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 a result of anthropogenic activities. Organic aerosols (OAs) 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 their processes in urban environments is still limited. This is important particularly in India, as Delhi is a massive, inhomogeneous conurbation, where we would expect the apportionment and concentrations to vary depending on where in Delhi the measurements/source apportionment is performed, indicating the need for multisite 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, sulfate, chloride and organic aerosols) of four aerosol mass spectrometers were analysed. Collocated measurements of volatile organic compounds, black carbon, NOx and CO were performed. Positive matrix factorisation (PMF) analysis was performed to separate the organic fraction, identifying a number of conventional factors: hydrocarbon-like OAs (HOAs) related to traffic emissions, biomass burning OAs (BBOAs), cooking OAs (COAs) and secondary OAs (SOAs). A composition-based estimate of PM1 is defined by combining black carbon (BC) and NR-PM1 (C-PM1= BC + NR-PM1). No significant difference was observed in C-PM1 concentrations between sites, OD (142 ± 117 µg m−3) compared to ND (123 ± 71 µg m3), 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 emission control offers the greatest opportunity. PMF–aerosol mass spectrometer (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.
Highlights
Air pollution in urban environments has been shown to have a negative impact on human health, in megacities
No significant difference was observed in C-PM1 concentrations between sites, Old Delhi (OD) (142 ± 117 μg m−3) compared to New Delhi (ND) (123 ± 71 μg m3), from post-monsoon measurements
Lower aerosol concentrations were observed in pre-monsoon and seasons with C-PM1 average concentrations lower than 40 μg m−3 in PreM_ND_H1 and Mon_OD_H2, with Organic aerosols (OAs) being the component with the leading contributor to PM1
Summary
Air pollution in urban environments has been shown to have a negative impact on human health, in megacities. The World Health Organization (WHO) stated that in 2016 about 90 % of the global population living in urban environments was exposed to particulate matter concentrations exceeding the WHO air quality guidelines Previous studies have identified ambient fine particle concentrations, the submicron fraction lower than or equal to 1 μm, to have detrimental effects on health (PM1) (Pope et al, 2002; Ramgolam et al, 2009). OAs are composed of thousands of different chemical species and are difficult to study due to a variety of sources and processes. In 2016, a BC network in India was initiated with 16 Aethalometers (Laskar et al, 2016); the availability of these instruments allowed the study of BC sources in different environments (Rajesh and Ramachandran, 2017; Kolhe et al, 2018; Nazeer Hussain et al, 2018)
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