Spatial and temporal variations of chemicals in the TSP aerosols simultaneously collected at three islands in Okinawa, Japan

摘要

East Asia's rapid economic growth has led to concerns about the emission of air pollutants. We collected total suspended particle (TSP) aerosol samples simultaneously at three islands in Okinawa, Japan, which are downwind of East Asia, during the Asian dust season, to examine the spatial and temporal variations and chemical transformations of major chemicals in the aerosols. Weekly samples were collected from July 2008 to June 2010, and the concentrations of water-soluble cations, anions, and organic carbon (WSOC) were determined (n = 303). Spatial distribution analysis showed that monthly mean concentrations of non-sea-salt (nss)-SO_4~(2-) in the spring (Asian dust season) decreased with increasing distance from Asia, while the trend for NO_3~- was less evident, suggesting that chemical transformation affected the long-range transport of certain chemicals. Temporal variation analysis showed that concentrations of nss-SO_4~(2-), NO_3~-, and WSOC during the spring were about 2.0, 2.4, and 1.8 times those in the summer (cleaner air mass from the Pacific Ocean), respectively. This study demonstrated that air pollutants were transported from the Asian continent to the Okinawa islands and affected the air quality in the region. There may also be impacts on ecosystems, because increased concentrations of particulate NO_3~- could increase nutrient levels around the Okinawa islands.