Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implication for seasonal formation mechanism of Secondary Organic Aerosol (SOA)
Chunlei Cheng1,2, Mei Li1,2, Chak K. Chan3, Haijie Tong4, Changhong Chen5, Duohong Chen6, Dui Wu1,2, Lei Li1,2, Peng Cheng1,2, Wei Gao1,2, Zhengxu Huang1,2, Xue Li1,2, Zhong Fu7, Yanru Bi7, and Zhen Zhou1,21Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou 510632, China 2Guangdong Provincial Engineering Research Center for on - line source apportionment system of air pollution, Guangzhou 510632, China 3School of Energy and Environment, City University of Hong Kong, Hong Kong, China 4Max Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, Germany 5State of Environmental Protection Key Laboratory of the formation and prevention of urban air pollution complex, Shanghai Academy of Environmental Sciences, Shanghai 200233, China 6State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangdong Environmental Monitoring Center, Guangzhou, 510308, China 7Guangzhou Hexin Analytical Instrument Limited Company, Guangzhou 510530, China
Received: 01 Dec 2016 – Accepted for review: 15 Dec 2016 – Discussion started: 21 Dec 2016
Abstract. The formation of oxalic acid and its mixing state in atmospheric particulate matter (PM) were studied using a single particle aerosol mass spectrometer (SPAMS) in the summer and winter of 2014 in Heshan, a supersite in the rural area of the Pearl River Delta (PRD) region in China. Oxalic acid-containing particles accounted for 2.5 % and 2.7 % in total detected ambient particles in summer and winter, respectively. Oxalic acid was measured in particles classified as elemental carbon (EC), organic carbon (OC), elemental and organic carbon (ECOC), biomass burning (BB), heavy metal (HM), secondary (Sec), sodium-potassium (NaK) and dust. Oxalic acid was found predominantly mixing with sulfate and nitrate during the whole sampling period, likely due to aqueous phase reactions. In summer, oxalic acid-containing particle number and ozone concentration followed a very similar trend, which may reflect the significant contribution of photochemical reactions to oxalic acid formation. Furthermore, favorable in-situ pH (2–4) conditions were observed, which promote Fenton like reactions for efficient production of •OH in HM type particles. A mechanism in which products of photochemical oxidation of VOCs partitioned into the aqueous phase of HM particles, followed by multistep oxidation of •OH through Fenton like reactions to form oxalic acid is proposed. In wintertime, carbonaceous type particles contained a substantial amount of oxalic acid as well as abundant carbon clusters and biomass burning markers. The general existence of nitric acid in oxalic acid-containing particles indicates an acidic environment during the formation process of oxalic acid. Organosulfate-containing particles well correlated with oxalic acid-containing particles during the episode, which suggests the formation of oxalic acid is closely associated with acid-catalyzed reactions of organic precursors.
Cheng, C., Li, M., Chan, C. K., Tong, H., Chen, C., Chen, D., Wu, D., Li, L., Cheng, P., Gao, W., Huang, Z., Li, X., Fu, Z., Bi, Y., and Zhou, Z.: Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implication for seasonal formation mechanism of Secondary Organic Aerosol (SOA), Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1081, in review, 2016.