Research Projects

Project at a Glance

Project Status: complete

Title: A survey of acid precipitation in northern California

Principal Investigator / Author(s): McColl, John G

Contractor: Department of Soils and Plant Nutrition, UC Berkeley

Contract Number: A7-149-30


Research Program Area: Atmospheric Processes

Topic Areas: Acid Deposition


Abstract:

The acidity of rain has been increasing in the N.E.-U.S.A. and elsewhere (e.g., Scandinavia) and is having adverse ecological effects. Relatively little is known about the chemical composition and acidity of atmospheric precipitation and subsequent effects in the western U.S.A., and thus this study was conducted to monitor the chemical characteristics 'of atmospheric precipitation in California. Wet and dry precipitation were monitored on an event basis at the following eight locations during the wet season, November 1978 through May 1979; Berkeley and San Jose (pollution source areas in the San Francisco Bay area), Davis and. Parlier (in the central valley, agricultural areas), Hopland and Napa (coastal ranges, agricultural and range lands), Challenge (lower Sierran forest), and Tahoe City (on the shore of Lake Tahoe). Acid rain (pH < 5.6) was common at all eight sites. Mean pH of storms varied from 4.42 at.San Jose to 5.20 at Davis, and the lowest pH of any storm was 3.71 at San Jose. The primary cause of the acidity was probably the air pollutants NOx and SOx, following their dissolution in wet precipitation. NO3- was the anion most closely correlated with H+, and nitrogen generally occurred in greater amounts than sulfur. Appreciable quantities of dry deposition were also measured, but more research is heeded in procedures for quantifying dry atmospheric deposition. Although NO3 concentration (jig/1) and acidity (H concentration, Ug/1) of wet precipitation were greatest in pollution source areas, total deposition (kg/ha) of NO- and H+ were greatest in the non-urban receptor areas of Napa and Challenge; this was largely a function of the greater precipitation volumes at these two sites. Thus ecological effects' may be expected in the coast ranges, Napa valley and Sierras within the general west-to-east "wash-out fan" of wet precipitation, as well as within pollution source areas. The concentrations of both Cl- or Na+ in wet precipitation were found to be highly predictable functions of distance from the ocean, and provided useful tools to predict the contribution of oceanic salts at sites up to 280 km inland. Continued monitoring of atmospheric deposition in the western states should be made through interagency cooperation. Research efforts should also be encouraged to elucidate effects of "acid rain" on soil, water and plant resources, as the problem appears to be widespread and is likely to increase in severity.


 

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