Major and Area Sources of Emissions
The regulations and controls on stationary sources in the United States have generally been designed to focus on two types of stationary sources:
Major stationary sources whose emissions exceed a nominal threshold defined in the CAA or by a regulatory agency.
Area sources whose emissions fall below the threshold.
Major stationary sources (such as factories and electricity-generating facilities) are defined as single sources with emissions exceeding a threshold level that depends on the pollutant. This threshold is generally 100 tons/yr for criteria pollutants and their precursors; however, the threshold for Pb is 5 tons/yr. For the most severe O3 nonattainment areas, the threshold for VOC can be as low as 10 tons/ yr. For serious CO nonattainment areas, the CO threshold is 50 tons/yr. The reporting requirements for major stationary sources are more detailed than those for area sources (65 Fed. Reg. 33268 ).
One important distinction between major stationary and area sources is the method used to estimate and control their emissions. Major stationary sources are inventoried individually and their emissions are generally controlled through a permitting process that requires specific regulatory review of each individual facility. Area sources, which are generally widely dispersed sources arising from relatively small industrial and business facilities (for example, agricultural fields and small copying and printing shops) or from application and use of consumer products (for example, architectural coatings), are inventoried and regulated collectively.