chemical transformation, eventually settling out under the influence of gravity. When inhaled, they tend to be deposited in the upper parts of the respiratory system from which they can be eventually expelled back into the throat. These precursors result from combustion sources, solvent use and agricultural activities. Combustion sources include vehicle exhaust, electrical power plants, industrial boilers, residential heating, wood burning stoves and some industrial processes. Solvents are used in many products and by industries such as printing and auto re-finishing.
Ammonia results primarily from agricultural operations.
The effect is even more acute with smaller PM 2.5 particles. Health effects include breathing and respiratory symptoms, irritation, inflammation and damage to the lungs, and premature death. Particulate matter is not limited to urban areas. PM is also an effective delivery mechanism for other toxic air pollutants, which attach themselves to particulate matter that floats in the air. These toxics are then delivered into the lungs, where they can be absorbed into the blood and tissue.