Seasonal Analysis of Submicron Aerosol in Old Delhi Using High
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Atmos. Chem. Phys., 21, 10133–10158, 2021 https://doi.org/10.5194/acp-21-10133-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. 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 J. Mullinger1, James Allan3, Ernesto Reyes-Villegas3, Ruthambara Joshi3, Mathew R. Heal2, W. Joe F. Acton4,a, C. Nicholas Hewitt4, Pawel K. Misztal1,b, Will Drysdale5, Tuhin K. Mandal6, Shivani7, Ranu Gadi7, Bhola Ram Gurjar8, and Eiko Nemitz1 1UK Centre for Ecology & Hydrology, Edinburgh Research Station, Penicuik, EH26 0QB, UK 2School of Chemistry, University of Edinburgh, Edinburgh, Edinburgh, EH9 3FJ, 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 6Council of Scientific and Industrial Research–National Physical Laboratory (CSIR-NPL), New Delhi, 110012, India 7Department of Applied Sciences and Humanities, Indira Gandhi Delhi Technical University for Women, Delhi, 110006, India 8Department of Civil Engineering, Indian Institute of Technology Roorkee, 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 Correspondence: James Cash ([email protected]) and Eiko Nemitz ([email protected]) Received: 6 October 2020 – Discussion started: 23 October 2020 Revised: 10 May 2021 – Accepted: 10 May 2021 – Published: 7 July 2021 Abstract. We present the first real-time composition of sub- origin to crop residue burning. The second is a solid fuel micron particulate matter (PM1) in Old Delhi using high- OA (SFOA) factor with links to local open burning due to resolution aerosol mass spectrometry (HR-AMS). Old Delhi its high composition of polyaromatic hydrocarbons (PAHs) is one of the most polluted locations in the world, and PM1 and novel AMS-measured marker species for polychlori- concentrations reached ∼ 750 µg m−3 during the most pol- nated dibenzodioxins (PCDDs) and polychlorinated diben- luted period, the post-monsoon period, where PM1 increased zofurans (PCDFs). Two traffic factors were resolved: one by 188 % over the pre-monsoon period. Sulfate contributes hydrocarbon-like OA (HOA) factor and another nitrogen- the largest inorganic PM1 mass fraction during the pre- rich HOA (NHOA) factor. The N compounds within NHOA monsoon (24 %) and monsoon (24 %) periods, with nitrate were mainly nitrile species which have not previously been contributing most during the post-monsoon period (8 %). The identified within AMS measurements. Their PAH composi- organics dominate the mass fraction (54 %–68 %) through- tion suggests that NHOA is linked to diesel and HOA to com- out the three periods, and, using positive matrix factorisa- pressed natural gas and petrol. These factors combined make tion (PMF) to perform source apportionment analysis of or- the largest relative contribution to primary PM1 mass during ganic mass, two burning-related factors were found to con- the pre-monsoon and monsoon periods while contributing tribute the most (35 %) to the post-monsoon increase. The the second highest in the post-monsoon period. A cooking first PMF factor, semi-volatility biomass burning organic OA (COA) factor shows strong links to the secondary factor, aerosol (SVBBOA), shows a high correlation with Earth ob- semi-volatility oxygenated OA (SVOOA). Correlations with servation fire counts in surrounding states, which links its co-located volatile organic compound (VOC) measurements Published by Copernicus Publications on behalf of the European Geosciences Union. 10134 J. M. Cash et al.: Seasonal analysis of submicron aerosol in Old Delhi and AMS-measured organic nitrogen oxides (OrgNO) sug- out these studies there are multiple versions of the same gest SVOOA is formed from aged COA. It is also found that a source, and this requires additional auxiliary measurements significant increase in chloride concentrations (522 %) from to pin down their origin. This study aims to better assign fac- pre-monsoon to post-monsoon correlates well with SVB- tors to their original sources using additional measurements BOA and SFOA, suggesting that crop residue burning and of volatile organic compounds (VOCs), black carbon (BC), open waste burning are responsible. A reduction in traf- carbon monoxide (CO), nitrogen oxides (NOx/ and Earth ob- fic emissions would effectively reduce concentrations across servations. most of the year. In order to reduce the post-monsoon peak, A growing number of studies in Delhi, and other locations sources such as funeral pyres, solid waste burning and crop in India, have reported