Development of a framework for a high-resolution, three-dimensional regional air quality simulation and its application to predicting future air quality over Japan

We have developed a framework for a three-dimensional regional air quality simulation that is applicable to various air quality studies over Japan. The framework consists of the following simulation model systems: the Weather Research and Forecasting (WRF) model to simulate meteorological fields; the Community Multi-scale Air Quality (CMAQ) modeling system to simulate pollutant concentrations; emissions estimate models; and emission databases. Motor vehicle emissions in Japan are estimated using the Japan Auto-Oil Program (JATOP) vehicle emissions estimate model; anthropogenic emissions from sources other than motor vehicles in Japan are estimated using the Georeference-Based Emission Activity Modeling System (G-BEAMS); and biogenic emissions are estimated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). The Regional Emission inventory in Asia (REAS) is used for emissions in Asian countries except for Japan. The most prominent feature of our framework is its ability to simulate multi-scale air quality. The framework allows for the simulation of emissions and the dynamic transport of pollutants in heavily polluted urban areas with a maximum resolution of 1×1km, and the long-range transport of pollutants is also taken into account. This framework is used to analyze the impact of future emissions from anthropogenic sources on air quality over the Tokyo metropolitan area. NOx, NMVOC and primary PM2.5 emissions over the Tokyo metropolitan area are estimated to be reduced by 44.5%, 18.1% and 41.7%, respectively, from 2005 to 2020. The simulation predicts that concentrations of NO2 and PM2.5 over the Tokyo metropolitan area will decrease by approximately 30–40% and 15–20%, respectively, during the above period. O3 concentrations significantly increase in winter due to decreased titration by NO, whereas no significant variations are observed in spring and summer. In addition, we analyzed the impact of future long-range transport projected under three emission scenarios provided by REAS. The simulation indicates that future long-range transport will affect concentrations of O3 and PM2.5 over the Tokyo metropolitan area; however, its impact is small compared with that of future anthropogenic emissions in Japan. ► A framework for a high resolution, 3-D air quality simulation was developed. ► The performance of the simulation is well over Tokyo. ► The air quality over Tokyo will be improved further by existing regulations. ► Domestic emissions a