Seasonal Variations and Sources of Carboxylic Acids in PM2.5 in Wuhan, China

Haotian Guo,Ying Zhou,Jiabin Zhou,Lei Wang,Jinpeng Yuan,Rusong Zhao

doi:10.4209/aaqr.2014.02.0040

Abstract

ABSTRACTAerosol PM2.5 samples collected from three sites in Wuhan, China, during 2011–2012 were analyzed by gas chromatography-mass spectrometry to better understand the molecular composition and sources of carboxylic acids. The concentrations of total monocarboxylic acids did not show apparent seasonal variations in Wuhan. Palmitic acid and stearic acid were the most abundant species, accounting for 32.4%–62.4% (average 51.8%) of all quantified monocarboxylic acids. Oxalic acid was found as the most dominant dicarboxylic acid, followed by succinic acid at the three sampling sites. The total concentration of dicarboxylic acids displayed obvious seasonal variation, with the highest in summer (1036.7–1546.4 ng/m3) and the lowest in winter (126.8–211.0 ng/m3). Positive matrix factorization (PMF) revealed that coal combustion, traffic-related emissions and biomass burning are the most important contributors to carboxylic acids at industrial site, downtown site and botanical garden, respectively. Plant waxes and secondary photochemical products are also significant sources of carboxylic acids at the three sampling sites.

Highlights

Organic acids, containing monocarboxylic acids, dicarboxylic acids, aromatic acids and hydroxyl acid, have been reported as the dominant constituents of organic matter in the atmosphere
The total concentration of monocarboxylic acids ranged from 56.11–809.01 ng/m3, 42.06–435.84 ng/m3 and 34.25– 371.92 ng/m3 at Industry Site (ID), Downtown Site (DT) and Botanical Garden (BG) sampling site, respectively
These results suggest that primary exhaust emission was an important source of dicarboxylic acids as well as secondary formation

Summary

Introduction

Organic acids, containing monocarboxylic acids, dicarboxylic acids, aromatic acids and hydroxyl acid, have been reported as the dominant constituents of organic matter in the atmosphere. Carboxylic acids have been found in the urban, rural, and marine atmosphere (Kawamura and Ikushima, 1993; Kawamura et al, 1996a; Kerminen et al, 2000; Yao et al, 2002; Huang et al, 2005; Ho et al, 2006). The previous studies demonstrate that carboxylic acids can significantly contribute to the acidity of rainwater in urban and rural environments (Kawamura et al, 1996b). They have potential to alter the hygroscopic property of atmospheric aerosols and to change global radiation balance as well as causing health problems (Facchini et al., 1999; Kerminen, 2001). Possible pathways from some gas-phase and primary precursor to carboxylic acids were proposed but limited (Kawamura et al, 1996b; Yao et al, 2002, 2004)

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Conclusion