Articles | Volume 17, issue 15
Atmos. Chem. Phys., 17, 9519–9533, 2017
Atmos. Chem. Phys., 17, 9519–9533, 2017

Research article 08 Aug 2017

Research article | 08 Aug 2017

Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implications for the formation mechanism of oxalic acid

Chunlei Cheng1,2, Mei Li1,2, Chak K. Chan3, Haijie Tong4, Changhong Chen5, Duohong Chen6, Dui Wu1,2, Lei Li1,2, Cheng Wu1,2, Peng Cheng1,2, Wei Gao1,2, Zhengxu Huang1,2, Xue Li1,2, Zhijuan Zhang1,2, Zhong Fu7, Yanru Bi7, and Zhen Zhou1,2 Chunlei Cheng et al.
  • 1Institute 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

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. The HM particles were the most abundant oxalic acid particles in summer and the diurnal variations in peak area of iron and oxalic acid show opposite trends, which suggests a possible loss of oxalic acid through the photolysis of iron oxalato-complexes during the strong photochemical activity period. In wintertime, carbonaceous particles contained a substantial amount of oxalic acid as well as abundant carbon clusters and BB markers. The general existence of nitric acid in oxalic-acid-containing particles indicates an acidic environment during the formation process of oxalic acid. The peak areas of nitrate, sulfate and oxalic had similar temporal change in the carbonaceous type oxalic acid particles, and the organosulfate-containing oxalic acid particles correlated well with total oxalic acid particles during the haze episode, which suggests that the formation of oxalic acid is closely associated with the oxidation of organic precursors in the aqueous phase.

Short summary
Oxalic acid is an abundant and ubiquitous constituent in secondary organic aerosol (SOA) and can be an effective tracer for the oxidative processes leading to the formation of SOA. In this work photochemical reactions have a significant contribution to oxalic acid formation in summer, while in winter the formation of oxalic acid is closely associated with the oxidation of organic precursors in the aqueous phase.
Final-revised paper