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

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 (&delta;¹⁵N) composition of aerosol total nitrogen, which ranged from 18.1 to 25.4&permil;, 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 (<i>r</i>² = 0.95). In addition, WSOC to OC (or TC) ratios remain almost constant for daytime (0.37 &pm; 0.06 (0.28 &pm; 0.04)) and nighttime (0.38 &pm; 0.07 (0.28 &pm; 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 (<i>r</i>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;¹³C) of TC ranged from −27.0 to −25.4&permil;, with slightly lower average (−26.5 &pm; 0.3&permil;) in summer than in winter (−25.9 &pm; 0.3&permil;). Positive correlation between WSOC/TC ratios and &delta;¹³C 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 (<i>n</i>=25) and more information on this topic may be needed from other similar coastal sites in future

Carbon isotope‐constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo‐Gangetic Plain

“…One therefore expects a higher 13 C enrichment of OC in the water‐soluble phase (WSOC), which we have observed at several sites with increasing effects as a function of distance from the source [ Bosch et al ., ; Kirillova et al ., ; Kirillova et al ., ; Kirillova et al ., ]. These findings in ambient settings are also corroborated by laboratory studies and compound‐specific investigations of δ 13 C of the effects of aging [ Aggarwal et al ., ; Aggarwal and Kawamura , ; Pavuluri and Kawamura , ; Wang and Kawamura , ].…”

“…This observation highlights the relative significance of TC from local emissions in summer (cluster 3) compared with those derived from long‐range transport of mixed air masses, which are influenced by both dust and biomass combustion sources. However, the CWT‐derived δ 13 C signature shows no such variability for all three clusters, presumably due to overlapping δ 13 C TC signatures from vehicular emissions (−26.4 ± 0.3‰ [ Agnihotri et al ., ] and −26.4 ± 0.4‰ [ Aggarwal et al ., ]) and biomass combustion sources (C 3 vegetation from Amazon, −26.9‰ to −24.9‰ [ Martinelli et al ., ]; domestic wood fuel, −28 to −25‰ [ Agnihotri et al ., ]; Mt. Tai, China, −26.6 to −23.2 ‰ [ Fu et al ., ]; Indonesian forest fires, −25.5‰ to −27.5‰ [ Narukawa et al ., ]; and Southeast Asian fires, −26.9 to −24.2‰ [ Bikkina et al ., ]).…”

“…It is also worthwhile to mention that source‐specific stable carbon isotopic composition of TC from FF‐comb source used in this study is not from the IGP, which therefore introduces some uncertainty. However, source‐specific δ 13 C of FF‐comb from South Asia [ Aggarwal et al ., ; Agnihotri et al ., ; Agnihotri et al ., ] is consistent with the literature data [ Cao et al ., ; Ho et al ., ; Widory , ] and, therefore, may not bias the results in this study.…”

Characterization of water-soluble organic matter in urban aerosol by 1H-NMR spectroscopy

“…The lowest δ 13 C ratio values may also be indicative of SOA formation through the oxidation of volatile organic compounds. However, atmospheric aging processes result in δ 13 C ratio increase (Aggarwal et al, 2013). …”

Seasonal and longitudinal distributions of atmospheric water‐soluble dicarboxylic acids, oxocarboxylic acids, and α‐dicarbonyls over the North Pacific

“…The water‐soluble dicarboxylic acids, oxocarboxylic acids, and α ‐dicarbonyls are some of the most extensively studied OA components over the continents [ Agarwal et al ., ; Aggarwal et al ., ; Ho et al ., ; Kawamura and Yasui , ; Miyazaki et al ., ; Pavuluri et al ., ; Wang et al ., ]. However, the studies on their chemical characterization over the open oceanic regions are mostly for the latitudinal distributions, and the studies on longitudinal distributions are very limited [ Bikkina et al ., , ; Fu et al ., ; Kawamura et al ., ; Kawamura and Sakaguchi , ; Kawamura and Usukura , ; Kunwar and Kawamura , ; Sempéré and Kawamura , ].…”