Impact of energy and vehicle transformation through 2050 on atmospheric PM2.5-metals concentration and aerosol acidity that induce respiratory inflammation in Japan; focus on the changes in exhaust/non-exhaust and upstream emissions

Transition metal components in PM_2.5 induce inflammation of the respiratory system. The increase in aerosol acidity due to gaseous pollutants promotes metal dissolution and contributes to redox activation. In this study, the impact of renewable energy shifting, passenger car electrification and light-weighting on atmospheric concentration of PM_2.5 total mass, Fe, Cu, Zn and aerosol acidity in Japan over 2050 was evaluated using a regional meteorology-chemistry model. The primary emissions of PM_2.5, Fe, Cu, and Zn were reduced by 9%, 19%, 18% and 10%, and their surface wide-area concentrations decreased 6 – 8%, 10 – 12%, 16 – 18% and 2 – 4%, respectively. On a PM_2.5 mass basis, battery electric vehicles (BEVs) have been considered to have no advantage in non-exhaust PM emissions because the increased tire and road wear and resuspension due to their heavy weight offset the benefit of brake wear reduction by regenerative brake. Indeed, passenger car electrification without light-weighting also did not significantly reduce total primary PM_2.5 emissions in Japan in this study (-1.4%), but was highly effective in reducing metals, especially Fe and Cu (-6.7% and -11.4%, respectively). Furthermore, this study estimated that even tire and road wear and resuspension could be reduced if the drive battery and body frame were light-weighted, and the benefit would be larger. Therefore, vehicle electrification (mainly BEVs) and light-weighting could be one of the effective means of reducing the risks of respiratory inflammation. The renewable energy shifting reduced SO_x and NO_x emissions from thermal power plants and decreased aerosol acidity near power plants (approximately pH +0.2), while the passenger car electrification reduced NO_x and NH₃ emissions and slightly increased aerosol acidity in urban, as a result of acid-base balance (in July, approximately pH -0.1 – -0.2). However, anyway, the sensitivity of water-soluble metal concentrations was mostly dependent on changes in primary metal emissions and little affected by changes in aerosol acidity (0 – +2% for Fe, 0 – +0.5% for Cu and Zn). Therefore, it was suggested that primary emission control of metals is more important than gaseous pollutants in reducing water-soluble metal concentrations.