Long-term Monitoring of Metal Elements in Total Suspended Particle Aerosols Simultaneously Collected at Three Islands in Okinawa, Japan

Abstract

In the present study, total suspended particle (TSP) aerosols were simultaneously collected using identical high-volume air samplers at three islands in Okinawa; Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS, Okinawa Island), from 2008 to 2012 Kume Island (KM, ca. 160 km south-west of CHAAMS), and Minami-Daitou Island (MD, ca. 320 km south-east of CHAAMS) from 2008 to 2010. The sample collected were analyzed using energy-dispersive X-ray fluorescence spectrometry (ED-XRF) and synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) to investigation long-range transport of metal elements to Okinawa from the Asian continent. From analytical data on samples collected at CHAAMS for five years, it was found that most elements (Ca, Fe, Ti, Mn, V, Cu, Ni, Pb, As, and Zn) in TSP aerosols showed higher concentrations in the period from October to May, when the continental air mass passed over Okinawa, regardless of Asian dust events. The annual average concentrations of Ni, Cu, Zn, As, Se, and Pb in TSP aerosol samples collected at three islands gradually decreased as the TSP aerosols traveled from west to east in any year. Based on the enrichment factors (EFs) and concentration ratios, it is considered that most of anthropogenic elements such as As, Pb, and Zn in TSP aerosols are derived from coal combustion in the Asian continent. Moreover, it is confirmed from the direction of the air mass reaching the sampling sites that Cu, Zn, As, and Pb in TSP aerosols were transported to the three islands in Okinawa by air mass not only from northwest and north, but also from the west. These TSP aerosols transported from the Asian continent may influences not only the atmospheric environment but also the concentrations of trace metals in coastal seawater in Okinawa, which have to be kept extremely low to preserve the diverse and unique ecosystem in coral reefs.

Keywords

• long-range transportation
• metal elements
• tsp aerosols
• okinawa
• asian continent