Elucidation of the long distance transportation of sulfate ion from Asia Continent based on sulfur isotope

Precipitation was collected every 24 hours during Oct. 1994-Dec. 1995. Samples collected were measured their major chemical compositions and sulfur isotope ratio. Chloride ion concentration is lower than 2 ppm in May-August and increases up to 15 ppm on and after Septmber. However most of Na/Cl ratios of precipitation samples with Cl<1 ppm range 0.1-0.5 and are lower than that of sea water (0.56). This suggests that chloride ion with anthropogenic origin significantly contributes in summer. NssSO4 concentration is 0-2.5 ppm in May-August and on and after September it increased up to 5 ppm. NO3/nssSO4 ratio in ppm gradually decreases from May (0.7-1.2) to December (0.2-0.6). Delta S of nssSO4 is-1 to 3 per mill in May-July. Delta S values higher than zero suggest that even in summer season sulfate ion is transported from Asia Continent. Sulfur isotope ratio is 0-3 per mill in September and 0-7 per mill in November-December. This suggests that the contribution of SO4 with continental origin increase with the changes of seasons from fall to winter. Delta S versus NO3/nssSO4 ratio plot shows that most precipitation distribute between two end points. One end point, delta S of 5 per mill and NO3/nssSO4 of 0.2, is typical for coal fume exhausted from northern China. The other end point, delta S of-2 per mill with NO3/nssSO4 of 1.5, is common for petroleum combustion gas in Japan. This fact suggests that sulfate ion transported from Asia Continent is mixed with local sulfate ion with various ratios.