Impact of national NOx and SO2 control policies on particulate matter pollution in China

China's air pollution control policies during the 12th Five Year Plan (2011-2015) are characterized by the targets of 10% nitrogen oxides (NOx) reduction and 8% sulfur dioxide (SO2) reduction from the 2010 levels. In this study, the Community Multi-scale Air Quality (CMAQ) modeling system was used to evaluate the impact of only SO2, only NOx, and joint SO2/NOx control measures on particulate matter pollution, the greatest concern for urban air quality in China. Four emission scenarios were developed for 2015, including a business-as-usual scenario, a reference NOx control scenario based on the governmental plan, an accelerated NOx control technology scenario, and a scenario assuming joint controls of NOx and SO2 based on the governmental plan. Under the planned NOx control measures, the annual mean concentrations of particulate matter less than or equal to 2.5 mu m (PM2.5) decline by 1.5-6 mu g m(-3), i.e. 1.6%-8.5%, in the majority of eastern China. The largest reduction occurs in the middle reach of the Yangtze River. Under accelerated NOx control measures, the annual average PM2.5 concentration reductions (compared with the business-as-usual scenario) in eastern China are 65% higher than the reductions under planned control measures. The unusual increase of PM2.5 concentrations in the North China Plain and the Yangtze River Delta Turing January after the reductions of NOx emissions was an integrated effect of excessive NOx, the ammonia-rich inorganic aerosol chemistry, and the non-methane volatile organic compounds (NMVOC) sensitive photochemical regime. Under the joint controls of NOx and SO2, the annual mean PM2.5 concentrations decline over 3 mu g m(-3), i.e. 3.2%-13%, in the majority of eastern China, and some areas in the middle reach of the Yangtze River have reductions as large as 6-8.3 mu g m(-3), i.e. 5.0%-13%. The average PM2.5 concentration reductions in eastern China are 1.20 mu g m(-3), 3.14 mu g m(-3), 3.57 mu g m(-3), 4.22 mu g m(-3) in January, May, August, and November, respectively. The corresponding declining rates are 2.3%, 12.2%, 14.3%, and 8.1%, respectively. More stringent policies should be implemented in winter to reduce the heavy pollution periods. The annual average PM2.5 concentration reductions in three major city clusters are comparable with the average reductions of eastern China. Stringent regional control policies are required for the significant improvement of particulate air quality in major city clusters. (C) 2013 Published by Elsevier Ltd.