14 Sep 2022
14 Sep 2022
Status: this preprint is currently under review for the journal ACP.

Biogenic and anthropogenic sources of isoprene and monoterpenes and their secondary organic aerosol in Delhi, India

Daniel J. Bryant1, Beth S. Nelson1, Stefan J. Swift1,a, Sri Hapsari Budisulistiorini1, Will S. Drysdale1,2, Adam R. Vaughan1, Mike J. Newland1,b, James R. Hopkins1,2, James M. Cash3,4, Ben Langford3, Eiko Nemitz3, W. Joe F. Acton5,c, C. Nicholas Hewitt5, Tuhin Mandal6, Bhola R. Gurjar6, Shivani6,d, Ranu Gadi6, James D. Lee1,2, Andrew R. Rickard1,2, and Jacqueline F. Hamilton1 Daniel J. Bryant et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
  • 2National Centre for Atmospheric Science, University of York, Heslington, York, YO10 5DD, UK
  • 3UK Centre for Ecology and Hydrology, Penicuik, Midlothian, Edinburgh, EH26 0QB, UK
  • 4School of Chemistry, University of Edinburgh, Edinburgh, EH9 3FJ, Edinburgh, UK
  • 5Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YW, UK
  • 6Department of Applied Sciences and Humanities, Indira Gandhi Delhi Technical University for Women, Delhi, 110006, India
  • anow at: J. Heyrovsky Institute of Physical Chemistry, Department of Chemistry of Ions in Gaseous Phase, Prague, Czech Republic
  • bnow at: ICARE-CNRS, 1 C Av. de la Recherche Scientifique, 45071 Orléans CEDEX 2, France
  • cnow at: School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK
  • dnow at: Department of Chemistry, Miranda House, Delhi University, Delhi, 110007, India

Abstract. Isoprene and monoterpenes emissions to the atmosphere are generally dominated by biogenic sources. The oxidation of these compounds can lead to the production of secondary organic aerosol, however the impact of this chemistry in polluted urban settings has been poorly studied. Isoprene and monoterpenes can form SOA heterogeneously via anthropogenic-biogenic interactions resulting in the formation of organosulfates (OS) and nitrooxy-organosulfates (NOS). Delhi, India is one of the most polluted cities in the world, but little is known about the emissions of biogenic VOCs or the sources of SOA. As part of the DELHI-FLUX project, gas phase mixing ratios of isoprene and speciated monoterpenes were measured during pre- and post-monsoon measurement campaigns in central Delhi. Nocturnal mixing ratios of the VOCs were substantially higher during the post-monsoon (isoprene: (0.65 ± 0.43) ppbv, limonene: (0.59 ± 0.11) ppbv, α-pinene: (0.13 ± 0.12) ppbv) than the pre-monsoon (isoprene: (0.13 ± 0.18) ppbv, limonene: 0.011 ± 0.025 (ppbv), α-pinene: 0.033 ± 0.009) period. At night, isoprene and monoterpene concentrations correlated strongly with CO across during the post-monsoon period. This is one of the first observations in Asia, suggesting monoterpene emissions are dominated by anthropogenic sources. Filter samples of particulate matter less than 2.5 microns in diameter (PM2.5) were collected and the OS and NOS content analysed using ultrahigh-performance liquid chromatography tandem mass spectrometry (UHPLC-MS2). Inorganic sulfate was shown to facilitate the formation of isoprene OS species across both campaigns. Sulfate contained within OS and NOS species were shown to contribute significantly to the sulfate signal measured via AMS. Strong nocturnal enhancements of NOS species were observed across both campaigns. The total concentration of OS/NOS species contributed an average of (2.0 ± 0.9) % and (1.8 ± 1.4) % to the total oxidised organic aerosol, and up to a maximum of 4.2 % and 6.6 % across the pre- and post-monsoon periods, respectively. Overall, this study provides the first molecular level measurements of SOA derived from isoprene and monoterpene in Delhi and demonstrates that both biogenic and anthropogenic sources of these compounds can be important in urban areas.

Daniel J. Bryant et al.

Status: open (until 26 Oct 2022)

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Daniel J. Bryant et al.

Daniel J. Bryant et al.


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Short summary
This paper investigates the sources of isoprene and monoterpene compounds and their particulate phase oxidation products in Delhi, India. This was done to improve our understanding of the sources, concentrations, and fate of volatile emissions in megacities. By studying the chemical composition of offline filter samples, we report a significant share of the oxidised organic aerosol in Delhi is from isoprene and monoterpenes. This has implications for human health and policy development.