Water‐soluble organic carbon and oxalate in aerosols at a coastal urban site in China: Size distribution characteristics, sources, and formation mechanisms

Abstract

[1] Water-soluble organic compounds in aerosol contribute a significant fraction to organic aerosol mass and influence interactions of aerosols with water in the atmosphere. Despite their importance, the sources and formation mechanisms of these compounds are not well understood. In this work, we measured the size distributions of watersoluble organic carbon (WSOC) and its most abundant single component, oxalate, in the urban area of Shenzhen, a coastal metropolitan city in southern China. In the cloud condensation nuclei size range, organic compounds were found to constitute a significant fraction (roughly one half) of the total water-soluble substance mass. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, with their respective modal peak at 0.4, 1.0, and 5.5 mm. Both WSOC and oxalate had a dominant droplet mode, a minor condensation mode, and a minor coarse mode. Approximately one half of WSOC and two thirds of oxalate mass were in the droplet mode. The sources and formation mechanisms of oxalate and WSOC were inferred in reference to the well-understood size distribution characteristics of inorganic species (Ca 2+ , Na + , K + , and SO 4 2À ), in conjunction with source identification and contribution estimation by PMF. We found that the droplet mode oxalate was mostly produced from in-cloud aqueous phase reactions. Among significant sources contributing to the total WSOC were biomass burning, in-cloud processing, soil dust particles, and aged sea salt particles. The first two sources were the major contributors to the droplet WSOC, while the latter two were responsible for the coarse mode WSOC. The droplet mode WSOC correlated well with K + and sulfate, consistent with the source estimates by PMF. Future work on WSOC is suggested to be directed at characterizing the biomass burning aerosols and elucidating the molecular formation pathways in the aqueous phase.

Exploration of PM<sub>2.5</sub> sources on the regional scale in the Pearl River Delta based on ME-2 modeling

“…The average concentration of secondary nitrate during northerly flow in winter was 40 times greater than that during southerly flow in summer; this occurred not only because of the unfavorable conditions of atmospheric diffusion in winter but also due to the high semi-volatility of ammonium nitrate, which cannot stably exist in fine particles in the PRD during hot summer weather (Huang et al, 2006). Under southerly flow conditions, the concentrations of secondary nitrate presented prominent differences among the six sites, showing local characteristics.…”

“…Therefore, these high-abundance species were not constrained in the sea salt and fugitive dust factors, while the other species (with abundances of less than 0.1 % in the particulates) were constrained to zero (Table 4). In addition, HNO 3 might react with sea salt to displace Cl − (Huang et al, 2006); thus, NO − 3 was also not constrained in the sea salt factor.…”

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

“…Although a number of studies have focused on chemical characteristics and sources of WSOC (Cheng et al, 2012;Huang et al, 2006;Miyazaki et al, 2007;Park et al, 2015), studies about the artifacts of WSOC during sampling, thermal characteristics of WSOC and its application to source appointment were limited. In our study, we developed a method to obtain the temperature-resolved carbon fractions of WSOC.…”

Source and formation characteristics of water-soluble organic carbon in the anthropogenic-influenced Yellow River Delta, North China

“…For example, a well study investigated the organic carbon precipitation elaborately and showed total carbon deposition flux could be up to 3.2 g C m À2 yr À1 in North China, greatly affecting the ecosystem (Pan et al, 2010). Considering the critical role of WSOC in the aerosol pollution, a certain amount of researches about its source and formation have been carried out by various methods, such as PMF modeling and traces (Du et al, 2014;Huang et al, 2006), in this region. However, significant difference was found from previous assessments mainly due to the particularly complicated source of WSOC (Pan et al, 2010).…”

“…Because of its affinity with water, WSOC is absolutely responsible for altering the aerosol hygroscopicity, determining the particles acting as cloud condensation nuclei (CCN), and even for the formation of haze (Haque et al, 2016;Huang et al, 2006;Saffari et al, 2016;Sun et al, 2016;Wu et al, 2016). Generally, WSOC can be either directly emitted or formed in the atmosphere via the oxidation of the anthropogenic and biogenic volatile organic compounds (VOCs) (Kumagai et al, 2009).…”