Abstract
PM10 samples were collected from Huangshi (HS) city, Central China during April 2012 to March 2013, and were analyzed for short-chain saturated dicarboxylic acids (diacids) using a capillary gas chromatograph (GC). We found that oxalic acid (C2, 318 ± 104 ng·m−3) was the most abundant diacid species, followed by malonic acid (C3, 25.4 ± 9.11 ng·m−3) and succinic acid (C4, 2.09 ± 0.52 ng·m−3). The concentrations of C2 and C4 diacids were highest in winter, followed by summer and spring, and lowest in autumn. C3 diacid was decreased in the order of summer > winter > autumn > spring. Further, the seasonal variations of WSOC (water-soluble organic carbon)- and OC (organic carbon)-normalized diacid concentrations were similar to those of diacid concentrations, suggesting that both primary emission and secondary production are important sources for diacids in Huangshi (HS) aerosols. Strong correlations were found among C2 diacid and the three ions SO42−, NO3−, and NH4+ in summer and winter, suggesting that the species could undergo a similar secondary oxidation processing. C2 had good correlation with K+ in summer and autumn, which indicates an enhanced contribution of combustion sources for C2 diacid. Moreover, according to the ratio of C2/K+, we can conclude that C2 diacid should be formed by a secondary reaction of biomass combustion in HS aerosols, especially in summer and autumn. The ratios of C2/C4 and C3/C4 were compared with those reported in other sites, and the results suggest that HS aerosols should be more photochemically aged than at other urban areas. Principal component analysis of diacids and selected water-soluble inorganic ions over four seasons suggests that HS aerosols are influenced not only from primary emission, but also from secondary reaction. According to the linear relation between C2 and C3 diacids, the results indicate that C2 diacid is formed from the oxidation of hydrocarbon compounds in spring, while it is from the oxidation of C3 and C4 diacids in summer, autumn, and winter.
Highlights
Due to their high water-solubility and hygroscopic property, the particles enriched with dicarboxylic acids can act as cloud condensation nuclei (CCN) and perturb the earth’s radiative forcing, and affect regional and global climate [1,2]
We can conclude that C2 diacid should be formed by secondary reaction based on the process of biomass combustion in HS aerosols, especially in summer and autumn
The seasonal variations of diacids and seasonal contributions of diacids to water-soluble organic carbon (WSOC) and organic carbon (OC) suggest that both primary emission and secondary production are important for diacids in the HS aerosols
Summary
Due to their high water-solubility and hygroscopic property, the particles enriched with dicarboxylic acids (diacids) can act as cloud condensation nuclei (CCN) and perturb the earth’s radiative forcing, and affect regional and global climate [1,2]. Diacids can be emitted from various primary sources, such as vehicular exhausts [5], fossil fuel combustion [6], biomass burning [7], cooking activities [8], and natural marine sources [9] They are secondarily formed via atmospheric oxidation of inorganic and organic precursors in the presence of sunlight and oxidants [10,11]. Studies on diacids in atmospheric particles have been conducted in different urban regions of. China, such as the Yangtze River Delta [17,18,19], the Beijing–Tianjin–Hebei region and Guanzhong. We discuss possible sources of organic aerosols and the formation of secondary organic aerosol in HS city
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