Characteristics and the origins of the carbonaceous aerosol at a rural site of PRD in summer 2006
1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
2Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan
3Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan
4Air Quality Research Center, University of California, Davis, CA 95616, USA
Abstract. Both organic carbon (OC) and elemental carbon (EC) were measured at a rural site, Back Garden (BG), 50km northwest of the Guangzhou City, by using a semi-continuous thermal-optical analyzer during PRIDE-PRD 2006 summer intensive campaign. Together with the online EC/OC instrument, multiple instruments were also employed here which provided a good opportunity to check data quality. The regressions between the mass of organic aerosol (OM) and OC, as well as OC and water soluble organic carbon (WSOC) imply reliability of the data measured in this campaign. The average OC concentrations in fine particle for three typical periods during the campaign (local emission influence, typhoon and participation, normal days) were 28.1 μg C m−3, 4.0 μg C m−3 and 5.7 μg C m−3, respectively, and EC were 11.6 μg C m−3, 1.8 μg C m−3, and 3.3 μg C m−3 orderly. Diurnal variations of EC and OC showed that there were two peaks for EC and OC concentrations, i.e. at night and early morning, which were probably caused by the primary emission accumulation when the boundary layer was shallow. Compare to the constant diurnal enhancement ratios of primary EC, the enhancement ratio of OC (OC versus (CO-CObackground)) remained in a relative high level in the afternoon with a similar diurnal variation to oxygenated organic aerosol (OOA), indicating the strong photochemical formation of OC. The traditional EC tracer method was modified to estimate the secondary organic carbon (SOC) formation, which shows that the average SOC concentration in BG site was about 2.0 ± 2.3 μg C m−3.The SOC fraction in OC reached up to 80 % with the average of 47 %. Good correlations between estimated SOC versus measured OOA or WSOC, and estimated POC versus measured hydrocarbon-like organic aerosol (HOA) also proved the reliable results by the modified EC tracer method in this paper.