23 Oct 2020

23 Oct 2020

Review status: this preprint is currently under review for the journal ACP.

Seasonal analysis of submicron aerosol in Old Delhi using high resolution aerosol mass spectrometry: Chemical characterisation, source apportionment and new marker identification

James M. Cash1,2, Ben Langford1, Chiara Di Marco1, Neil Mullinger1, James Allan3, Ernesto Reyes-Villegas3, Ruthambara Joshi3, Mathew R. Heal2, W. Joe F. Acton4,a, Nick Hewitt4, Pawel Misztal1,b, Will Drysdale5, Tuhin K. Mandal6, Shivani7, Ranu Gadi7, and Eiko Nemitz1 James M. Cash et al.
  • 1UK Centre for Ecology & Hydrology, Edinburgh Research Station, Penicuik, EH26 0QB, UK
  • 2School of Chemistry, University of Edinburgh, Edinburgh, EH9 3FJ, Edinburgh, UK
  • 3Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
  • 4Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
  • 5Wolfson Atmospheric Chemistry Laboratory, University of York, York, YO10 5DD, UK
  • 6CSIR National Physics Laboratory
  • 7Department of Applied Sciences and Humanities, Indira Gandhi Delhi Technical University for Women, Delhi, 110006, India
  • anow at: School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
  • bnow at: Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, Austin, TX 78712, USA

Abstract. We present the first real-time composition of submicron particulate matter (PM1) in Old Delhi using high resolution aerosol mass spectrometry (HR-AMS). Old Delhi is one of the most polluted locations in the world, and PM1 concentrations reached ~ 600 µg m−3 during the most polluted period, the post-monsoon, where PM1 increased by 178 % over the pre-monsoon period. Using positive matrix factorisation (PMF) to perform source apportionment analysis, two burning-related factors contribute the most (35 %) to the post-monsoon increase. The first PMF factor, semi-volatility biomass burning organic aerosol (SVBBOA), shows a high correlation with earth observation fire counts in surrounding states which links its origin to crop residue burning. The second is a solid-fuel OA (SFOA) factor with links to local open burning due to its high composition of polyaromatic hydrocarbons (PAH) and novel AMS measured marker species for polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Two traffic factors were resolved, one hydrocarbon-like OA (HOA) factor and another nitrogen-rich HOA (NHOA) factor. The N compounds within NHOA were mainly nitrile species which have not previously been identified within AMS measurements. Their PAH composition suggests that NHOA is linked to diesel, and HOA to compressed natural gas and gasoline. These factors combined make the largest relative contribution to primary PM1 mass during the pre-monsoon and monsoon periods, while contributing the second highest in the post-monsoon. A cooking OA (COA) factor shows strong links to the secondary factor, semi-volatility oxygenated OA (SVOOA). Correlations with co-located volatile organic compound (VOC) measurements and AMS measured organic nitrogen oxides (OrgNO) suggest SVOOA is formed from aged COA. It is also found that a significant increase in chloride concentrations (488 %) from pre-monsoon to post-monsoon correlates well with SVBBOA and SFOA suggesting that crop residue burning and open waste burning are responsible. A reduction in traffic emissions would effectively reduce concentrations across most of the year. In order to reduce the post-monsoon peak, sources such as funeral pyres, solid waste burning and crop residue burning should be considered when developing new air quality policy.

James M. Cash et al.

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Status: final response (author comments only)
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James M. Cash et al.

James M. Cash et al.


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Short summary
We present the first real-time composition of submicron particulate matter (PM1) in Old Delhi using high resolution aerosol mass spectrometry. Seasonal analysis shows peak concentrations occur during the post-monsoon and novel-tracers reveal the largest sources are a combination of local open and regional crop residue burning. Strong links between increased chloride aerosol concentrations and burning sources of PM1 suggest burning sources are responsible for the post-monsoon chloride peak.