Elemental compositions and sizes of carbonaceous fly ash particles from atmospheric deposition collected at Cape Hedo, Okinawa, Japan: Implications for their long-range transportation and source region variation

Abstract

Spheroidal carbonaceous particles (SCPs) are a type of carbonaceous fly ash resulting from high-temperature industrial fossil fuel combustion. In this study, we examined the fluxes, elemental compositions (18 elements including silicon, sulfur, and aluminum but not carbon) and sizes of dry-deposited SCPs in the atmosphere at Cape Hedo (the northernmost part of Okinawa Island) to assess the temporal variation. The study site at Cape Hedo is suitable for investigating atmospherically deposited SCPs, particularly for evaluating their long-range transportation, because Cape Hedo is situated in an outflow region of East Asian pollutants. High SCP fluxes mostly occurred in autumn and winter when air masses came from the Asian continent. Additionally, we determined the temporal variations in the elemental compositions and the sizes of the SCPs during four week-long sampling periods and these results suggest that the high SCP fluxes were due to the transportation of the particles from the Asian continent to the study site. The potential source regions of the particles during respective periods are very consistent with the backward air mass trajectories. Results of our study would imply that sources of the SCPs deposited in the area changed temporarily, and that coarse particulate-pollutants such as SCPs were transported from the eastern Asian continent to Okinawa Island during the periods under specific meteorological conditions. Our findings suggest that the examination of SCPs from atmospheric deposition can contribute to the assessment of atmospheric transportation, specifically for particulate pollutants in the atmospheric boundary layer.