Source and source strength determination of atmospheric organic acids

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(1) Concentrations of rain and dew organic acids such as formic, acetic and oxalic acids in the Hiroshima prefecture, western Japan, during 1995-1997 were determined by ion chromatography. Concentration range of formic, acetic and oxalic acids detected in rain and dew was 0-25,0-49 and 0-3.4mu M,respectivesy. The percentage of free acidity generated from organic acids to that from the total acidic substances was 2.9-7.1% and 14% in rain and dew, respectivesy, implying that organic acids contribute to the acidification of rain and dew.(2) Measurements of organic acid concentrations in car exhausts and combustion gases of incinerator were carried out to evaluate the role of anthropogenic activities in the production of atmospheric organic acids. The results indicate that these fossil fuel combustion gases contain from ppbv level to hundreds ppbv level of organic acids and the emission rates of these organic acids into the atmosphere are calculated to be from tons to hundreds tons per year in the Hiroshima fecture.(3) To elucidate the source and source strength of atmospheric organic acids, carbon stable isotopic ratio of organic acids was determined. Authentic samples of organic acids were first examined to determine if the change of isotopic ratio occurs during lon chromatographic separation and it was found to occur only minor isotopic ratio change. Thus the measurement of stable isotopic ratio of organic acids should be an useful method to determine the origin of organic acids.