The role of traffic emissions in particulate organics and nitrate at a downwind site in the periphery of Guangzhou, China
Yi Ming Qin1, Hao Bo Tan2, Yong Jie Li3, Misha I. Schurman4, Fei Li2, Francesco Canonaco5, André S. H. Prévôt5, and Chak K. Chan1,4,61Department of Chemical and Biomolecular Engineering, Hong Kong University of Science and Technology, Hong Kong, China 2Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou, China 3Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau, China 4Division of Environment, Hong Kong University of Science and Technology, Hong Kong, China 5Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232, Villigen PSI, Switzerland 6School of Energy and Environment, City University of Hong Kong, Hong Kong, China
Received: 07 Feb 2017 – Accepted for review: 14 Mar 2017 – Discussion started: 15 Mar 2017
Abstract. Particulate matter (PM) pollution on the peripheries of rapidly expanding megacities in China can be as serious as in the cities due to direct emission and transport of primary PM from cities and effective formation of secondary PM. To investigate the emission and formation of PM on the periphery of Guangzhou (a megacity in southern China), a suite of real-time instruments were deployed at Panyu, downwind of Guangzhou, for PM measurements from November to December 2014. Dominated by organics, PM1 (particles with diameter less than 1 μm) concentrations in Panyu were higher (average ~ 55.4 μg/m3) than those in nearby cities such as Hong Kong and Shenzhen. Five sources for organic aerosols (OA) were resolved by positive matrix factorization (PMF) analysis with the multilinear engine (ME-2). These sources are hydrocarbon-like organic aerosol (HOA), cooking organic aerosol (COA), biomass burning related organic aerosol (BBOA), as well as semi-volatile oxygenated organic aerosol (SVOOA) and low-volatile oxygenated organic aerosol (LVOOA). The use of the COA mass spectrum obtained in our earlier study at a urban site in Hong Kong as a constraining factor in ME-2 produced the most interpretable results for the Panyu dataset. Freshly emitted HOA contributed 40 % to the high concentrations of organics at night. The mass concentration of SOA (SVOOA + LVOOA) continuously increased as odd oxygen (Ox = O3 + NO2) increased during daytime, attributable to the secondary production of PM facilitated by photochemistry. The SOA-to-Ox ratio was higher than those reported in previous studies in North America (covering the period from spring to summer), indicating efficient photochemical production of SOA even in late autumn and early winter at this subtropical downwind site. The efficient SOA formation during daytime was likely fueled by the sufficient SOA precursors in the atmosphere. The large input of NOx, which tracked well with HOA from automobile emissions, resulted in the significant formation of nitrate in both daytime and nighttime. Strong correlations between particulate nitrate and excess ammonium ([NH4+]/[SO42−] − 1.5) × [SO42−]) were observed. Higher partitioning of nitrate into the gas phase was found in November than in December, likely due to the lower temperatures in December. Results from this study suggest that there is much room to mitigate the PM pollution in urbanized areas such as Guangzhou, as well as their peripheries, by reductions in traffic-related pollutants.
Qin, Y. M., Tan, H. B., Li, Y. J., Schurman, M. I., Li, F., Canonaco, F., Prévôt, A. S. H., and Chan, C. K.: The role of traffic emissions in particulate organics and nitrate at a downwind site in the periphery of Guangzhou, China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-116, in review, 2017.