Chemical element balances and identification of air pollution sources.

Air pollution sources of given types, whether natural or man-made, emit a characteristic set of chemical elements in approximately fixed proportions. If the sources in a polluted region are known, the contributions from each source can be estimated by measuring elemental concentrations at a given point and solving a set of simultaneous linear algebraic equations. The method has been applied to the particulate matter measured in the air of Pasadena over an 11-hr period and averaged over particle size. For the period in question, about 15% of the particulate matter resulted from primary natural sources and 25% from primary man-made sources. About 40% of the total results from atmospheric reactions with one quarter produced by the conversion of gas phase hydrocarbons to particulate form. The estimate for this figure is based on a carbon balance. Altogether, about 70% of the total particulate burden has been accounted for with water probably making up a significant portion of the missing 30%. Improvements and extensions of the method are discussed.