Model Study on the Distribution and Evolution of Major Aerosol Components in Eastern China in the Spring

A regional air quality model system (RAQMS) was applied to investigate the distribution of major aerosol chemical components in eastern China in spring 2009. The comparison of model results with observations at Taishan station indicates that the model system is able to represent the day-to-day variation of aerosol concentrations reasonably well. In general, the model simulates concentrations of inorganic aerosols well, but it tends to overpredict and underpredict black carbon and organic carbon aerosol concentrations, respectively, mainly due to the uncertainties in emission inventory, the chemical mechanism of secondary organic aerosol formation, and the model resolution. The model results show that near the surface, high aerosol concentrations mainly occurred in the Huabei Plain, the east of Sichuan Province, in the middle and lower reaches of the Yangtze River. The organic carbon aerosol concentrations in the southern parts of Yunnan and Guangxi provinces were larger than those in other regions of China, due to the transport effect of biomass burning emissions from Southeast Asia. Soil dust was rich in northwestern China and can be transported toward eastern China and portions of southern China. The PM_2.5 (the particulate matter with aerodynamic diameter smaller than 2.5 micrometers) levels in the Huabei Plain, east of the Sichuan Province and the middle and lower reaches of the Yangtze River, were seriously high, exceeding the daily mean PM_2.5 limit of the national standard. Both observations and model simulations showed that nitrate exceeded sulfate concentrations at Taishan station. The regional burden of nitrate within the troposphere in northern China was close to or in excess of that of sulfate, whereas in southern China, the opposite was the case; this was associated with the distribution of clouds in spring (there are more clouds in southern China at that time than that in northern China) and the relevant aqueous chemical mechanisms, as well as the different temperature effects on aerosol formation. For eastern China, although the burden of sulfate (46 Gg) still exceeded that of nitrate (42 Gg), they became very close, reflecting the rapid increase in emissions of nitrogen oxides in China. During the study period, the regional burden of PM₁₀ (the particulate matter with aerodynamic diameter smaller than 10 micrometers) was 990.8 Gg, and the major chemical components of PM₁₀ were 52.6 Gg (sulfate), 48.2 Gg (nitrite), 32.1 Gg (ammonium), 22.9 Gg (black carbon), and 74.1 Gg (organic carbon). Primary organic carbon (POC) and secondary organic carbon (SOC) accounted for 60% and 40% of the total organic carbon (OC) burden, respectively. In eastern China, anthropogenic aerosols and dust aerosols accounted for 30% and 70% of the total PM₁₀ burden, respectively, indicating the important contribution of dust to airborne aerosol mass in China in the spring.