Abstract
Abstract. To better understand the sources of PM10 samples in Mumbai, India, aerosol chemical composition, i.e., total carbon (TC), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and inorganic ions were studied together with specific markers such as methanesulfonate (MSA), oxalic acid (C2), azelaic acid (C9), and levoglucosan. The results revealed that biofuel/biomass burning and fossil fuel combustion are the major sources of the Mumbai aerosols. Nitrogen-isotopic (δ15N) composition of aerosol total nitrogen, which ranged from 18.1 to 25.4‰, also suggests that biofuel/biomass burning is a predominate source in both the summer and winter seasons. Aerosol mass concentrations of major species increased 3–4 times in winter compared to summer, indicating enhanced emission from these sources in the winter season. Photochemical production tracers, C2 diacid and nssSO42−, do not show diurnal changes. Concentrations of C2 diacid and WSOC show a strong correlation (r2 = 0.95). In addition, WSOC to OC (or TC) ratios remain almost constant for daytime (0.37 ± 0.06 (0.28 ± 0.04)) and nighttime (0.38 ± 0.07 (0.28 ± 0.06)), suggesting that mixing of fresh secondary organic aerosols is not significant and the Mumbai aerosols are photochemically well processed. Concentrations of MSA and C9 diacid present a positive correlation (r2 = 0.75), indicating a marine influence on Mumbai aerosols in addition to local/regional influence. Backward air mass trajectory analyses further suggested that the Mumbai aerosols are largely influenced by long-range continental and regional transport. Stable C-isotopic ratios (δ13C) of TC ranged from −27.0 to −25.4‰, with slightly lower average (−26.5 ± 0.3‰) in summer than in winter (−25.9 ± 0.3‰). Positive correlation between WSOC/TC ratios and δ13C values suggested that the relative increment in 13C of wintertime TC may be caused by prolonged photochemical processing of organic aerosols in this season. This study suggests that in winter, the tropical aerosols are more aged due to longer residence time in the atmosphere than in summer aerosols. However, these conclusions are based on the analysis of a limited number of samples (n=25) and more information on this topic may be needed from other similar coastal sites in future.
Highlights
Hydrology andAbout half of the world’Es paorptuhlatSioyn sretseidmes in the Indian subcontinent (South Asia) and CShciniae(nEacset Assia), and thesewater-soluble organic carbon (WSOC) to organic carbon (OC) ratios remain almost constant for day- two areas are recognized as potentially important source retime (0.37 ± 0.06 (0.28 ± 0.04)) and nighttime (0.38 ± 0.07 gions for anthropogenic aerosols on a global scale (Lelieveld (0.28 ± 0.06)), suggesting that mixing of fresh secondary or- et al, 2001; Menon et al, 2002; Yamaji et al, 2004).ganic aerosols is not significant and the Mumbai aerosols are photochemically well processed
Yses further suggested that the Mumbai aerosols are largely In South Asia, extensive aerosol characterization studinfluenced by long-range continental and regional transport. ies have been performed duSrinoglitdheEInadiratnhOcean Exper-Stable C-isotopic ratios (δ13C) of total carbon (TC) ranged from −27.0 to iment (INDOEX) in 1999 (Clarke et al, 2002; Lelieveld et al, 2001; Mitra, 2001; Ramanathan et al, 2001)
18 ± 4 32 ± 2 14 ± 2 4.5 ± 1.1 1.4 ± 0.3 3.8 ± 1.7 1.4 ± 0.4 1.4 ± 0.2 a conversion factor to estimate organic matter (OM) mass from OC mass (hereafter, aerosol mass concentration should be regarded as estimated aerosol mass (AM) concentration)
Summary
About half of the world’Es paorptuhlatSioyn sretseidmes in the Indian subcontinent (South Asia) and CShciniae(nEacset Assia), and these. There are two major mechanisms that efficiently lead to SOA formation: (i) the condensation of low-volatility and semivolatile gas compounds on preexisting particles (Mochida et al, 2008; Herner et al, 2006; Robinson et al, 2007; Heald et al, 2010), and (ii) the formation of low-volatility compounds in the aqueous phase (Ervens et al, 2004; Sorooshian et al, 2007; Warneck, 2003) During their lifetime in the atmosphere, particles can get processed, and aerosol characteristics are observed to be altered significantly with time (Zhang et al, 2007). Mass concentrations for aerosol total carbon (TC), elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), and inorganic major ions together with marker compounds and stable C-, N-isotope ratios are presented and discussed in the context of aerosol sources and atmospheric aging in two different seasons. This paper discusses the possible seasonal differences in the lifetime of aerosols in the atmosphere
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