[Impacts of Online Measurements of Organic Molecular Markers as Input Species for PM2.5 Source Apportionments: A Case Study in Hangzhou During the 19th Asian Games].

Abstract

Positive matrix factorization （PMF） is one of the most widely used receptor models for PM_2.5 source apportionment. The traditional PMF method generally uses inorganic （such as nitrate, sulfate, and EC） measurement data as input species to apportion PM_2.5 sources. These species have ambiguous source origins； thus quantifying PM_2.5 sources with high source sectors is difficult. In this study, online measurements of major chemical components, elemental tracers, as well as organic molecular markers were applied in a PMF model to investigate the differences between the major chemical components-based PMF （MCC） and organic molecular markers-based PMF （OMM） methods in terms of source identification, source separation, and source quantification. The results showed that with the input of organic molecular markers （such as polycyclic aromatic hydrocarbons, fatty acids, dicarboxylic acids, hydroxyl-dicarboxylic acids, C₉ acids, and phthalic acid）, the OMM method greatly enlarged the number of source factors identified. Further, industry emission, shipping emission, dust, vehicle emission, biomass burning, secondary nitrate, and secondary sulfate； two primary source factors （coal combustion and cooking emission）； and four secondary organic aerosol （SOA） source factors were also resolved in the OMM method. Comparing with the source profiles resolved by the MCC method, we found that OC/EC mass ratios in OMM-resolved source profiles of industry emission, vehicle emission, biomass burning, and coal combustion were closer to those obtained from emission inventories. In terms of source quantification, the mass contributions of vehicle emission and biomass burning resolved by the MCC method were notably higher than those resolved by the OMM method, especially under high O₃ concentrations （> 120 μg·m^-3）. This suggests that without the input of specific organic molecular markers, the MCC method was inclined to apportion parts of secondary source contributions into primary sources （such as vehicle emission and biomass burning）. We further quantified and compared PM_2.5 source contributions in Hangzhou before, during, and after the 19^th Asian Games with the application of the OMM method. Our results showed that the percentage contributions of vehicle emission, industry emission, and dust dropped by 65%, 24%, and 24%, respectively, during the Games. Anthropogenic SOA and aged SOA also displayed significant decreases in mass contributions during the Games by 35% and 49%, respectively, due to the emission reduction of volatile organic compounds （VOCs）. These results imply that PM_2.5 pollution can be effectively controlled with the implementation of emission reduction measures. Our study also revealed that online measurements of organic molecular markers are important for improving PM_2.5 source apportionment results and formulating pollution control policies.