Carbonaceous aerosol composition over various regions of China during 2006

Abstract

The elemental (EC) and organic carbon (OC) fractions of ambient aerosols were determined by thermo‐chemical analysis of 24‐h samples collected during 2006 at 18 stations in China located at various rural, urban and remote locations. The annual mean concentration levels are found to be 0.35 ± 0.01 μg EC m−3 and 3.0 ± 0.21 μg OC m−3 for the remote background sites; 3.6 ± 0.93 μg EC m−3 and 16.1 ± 5.2 μg OC m−3 for the regional sites; and 11.2 ± 2.0 μg EC m−3 and 33.1 ± 9.6 μg OC m−3 for the urban sites, respectively. At rural sites representing regionally dispersed aerosols, levels are comparable to other locations in Asia. At all sites, both EC and OC show a consistent seasonal variation with a peak in winter, dropping in spring, reaching a minimum in summer and then increasing in autumn. The ratio of OC to EC is on the order of 3 for the urban locations, but can reach as high as 6 at the rural sites. This may partly be due to the open biomass burning in field of rural area, but may also indicate the presence of a regional background of secondary organic carbon (SOC) in China. These high ratios of OC/EC complicate the assessment of the climatic impacts of carbonaceous aerosols in China, as optical scattering from the high OC concentrations may lead to a cooling effect that counteracts the possible warming caused by EC optical absorption.