Regional modeling of organic aerosols over China in summertime

Abstract

A comprehensive aerosol model was developed and incorporated into a regional air quality model system (RAQMS). It was used to study the behavior and the regional characteristics of carbonaceous aerosols over China in summertime with focus on organic carbon aerosols (OC), especially the secondary organic carbon aerosol (SOC). The whole month of July and August 2003 were selected as simulation period when biogenic volatile organic compounds (VOCs) emitted from vegetation reach the annual maximum. A number of measurements for organic and elemental carbon (EC) aerosols were conducted simultaneously over China during this period, which allow for a rigorous evaluation of model performance and an in‐depth investigation of organic aerosols. The comparison of model results with observations indicates that the developed model system is able to represent the atmospheric oxidative capacity and the major evolutionary features of OC and EC reasonably well, but a tendency was found toward underprediction of both OC and EC aerosols. Sensitivity simulations regarding absorbing matter for condensation (AMC) and enthalpy of vaporization (EOV) were conducted to understand the effects of key factors on secondary organic aerosol (SOA) formation and to provide possible ranges of SOA yields in the troposphere of East Asia. It is found that the overall SOA formation tends to increase with increasing EOV and AMC, but the sensitivity of SOA formation to EOV depends on ambient temperature as well. High OC concentrations mainly occurred in the areas along the Yangtze River, in central China and most parts of north China including Beijing and Tianjin districts, with the maximum monthly mean as high as 15 μg m−3. SOC concentration was high in the forest areas of southeastern, southwestern and northeastern China, with maximum concentration exceeding 5.0 μg m−3 to the south of the Yangtze Delta. The contribution of SOC to OC is around 50% in these areas, whereas in the broad areas north of the Yangtze River, primary organic carbon aerosol (POC) accounts for a high fraction of the total OC (>60%). The estimated regional burdens of EC, OC, POC, and SOC for base case are 28.13, 61.16, 46.05, and 15.11 Gg, respectively. Of the SOC burden, contributions from oxidation of anthropogenic aromatics, monoterpene and isoprene are 17% (2.58 Gg), 48% (7.32 Gg) and 35% (5.21 Gg), respectively. The regional SOC burden varies from 15.1 to 40.3 Gg in different scenarios. For the base case, the total burdens of EC, OC, POC and SOC are estimated to be 13.8, 37.3, 25.6, and 11.8 Gg, respectively, while using emissions solely from China (20°N∼50°N and west of 100°E) in model simulation.