A Study of Regional Air Pollution in Spring using WRF/CMAQ Model over Pearl River Delta, China

As one of the three large economic regions of China, the regional air pollution, in which the primary is aerosol pollution, is serious over Pearl River Delta (PRD) region, China. In this study, WRF/CMAQ model was utilized to study regional air pollution in spring over PRD. Model performance was examined and evaluated by comparison with observations over PRD for a 28-day period from 1 to 28 March 2012. WRF model shows reasonable performance for major meteorological variables (i.e., temperature, relative humidity, wind speed) with correlation coefficient of 0.76-0.94. CMAQ model generally reproduces the spatial patterns and time series variations of air pollutions (SO2, NOX, O3, PM10 and PM2.5). The model successfully captured three air pollution episodes during 3-5 (episode one), 15-16 (episode two) and 26-27 (episode three) in this month. The primary air pollutants are particle matter during episode one and two and ozone during episode three, respectively. Higher ratios of PM2.5/PM10 and lower visibilities were simulated during episode one and two than those during episode three, which were consistent with the observations. The reason for these differences was the dominate weather system during the air pollution episodes. Episode one and two occurred with the south wind over PRD, the relatively humidity were high, which was benefit to the chemical conversion process, especially aqueous chemical reactions. The main components in particle matter are sulfate and nitrate, which were contributed to the ratios of PM2.5/PM10 and low visibilities. Different with episode one and two, the dominate wind was by north during episode three, the relatively humidity was 50% or so. The sulfate mass concentrations were lower than those during episode one and two.