Trends in Historical Acid Precursor Emissions and Their Airborne and Precipitation Products

Abstract

The paper discusses historical bulk deposition data and ambient air quality data for sulfate and nitrate in relation to estimated changes in sulfur dioxide and nitrogen oxide emissions since the turn of the century. The study focuses on the northeastern United States and southeastern Canada. The quality of available data, segregated into pre-1955 and post-1955 periods, is surveyed. The early period before the 1950s provides much less reliable information than later data. Inspection of the data indicates that, in broad terms, changes in precipitation sulfate and nitrate qualitatively follow patterns of emission change, with declines in sulfate and increases in nitrates. Long-term continuous records of precipitation sulfate show distinct geographical differences so that no single station can be used to infer regionwide trends. Data records suggest that the changes in precipitation sulfate between 1965 and 1980 at rural sites in central New York State and New Hampshire were more influenced by SO/sub 2/ emission changes in nearby source regions rather than by those in more distant source regions. At other sites in western New York and north central Pennsylvania, no proportional relationship was found between emissions and precipitation sulfate during the same period. These results indicate that the hypothesis ofmore » a linear proportionality between SO/sub 2/ emissions and sulfate deposition is not uniformly supported, and that, to the extent it exists, it should be more applicable to SO/sub 2/ emissions from relatively nearby sources in the Northeast. In addition, if sulfate is the principal anion responsible for bulk deposition acidity, the sulfate trends do not support the hypothesis that acidity has increased in recent years in the eastern United States. 55 references.« less