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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 20 Jan 2020

Submitted as: research article | 20 Jan 2020

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This preprint is currently under review for the journal ACP.

Non methane hydrocarbon (NMHC) fingerprints of major urban and agricultural emission sources active in South Asia for use in source apportionment studies

Ashish Kumar1, Vinayak Sinha1, Muhammed Shabin1, Haseeb Hakkim1, Bernard Bonsang2, and Valerie Gros2 Ashish Kumar et al.
  • 1Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S.A.S Nagar, Manauli PO, Punjab, 140306, India
  • 2LSCE, Laboratoire des Sciences du Climat et de l'Environnement, CNRS-CEA-UVSQ, IPSL, Université Paris Saclay, Orme des Merisiers, F91191 Gif-sur-Yvette, France

Abstract. In complex atmospheric emission environments such as urban agglomerates, multiple sources control the ambient chemical composition driving air quality and regional climate. In contrast to pristine sites, where reliance on single or few chemical tracers is often adequate to resolve pollution plumes and source influences, comprehensive chemical fingerprinting of sources using non-methane hydrocarbons and identification of suitable tracer molecule/molecules and emission ratios is necessary. Here, we characterize and present chemical fingerprints of some major urban and agricultural emission sources active in South Asia such as paddy stubble burning, garbage burning, idling vehicular exhaust and evaporative fuel emissions. Whole air samples were collected actively from the emission sources in passivated air sampling steel canisters and then analyzed for 49 NMHCs (22 alkanes, 16 aromatics, 10 alkene and 1 alkyne) using thermal desorption gas chromatography flame ionisation detection (TD-GC-FID). Based on the measured source profiles, chemical tracers were identified for distinguishing varied emission sources and also for use in PMF source apportionment models. Thus, we were able to identify chemical tracers such as i-pentane for petrol vehicular exhaust and evaporative emissions, propane for LPG evaporative and LPG vehicular exhaust emissions, and acetylene for the biomass fires during the flaming stage. Furthermore, we observed propane to be a major NMHC emission (8 %) from paddy stubble fires and therefore in an emission environment impacted by crop residue fires, use of propane as a fugitive LPG emission tracer requires caution. Isoprene was identified as a potential tracer for distinguishing paddy stubble and garbage burning in the absence of isoprene emissions at night from biogenic sources. Diesel vehicular exhaust comprised of > 50 % alkenes and alkyne by mass composition while diesel evaporative emissions were enriched in C5–C8 alkanes and aromatics. The secondary pollutant formation potential and human health impact of the sources was also assessed in terms of their OH reactivity (s−1), ozone formation potential (OFP, gO3/gNMHC) and fractional BTEX content. Petrol vehicular exhaust emissions, paddy stubble fires and garbage fires were identified as the most polluting among the sources studied in this work. Source specific inter-NMHC molar ratios which are often employed for identifying ambient air pollution emission plumes and assessing photochemical ageing were also examined. Toluene / benzene (T / B) ratios were a good tracer for distinguishing the paddy stubble fire emissions in flaming (0.42) and smoldering stages (1.39), garbage burning emissions (0.21–0.32) and traffic emissions (3.54). While i-butane / n-butane ratios were found to be similar (0.20–0.30) for many sources, i-pentane / n-pentane ratios were useful for distinguishing biomass burning emissions (0.09–0.70) from the traffic/fossil fuel emissions (1.55–8.77). The results of this study provide a new foundational framework for quantitative source apportionment studies in complex emission environments such as South Asia.

Ashish Kumar et al.

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Ashish Kumar et al.

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Publications Copernicus
Short summary
Source apportionment studies require information concerning the chemical fingerprints of pollution sources for correct quantification of source contributions to ambient composition. These chemical fingerprints vary from region to region depending on fuel composition and combustion conditions and are poorly constrained over developing regions such as South Asia. This work characterizes chemical fingerprints of urban and agricultural sources using 49 NMHCs and their impacts on environment.
Source apportionment studies require information concerning the chemical fingerprints of...