Investigation of aerosol direct effects on meteorology and air quality in East Asia by using an online coupled modeling system

Abstract

Air pollution problems in East Asia are now critical. One issue attracting much attention is the high level of aerosol loading, so that, aerosol effects on climate and air quality are more significant than in other regions. These effects can substantially influence air quality prediction. Thus, it leads to a need to apply online models for climate and air quality simulations in this region. In this study, an online coupled meteorology and air quality modeling system composed of the Weather Research and Forecasting (WRF) model and the Community Multiscale Air Quality (CMAQ) model was applied for the purpose of evaluating the impacts of aerosol direct effects on meteorology and air quality in East Asia. Simulations were carried out in both one-way and two-way online (without and with the aerosol direct effects) for the whole historical year 2014 at a horizontal resolution of 45 km × 45 km. The model showed a good performance in reproducing the observations as well as capturing the spatial and temporal fluctuation of meteorological variables and air pollutant concentrations. On average, due to aerosol direct effects, shortwave radiation (SWR), temperature (T), planetary boundary layer height (PBLH), and wind speed (WS) were decreased by −7.71%, −0.42 °C, −8.13% and −1.00%, respectively; PM2.5, SO2, and NO2 concentrations were increased by +6.26%, +4.91%, +7.48%, respectively; while O3 concentration was decreased by −3.12% over China, Korea, and Japan for the entire year. Analyzing the cause-effect relationships among the responses of the above selected meteorological variables and air pollutants indicated that the reduction in SWR at ground surface caused by aerosol direct effects produces a decrease in T and PBLH, leading to an increase in PM2.5 concentration and a decrease in O3 concentration. Aerosol direct effects also affected long-range transport of PM2.5 from the continent to downwind area. Investigation of eastward response of PM2.5 to aerosol direct effects revealed that the amount of long-range transported PM2.5 was decreased in downwind area due to the impact of aerosol direct effects. It was mainly attributed to the increase in dry deposition of PM2.5 precursors and the decrease in WS in the continent. The results of study highlighted that the aerosol direct effects play an important role in the atmospheric dynamic and chemistry and cause considerable impacts on East Asia air quality.