Molecular Distribution and Stable Carbon Isotopic Composition of Dicarboxylic Acids, Ketocarboxylic Acids, and α-Dicarbonyls in Size-Resolved Atmospheric Particles From Xi’an City, China

Abstract

Size-resolved airborne particles (9-stages) in urban Xi'an, China, during summer and winter were measured for molecular distributions and stable carbon isotopic compositions of dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls. To our best knowledge, we report for the first time the size-resolved differences in stable carbon isotopic compositions of diacids and related compounds in continental organic aerosols. High ambient concentrations of terephthalic (tPh, 379 ± 200 ng m(-3)) and glyoxylic acids (ωC(2), 235 ± 134 ng m(-3)) in Xi'an aerosols during winter compared to those in other Chinese cities suggest significant emissions from plastic waste burning and coal combustions. Most of the target compounds are enriched in the fine mode (<2.1 μm) in both seasons peaking at 0.7-2.1 μm. However, summertime concentrations of malonic (C(3)), succinic (C(4)), azelaic (C(9)), phthalic (Ph), pyruvic (Pyr), 4-oxobutanoic (ωC(4)), and 9-oxononanoic (ωC(9)) acids, and glyoxal (Gly) in the coarse mode (>2.1 μm) are comparable to and even higher than those in the fine mode (<2.1 μm). Stable carbon isotopic compositions of the major organics are higher in winter than in summer, except oxalic acid (C(2)), ωC(4), and Ph. δ(13)C of C(2) showed a clear difference in sizes during summer, with higher values in fine mode (ranging from -22.8‰ to -21.9‰) and lower values in coarse mode (-27.1‰ to -23.6‰). The lower δ(13)C of C(2) in coarse particles indicate that coarse mode of the compound originates from evaporation from fine mode and subsequent condensation/adsorption onto pre-existing coarse particles. Positive linear correlations of C(2), sulfate and ωC(2) and their δ(13)C values suggest that ωC(2) is a key intermediate, which is formed in aqueous-phase via photooxidation of precursors (e.g., Gly and Pyr), followed by a further oxidation to produce C(2).

Compositions and sources of organic acids in fine particles (PM2.5) over the Pearl River Delta region, south China

“…However, our study instead revealed higher 1,4-phthalic acid in average (28.2 ng/m 3 ) than 1,2-phthalic acid (23.9 ng/m 3 ), the same as those reported in the polluted city sites, such as Chennai in India and Xi'an in China (Fu et al, 2010;Wang et al, 2012a). The levels of 1,4-phthalic acid and 1,2-phthalic acid quite approximated those reported in China and India, but were higher than those reported in USA.…”

“…In this study, 1,4-phthalic acid was found to be significantly correlated with 1,3,5-triphenylebenzene (r = 0.70, p < 0.01), which is a specific marker for the open-burning of plastics (Simoneit et al, 2005). This source of 1,4-phthalic acid can largely explain its higher levels in many Asian cities (Fu et al, 2010;Ho et al, 2010;Wang et al, 2012a) and its rare occurrence in aerosols from oceans and the Arctic (Narukawa et al, 2002;Simoneit et al, 2004). The quite different spatial patterns of 1,4-phthalic acid comparing to the secondarily formed 1,2-phthalic acid, as well as significant correlation between 1,4-phthalic acid and EC (r = 0.59, p < 0.01; Table 2), also supports that 1,4-phthalic acid was a primary pollutant.…”

“…fatty acids), are important atmospheric oxygenated organic aerosols in PM 2.5 Wang et al, 2006). These acids are either directly emitted from various natural and anthropogenic sources (Ho et al, 2010;Oliveira et al, 2007) or secondarily formed from oxidation of gas-phase precursors followed by gas/particle partition (Wang et al, 2012a). Organic acids are involved in a series of atmospheric chemical reactions occurring in the gas, water and particle phases (Chebbi and Carlier, 1996); they can reduce the surface tension of particles to form cloud condensation nuclei (Facchini et al, 1999), and laboratory experiments also indicate that nucleation of sulfuric acid is considerably enhanced in the presence of organic acids like aromatic acids .…”

Impact of Gobi desert dust on aerosol chemistry of Xi'an, inland China during spring 2009: differences in composition and size distribution between the urban ground surface and the mountain atmosphere

“…WSOC in the urban atmospheric presented a predominance in the fine mode with a small peak in the coarse mode during the nonevent, in contrast to a unimodal pattern of WSIC, which is dominant in the coarse mode ( Fig. 9a-d from photochemical oxidation of organic gases (Agarwal et al, 2010;Ram and Sarin, 2010;Salma et al, 2007;Wang et al, 2012a;Yu et al, 2004Yu et al, , 2005. Moreover, biomass burning is also an important source of WSOC.…”

“…In each spring and early summer surface dust in Gobi desert region is brought about by front cold systems and the Mongolian cyclonic depression and transported into the downwind areas including North America (Leaitch et al, 2009;Seinfeld et al, 2004;VanCuren and Cahill, 2002). During transport mineral dust can internally mix with secondary compounds such as ammonium sulfate, ammonium nitrate, carboxylic acids, nitrogen-containing organics and sea salt by coagulation, cloud-processing and heterogeneous reactions (Geng et al, 2009;Seinfeld et al, 2004;Sullivan et al, 2009a;Tobo et al, 2010;Wang et al, 2012a;Zamora et al, 2011;. These processes modify the physicochemical properties of the airborne aerosols containing dust, exerting a significant impact on the downwind atmospheric environment (Dillner et al, 2006).…”