The degree to which a toxic air pollutant affects a person's health depends on many factors, including the quantity of pollutant the person is exposed to, the duration and frequency of exposures, the toxicity of the chemical, and the person's state of health and susceptibility.
Scientists estimate that millions of tons of toxic pollutants are released into the air each year.
Some air toxics are released from natural sources such as volcanic eruptions and forest fires. In addition, many routine activities around the home, such as using gas-powered lawnmowers and tools, or using volatile paints and cleaning solvents, release toxic pollutants into the air. The list of toxic air pollutants in the Clean Air Act is a long one, and it includes some familiar names, such as benzene. Benzene is a known cancer-causing substance that is a component of gasoline and some cleaning solvents. Gasoline sold in the United States is, on average, 1.6 percent benzene.