Basic Concepts

Early estimates of source contributions to particulate pollution were based on emission inventories that is, compilations of mass rates of discharge of particulate matter from various sources. Such inventories by themselves are of limited value in determining quantitatively contributions to the aerosol concentration at a given point, such as an air monitoring station. Emission inventories make no provision for natural background, or particle deposition between the source and the point of measurement. They also do not account for products of gas-to-particle conversion, which contribute significantly to the total mass of aerosols and affect visibility and health. An alternative approach, receptor modeling, makes use of chemical composition measurements at a sampling ("receptor") site in conjunction with information on the chemical signatures of sources to estimate source contributions. A major advantage of receptor modeling is that it requires no information on the wind field. The first receptor model to be developed, the chemical mass balance method (Hidy and Friedlander. 1971; Friedlander, 1973), is widely used for regulatory applications. The method makes use of two data sets: (i) the chemical composition of the atmospheric aerosol at a given measurement site and (ii) the chemical composition of the aerosol emitted from the principal sources in the region, presumed known. The method has been well-summarized by Watson et al. (1991) and is discussed in this section. Another frequently used approach, multivariate receptor modeling, makes use of atmospheric data to estimate not only the source contributions but compositions of...