Smaller particulates, which float in the air, can be inhaled deeply and, with elevated concentrations over an extended period of time, can cause lung damage and bronchitis. Recent studies have linked exposure to these smallest particles to a greater risk of premature death. At present, automobiles are the main source of nitrogen oxide emissions in urban areas. Nitrogen oxides, at elevated concentrations, can damage the respiratory system. They also can be a key ingredient in the formation of both ozone and acid rain.
Sulfur dioxide is released when sulfur-containing fuels like coal and oil are burned.
Common sources of sulfur dioxide emissions are electric utilities and certain industrial processes. Sulfur dioxide at elevated concentrations can cause respiratory problems. It also can be a contributing component of acid rain. Toxic chemicals such as benzene, toluene and 1,1,1 trichloroethane , when present in the air that we breathe in elevated concentrations over time, can cause various health effects including birth defects, cancer and other health problems. Sources of toxic emissions include industrial processes, such as refineries and chemical manufacturers, small businesses such as printers and dry cleaners and automobiles.