Understanding of regional air pollution over China using CMAQ, part II. Process analysis and sensitivity of ozone and particulate matter to precursor emissions

Following model evaluation inpart I, this part II paper focuses on the process analysis and chemical regime analysis for the formation of ozone (O3) and particulate matter with aerodynamic diameter less than or equal to 10 mm (PM10) in China. The process analysis results show that horizontal transport is the main contributortothe accumulation of O3in Jan., Apr., and Oct., and gas-phase chemistryand vertical transport contribute to the production and accumulation of O3 in Jul. Removal pathways of O3 include vertical and horizontal transport, gas-phase chemistry, and cloud processes, depending on locations and seasons. PM10 is mainly produced by primary emissions and aerosol processes and removed by horizontal transport. Cloud processes could either decrease or increase PM10 concentrations, depending on locations and seasons. Among all indicators examined, the ratio of PHNO3=PH2O2 provides the most robust indicator for O3 chemistry,indicatingaVOC-limitedO3chemistryover mostof the easternChina in Jan., NOx-limitedin Jul., and either VOC- or NOx-limited in Apr. and Oct. O3 chemistry is NOx-limited in most central and western China and VOC-limitedin majorcitiesthroughout theyear.The adjustedgas ratio,AdjGR,indicates that PM formation in the eastern China is most sensitive to the emissions of SO2 and may be more sensitive to emission reductions in NOx than in NH3. These results are fairly consistent with the responses of O3