Air pollutants from a variety of natural and industrial sources and human activity can contaminate the air we breathe. In 1990, Congress amended the Clean Air Act to include regulatory programs that would control hazardous air pollutant emissions. Hazardous air pollutants, or HAPs, are chemicals suspected of causing cancer or other serious health conditions or adverse environmental impacts. Such pollutants are also commonly called "air toxics" or "toxic air pollutants". Air toxics in the air and the numbers of people breathing them contribute to the health hazard and risk.
Air toxics can take the form of particulate matter or vapor. Toxic air pollutants can be chemically classified as volatile (quickly evaporates at room temperature and pressure) or semi-volatile (evaporates less readily). Particulate matter includes metals such as chromium, cadmium and mercury. Volatile air toxics include chemicals such as benzene, toluene, xylene, and methylene chloride. Dibenzofuran, naphthalene and phenol are examples of semi-volatile chemicals.
In 1990, North Carolina established regulations for the control of toxic air pollutants (TAPs) to help protect the health of its citizens. The North Carolina Air Toxics program is a health-based regulatory program that establishes acceptable ambient levels (AALs) to limit emissions of air toxics. North Carolina's strategy for controlling air toxics emissions consists of air permitting and compliance activities, measuring ambient levels of toxic air pollutants, directing and implementing an air quality chemical accident prevention program, and conducting chemical risk assessments. The federal program manages emissions by requiring the use of specific equipment and work practices. The federal and state programs work together to control and minimize toxic air pollutant emissions.