PM<sub>1</sub> composition and source apportionment at two sites in Delhi, India across multiple seasons

Abstract

Abstract. Air pollution in urban environments has been shown to have a negative impact on air quality and human health, particularly in megacities. Over recent decades, Delhi, India has suffered high atmospheric pollution, with significant particulate matter (PM) concentrations as result of anthropogenic activities. Organic aerosols (OA) are composed of thousands of different chemical species and are one of the main constituents of submicron particles. However, quantitative knowledge of OA composition, their sources and processes in urban environments is still limited. This is important particularly in India, as Delhi is a massive, inhomogeneous conurbation, which we would expect that the apportionment and concentrations will vary depending on where in Delhi the measurements/source apportionment is performed, indicating the need of multi-site measurements. This study presents the first multisite analysis carried out in India over different seasons, with a focus on identifying OA sources. The measurements were taken during 2018 at two sites in Delhi, India. One site was located at the India Meteorological Department, New Delhi (ND). The other site was located at the Indira Gandhi Delhi Technical University for Women, Old Delhi (OD). Non-refractory submicron aerosol (NR-PM1) concentrations (ammonium, nitrate, sulphate, chloride and organic aerosols) of four aerosol mass spectrometers were analysed. Collocated measurements of VOC, black carbon, NOx and CO were performed. Positive matrix factorization (PMF) analysis was performed to separate the organic fraction, identifying a number of conventional factors: hydrocarbon-like OA (HOA) related to traffic emissions, biomass burning OA (BBOA), cooking OA (COA) and secondary OA (SOA). A composition-based estimate of PM1 is defined by combining BC and NR-PM1 (C-PM1 = BC + NR-PM1). No significant difference was observed on C-PM1 concentrations between sites; OD (142 ± 117 µg m−3) compared to ND (123 ± 71 µg m−3), from post-monsoon measurements. A wider variability was observed between seasons, where pre-monsoon and monsoon showed C-PM1 concentrations lower than 60 µg m−3. A seasonal variation in C-PM1 composition was observed; SO42− showed a high contribution over pre-monsoon and monsoon seasons while NO3− and Cl− had a higher contribution in winter and post-monsoon. The main primary aerosol source was from traffic, which is consistent with the PMF analysis and aethalometer model analysis. Thus, in order to reduce PM1 concentrations in Delhi through local emission controls traffic emissions control offers the greatest opportunity. PMF-AMS mass spectra will help to improve future aerosol source apportionment studies. The information generated in this study increases our understanding of PM1 composition and OA sources in Delhi, India. Furthermore, the scientific findings provide significant information to strengthen legislation that aims to improve air quality in India.

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

“…This was mainly due to the contraction of the boundary layer during the night and early hours of the morning being more pronounced which removes possible afternoon peaks 240 from specific sources, e.g. lunch hour cooking activities (Nakoudi et al, 2019;Reyes-Villegas et al, 2020). The pre-monsoon and monsoon diurnal cycles show species concentrations, excluding nitrate and chloride, were less affected by the higher boundary layer in the afternoon.…”

“…The AMS measurements were compared to a number of co-located instruments including black carbon (BC) measurements which were taken using an Aethalometer AE-31 and corrected for by a Single Particle Soot Photometer (SP-2; Droplet Measurement Technology, Boulder, CO) (Reyes-Villegas et al, 2020). Volatile 165 organic compounds (VOC) were measured using a high-resolution proton transfer reaction mass spectrometer (PTR-QiTOF, Ionicon Analytik G.m.b.H., Innsbruck, Austria).…”

Effect of Biomass Burning on PM2.5 Composition and Secondary Aerosol Formation During Post‐Monsoon and Winter Haze Episodes in Delhi

“…Figures 1a and 1b show the temporal variation of mass concentration of PM 2.5 species (Org, NO 3 , SO 4 , NH 4 , Chl, and BC), C‐PM 2.5 (composition‐based estimate of PM 2.5 calculated as the sum of NR‐PM 2.5 and BC) and relative contribution of species to the total PM 2.5 at HK and PF site. C‐PM 2.5 based on AMS and aethalometer measurements has been used in the previous studies as a representation of PM 2.5 concentrations (Gani et al., 2019; Reyes‐Villegas et al., 2021). For the total campaign period, the mean C‐PM 2.5 concentration at HK was 82.0 ± 48.1 μg m −3 (7.5–225.3) whereas 105.7 ± 52.5 μg m −3 (14.2–235.1) at HK and PF, respectively.…”

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

“…These compounds have not been identified in published AMS spectra; however, many have pub- lished amine peaks within factors. Most studies name these factors nitrogen organic aerosol (NOA); however, some relate to specific local organic aerosol (LOA) (Aiken et al, 2009;Docherty et al, 2011;Sun et al, 2011;Saarikoski et al, 2012;Hayes et al, 2013;Bottenus et al, 2018;Zhang et al, 2018 ), and it is therefore suggested that this factor may also contain nitrile compounds.…”