large concentrations of chloride, es- residue burning should be considered when developing new pecially during the morning hours at ∼ 07:00–09:00 (Sud- air quality policy. heer et al., 2014; Chakraborty et al., 2018; Gani et al., 2019; Acharja et al., 2020; Reyes-Villegas et al., 2020; Tobler et al., 2020; Lalchandani et al., 2021). The source of this chlo- ride is still widely debated, and there are several possibil- 1 Introduction ities, including aluminium pickling, industrial activity, mu- nicipal waste burning and biomass burning. The aluminium The number of premature deaths linked to fine particulate pickling industry in the north-west of Delhi is thought to matter (PM2:5) globally was estimated at 4.1 million in directly emit HCl and be the main contributor to chloride 2016, and 10.6 % were in India alone (Gakidou et al., during the winter months when average concentrations in- 2017). Some of the most polluted cities in the world crease from 1.5 µg m−3 in the summer to 23 µg m−3 in the are in India, with Delhi being in the top 10 cities listed winter (Gani et al., 2019). Studies in Mexico City suggest a by the World Health Organization based on available substantial amount of chloride is from biomass and munici- annual PM2:5 measurements in 2018 (World Health Or- pal waste burning, and they also observe high concentrations ganization, https://www.who.int/data/gho/data/themes/ from crop residue burning (Christian et al., 2010; Li et al., topics/topic-details/GHO/ambient-air-pollution, last access: 2012). In Delhi, these sources may also be high contribu- 20 April 2021). This has a significant effect on the health tors as it would explain why chloride concentrations show a of its population (26 million), and in 2016 it was estimated larger elevation during the colder post-monsoon and winter that fine particulate matter (PM2:5) accounted for ∼ 15 000 months than other compounds. premature deaths per year (Maji et al., 2018). Therefore, it During the post-monsoon period, large-scale crop residue is important to investigate the sources of PM to improve air burning occurs along with large numbers of Delhi residents quality mitigation strategies. burning municipal waste to keep warm and clean streets. The composition of submicron PM (PM1) is a mixture These open burning sources produce chloride in different of organic aerosol (OA), black carbon (BC) and inorganic organic and inorganic forms. Inorganic NH4Cl is related to aerosols including ammonium, sulfate, chloride and nitrate. biomass burning through the release of particulate KCl that The high-resolution aerosol mass spectrometer (HR-AMS) forms HCl and ultimately NH4Cl once reacted with ammonia has helped to improve measurements of PM1 as it gives (Sullivan et al., 2007; Wang et al., 2017). Emissions of HCl detailed information on its chemical composition through are often associated with plastic burning, but there are also elemental analysis and high-resolution compound identifi- organic species of chloride, such as polychlorinated diben- cation. Combining these measurements with positive ma- zofurans (PCDFs) and dibenzodioxins (PCDDs), that form trix factorisation (PMF) allows for the apportionment of readily from chloride-rich plastics such as polyvinyl chlo- aerosol mass into different sources (or factors). This pro- ride (PVC) and polychlorinated biphenyls (PCBs) (Minh et vides detailed information needed to inform effective air al., 2003; Chakraborty et al., 2013; Stewart et al., 2021). quality interventions. To date, relatively few measurements Large-scale plastic burning practises in Delhi, such as elec- of PM composition have been made by HR-AMS in In- tronic waste recycling centres situated in the north-west, dia, with measurements made in Kanpur a notable excep- could therefore be high contributors to chloride mass. The tion (Chakraborty et al., 2015, 2016a, b, 2018). These HR- measurement of plastic burning markers is therefore impor- AMS measurements however give multiple factor solutions, tant to understand the contribution of such practises to chlo- often of six or greater, which highlights the complexity ride concentrations. of the source mix. Typical sources identified include com- This study focuses on the high-resolution aspect of ponents considered to be primary, such as hydrocarbon- the high-resolution time-of-flight aerosol mass spectrometer like organic aerosol (HOA) and biomass burning organic (HR-TOF-AMS) and investigates the detailed composition of aerosol (BBOA), as well as components usually