Transboundary transport of anthropogenic sulfur in PM2.5 at a coastal site in the Sea of Japan as studied by sulfur isotopic ratio measurement

Sulfur isotopic ratios (delta S-34) in size separated aerosol particles (PM2.5 and coarse particles) were measured at Niigata-Maki facing the Sea of Japan. Non-sea salt delta S-34 (delta S-34(nss)) in PM2.5 showed seasonal variations with relatively high values in winter (1.0-3.9% in spring, 2.8-4.5% in summer, 1.3-4.5% in autumn, 3.7-5.7% in winter). Taking into consideration air mass transport routes, delta S-34(nss) in the air masses which originated in the Asian continent and were transported over the Sea of Japan to the monitoring sites were higher than those values for air masses which were transported over the Japanese islands after leaving the Asian continent for each season. Considering that the delta S-34(nss) in sulfuric acid derived from domestic emissions in Japan are lower than those of delta S-34(nss) in coal, the lower delta S-34(nss) for the air mass transported over the Japanese islands suggest that sulfuric acid in PM2.5 modified the delta S-34(nss) due to aerosol mixing with sulfuric acid in Japan. Material balance calculations suggested that the relative contribution of transboundary transport in winter was also higher than for other seasons (40-75% in spring, 51-63% in summer, 45-73% in autumn, and 53-81% in winter). In particular, the contribution to the air masses which were transported directly from the Asian continent was relatively large (75% in spring, 59% in autumn, 78% in winter) in comparison with that for the air masses which were transported over Japan. (C) 2016 Elsevier B.V. All rights reserved.