Measurements of atmospheric SO2 and SO42−, and determination of the wet scavenging coefficient of sulfate aerosols for the winter monsoon season over the sea of Japan

Abstract In order to determine the scavenging coefficient of oxides of sulfur in winter monsoon over the Sea of Japan both air and precipitation concentrations of sulfur dioxide and sulfate were measured on Sado Island on the Sea of Japan coast. The measurements were taken during the period between 28 January and 3 February 1992. The atmospheric concentrations of SO 4 2− were 0.57–1.11 μg S m −3 whereas those of SO 2 , were below 0.27 μg S m −3 , much lower than SO 4 2− concentration. A back trajectory analysis showed that these sulfur species would have been transported from Eurasian continent over the Sea of Japan. A layer-average scavenging coefficient, k , for sulfate by precipitation including snow, graupel and rain was determined on the basis of the equation k = HP / h , where H , P and h are the scavenging ratio, precipitation intensity and mixing layer height, respectively, under the assumption of a uniformly mixed layer over the warm sea current along the Sea of Japan coast. The scavenging coefficients were calculated to be 3.5 × 10 5 −2.9 × 10 −4 S −1 for precipitation intensities of 0.13–3.1 mm h −1 . A regression analysis of these datasets gave a k value for submicron SO 4 2− aerosol over the Sea of Japan of k = 1.38 × 10 −4 P 0.74 , where p is precipitation intensity. These values are very close to a recently obtained result by Jylha for radioactive aerosols. Summarizing the measurements taken by the authors and other investigators the wet scavenging coefficient k may be represented by k = aP b where a is around 10 −4 , and b is between 0.67 and 0.76.