Abstract
Abstract. Thirty water-soluble organic species, including dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls, fatty acids and benzoic acid were determined as well as organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) in PM2.5 samples collected during the Campaign of Air Quality Research in Beijing 2007 (CAREBeijing-2007) in the urban and suburban areas of Beijing. The objective of this study is to identify the influence of traffic emissions and regional transport to the atmosphere in Beijing during summer. PM2.5 samples collected with or without traffic restriction in Beijing are selected to evaluate the effectiveness of local traffic restriction measures on air pollution reduction. The average concentrations of the total quantified bifunctional organic compounds (TQBOCs), total fatty acids and benzoic acid during the entire sampling period were 1184±241, 597±159 and 1496±511 ng m−3 in Peking University (PKU), and 1050±303, 475±114 and 1278±372 ng m−3 in Yufa, Beijing. Oxalic acid (C2) was found as the most abundant dicarboxylic acid at PKU and Yufa followed by phthalic acid (Ph). A strong even carbon number predominance with the highest level at stearic acid (C18:0), followed by palmitic acid (C16:0) was found for fatty acids. According to the back trajectories modeling results, the air masses were found to originate mainly from the northeast, passing over the southeast or south of Beijing (heavily populated, urbanized and industrialized areas), during heavier pollution events, whereas they are mainly from the north or northwest sector (mountain areas without serious anthropogenic pollution sources) during less pollution events. The data with wind only from the same sector (minimizing the difference from regional contribution) but with and without traffic restriction in Beijing were analyzed to evaluate the effectiveness of local traffic restriction measures on the reduction of local air pollution in Beijing. The results suggested that the traffic restriction measures can reduce the air pollutants, but the decrease of pollutants is generally smaller in Yufa compared to that in PKU. Moreover, an enhancement of EC value indicates more elevated primary emissions in Yufa during restriction periods than in non-restriction periods. This study demonstrates that even when primary exhaust was controlled by traffic restriction, the contribution of secondary organic species formed from photochemical processes was critical with long-range atmospheric transport of pollutants.
Highlights
Organic aerosol (OA) typically constitutes 20–90 % of submicron aerosol (Huang et al, 2014; Jimenez et al, 2009) and is influencing Earth’s climate directly by absorbing and scattering radiation and indirectly by acting as cloud condensation
It was consistent with the water-soluble organic carbon (WSOC) / organic carbon (OC) ratios (20–40 %) at other metropolitan cities (Ho et al, 2007; Yang et al, 2005), suggesting that WSOC is one of the main components in OA in China
During the CAREBeijing-2007 in summer, molecular compositions of bifunctional organic compounds, fatty acids and benzoic acid were studied in Beijing
Summary
Organic aerosol (OA) typically constitutes 20–90 % of submicron aerosol (Huang et al, 2014; Jimenez et al, 2009) and is influencing Earth’s climate directly by absorbing and scattering radiation and indirectly by acting as cloud condensation. Despite the dominant presence of water-soluble organic carbon (WSOC) in the atmosphere, there exist large uncertainties associated with sources, the chemical composition, removal mechanisms and atmospheric formation processing of aerosol WSOC. This is evident in polluted megacities where multiple sources of local and regional origins may significantly change the chemical and physical properties of aerosol and influence air quality, climate and human health. Dicarboxylic acids (diacids) are the most abundant organic compounds in OA, which can be derived from primary emissions and/or secondary formation from different precursor species via photochemical reactions (Glasius et al, 2000; Kawamura et al, 1996; Kundu et al, 2010; Legrand et al, 2007). Fossil fuel combustion and biomass burning (Falkovich et al, 2005; Ho et al, 2006; Huang et al, 2014; Kundu et al, 2010) are the major primary sources, whereas photochemical oxidation of volatile organic compounds (VOCs) from biogenic and anthropogenic emissions (Kawamura et al, 1996; Mkoma and Kawamura, 2013) is the major secondary sources
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