Dimensions of the Los Angeles SO_2/sulfate problem

Abstract

Sulfur dioxide emission trends are reviewed in relation to sulfur dioxide air quality in the Los Angeles area. Emission fluctuations over the 19-year period from 1956 through 1974 are explained in terms of emission control policy changes. Simple statistical tests indicate that measured SO_2 air quality levels at Long Beach and downtown Los Angeles track changes in emission strength at nearby sources and from sources with low effective stack height. Atmospheric oxidation of SO_2 to form particulate sulfates is discussed. Sulfate air quality measurements at Los Angeles show a broad summer seasonal peak in all years of record, with isolated periods of very high sulfate concentration in some winters of record. The geographic distribution of long term average sulfate concentrations is examined and found to be rather uniform across existing monitoring stations in the Los Angeles Basin. Fluctuations in measured sulfate values from day to day are shown to track changes in inversion height, relative humidity, total suspended particulate levels, and ozone concentrations. From these relationships, it is suggested that day-to-day fluctuations in sulfate concentration are driven mainly by changes in SO_2 to sulfate reaction rate and by changes in the effective mixing volume of the air basin.