Using air trajectories to analyze the seasonal variation of aerosols transported to the Oki Islands

Aerosols transported to the Oki Islands were characterized by analyzing the relationship between air trajectories and the data for aerosol constituents recorded over a three-year period. In our simple model, the calculated air trajectories were classified into seven regional sectors and three special cases. The changes in the aerosol constituents during a given month were closely related to the variation in air masses arriving at the island during that month. Therefore, each monthly elemental concentration was expressed by the linear combination of the trajectory sector contributions and the representative elemental concentrations of these sectors. Taking into account wet removal on the elemental concentrations in the atmosphere, we then estimated the representative elemental concentrations in the air mass for each sector by solving these simultaneous equations for the data taken over the three years. We found that the variations in the elemental concentrations over the observed time period could be simulated very well by this rather simple model. This analysis revealed that (1) the Pb concentration was higher in the air from central China than from other areas, (2) the As concentration was higher in the air from the northern Asian continent, (3) the concentration of soil-related elements, such as Al and Mn, were very high in the air from central China, (4) non-sea-salt-sulfate and V were relatively high in the air from western Japan, which included the contribution from a volcano (Mt. Sakurajima). Such findings are consistent with previous observational data. This analysis provided a simple methodology for calculating the contribution of elemental concentrations in the air from a number of sectors; thus demonstrating the effectiveness of such an analysis in projecting future trends in the air quality around the Oki Islands.