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Journal article

Organic and inorganic markers and stable C-, N-isotopic compositions of tropical coastal aerosols from megacity Mumbai: Sources of organic aerosols and atmospheric processing

Aggarwal S, Kawamura K, Umarji G, Tachibana E, Patil R, Gupta P ...see all

Atmospheric Chemistry and Physics, vol. 13, issue 9 (2013) pp. 4667-4680

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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 (C-2), azelaic acid (C-9), and
levoglucosan. The results revealed that biofuel/biomass burning and
fossil fuel combustion are the major sources of the Mumbai aerosols.
Nitrogen-isotopic (delta N-15) 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, C-2
diacid and nssSO(4)(2-), do not show diurnal changes. Concentrations of
C-2 diacid and WSOC show a strong correlation (r(2) = 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 C-9 diacid present a positive
correlation (r(2) = 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 (delta C-13) 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 delta C-13 values suggested that the relative increment in C-13 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.

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Authors

  • S. G. Aggarwal

  • K. Kawamura

  • G. S. Umarji

  • E. Tachibana

  • R. S. Patil

  • P. K. Gupta

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