Study On Reduce The Influence Of Secondary Organic Carbon On Source Apportionment Of Ambient Particulate Matter

The chemical mass balance (CMB) model, which is based on the principle of mass conservation, is one of several receptor models that have been applied to source apportionment of ambient particulate matter, and has been widely used. However, the presence of secondary organic carbon (SOC) brought uncertainties to the results of source apportionment. SOC, which is formed through atmospheric oxidation of volatile organic compounds, isn’t emitted directly from primary sources. It was very difficult to identify the SOC source profile for CMB model. Therefore, SOC made the matching degree of carbon species between identified sources and receptor decreased, and resulted in the source contributions calculated from CMB model had larger uncertainties. SOC, which influenced the reliability of CMB model, has been a difficult problem for a long time.In this study, we focused on the problem that SOC source profile was difficult to be obtained, and put forward a new method to solve this problem. The content of this method included:Using "OC/EC minimum ratio" method to estimate SOC concentration, reconstructing new receptor profile based on SOC concentration, and modifiying CMB model. New receptor profile made carbon species in receptor match well with those in identified sources. This method reduced the influence of SOC on CMB model results, and provided a useful technique to solve the source apportionment of secondary organic particulate matter.Because there wasn’t any analytical technique for directly measuring SOC concentrations, several indirect methods have been applied to estimate SOC. However, each indirect method had its own limitation, and it was hard to quantify SOC. And due to lack of standard carbon analysis method (especially defining the deviding point of OC and EC), different carbon analysis methods gave in different OC and EC concentrations. In this paper, the results of carbon species measured by elemental analysis (EA) method and thermal-optical reflection (TOR) method were compared. The uncertainties of SOC estimation caused by carbon analysis method had been discussed. Based on the relationship of measurement results obtained from these two methods, we put forward an idea about that the content of organic pyrolyzed carbon (OP) obtained from TOR method might be applied to revise the OC concentration measured from EA method.The modified CMB model was applied to source apportionment of Kaifeng, Wuxi and Panzhihua city. The comparisons of results calculated from modified CMB and traditional CMB model were also conducted, and showed that the source contributions of modified CMB model were more reasonable than that calculated from traditional CMB model.