Simulation of the transition metal-based cumulative oxidative potential in East Asia and its emission sources in Japan

Abstract

The aerosol oxidative potential (OP) is considered to better represent the acute health hazards of aerosols than the mass concentration of fine particulate matter (PM_2.5). The proposed major contributors to OP are water soluble transition metals and organic compounds, but the relative magnitudes of these compounds to the total OP are not yet fully understood. In this study, as the first step toward the numerical prediction of OP, the cumulative OP (OP_tm*) based on the top five key transition metals, namely, Cu, Mn, Fe, V, and Ni, was defined. The solubilities of metals were assumed constant over time and space based on measurements. Then, the feasibility of its prediction was verified by comparing OP_tm* values based on simulated metals to that based on observed metals in East Asia. PM_2.5 typically consists of primary and secondary species, while OP_tm* only represents primary species. This disparity caused differences in the domestic contributions of PM_2.5 and OP_tm*, especially in large cities in western Japan. The annual mean domestic contributions of PM_2.5 were 40%, while those of OP_tm* ranged from 50 to 55%. Sector contributions to the OP_tm* emissions in Japan were also assessed. The main important sectors were the road brake and iron–steel industry sectors, followed by power plants, road exhaust, and railways.