Effects of the meteorological variability on regional air quality in East Asia

We examine the effects of the meteorological variability on O3 and SO42−–NO3−–NH4+ aerosol concentrations in East Asia using 3-D chemical transport model (GEOS-Chem) simulations for the period of 1985–2006. The model was driven by the GEOS assimilated meteorology with the emission estimates from the Streets et al. inventory with annual scale factors of Regional Emission inventory in Asia (REAS). Over the past two decades precursor emissions have been dramatically increased. Our model simulations however show strong non-linear responses of oxidation products to the increases of those precursors. The analysis of simulated results shows significant effects of meteorological variability on O3 and SO42−–NO3−–NH4+ concentrations. Springtime O3 concentration has been generally increased over the past two decades mainly due to increases in anthropogenic precursors emissions but concurrent changes in meteorology including decreases of cloud covers and increases of temperature further enhance O3 increases in East Asia. Our analysis reveals that changes in meteorology account for 30% of total O3 increases in East Asia over the past two decades. On the contrary, increases in mixing depth suppress increases of (NH4)2SO4 concentrations in summer but decreases in mixing depth in winter result in enhancement of NH4NO3 aerosols concentrations up to 4 μg m−3 in eastern China. Effects of meteorological variability on SO42−–NO3−–NH4+ aerosol concentrations are thus seasonally dependent such as a decrease in summer by 4% but an increase by 7% in winter over the past two decades. This result indicates that the meteorological conditions have changed more favorable for the PM air quality degradation in winter.