Abstract
Delhi, the capital of India, suffers from heavy local emissions as well as regional transport of air pollutants, resulting in severe aerosol loadings. To determine the sources of these pollutants, we have quantified the mass concentrations of 26 elements in airborne particles, measured by an online X-ray fluorescence spectrometer with time resolution between 30 min and 1 h. Measurements of PM10 and PM2.5 (particulate matter <10 μm and < 2.5 μm) were conducted during two consecutive winters (2018 and 2019) in Delhi. On average, 26 elements from Al to Pb made up ~25% and ~19% of the total PM10 mass (271 μg m−3 and 300 μg m−3) in 2018 and 2019, respectively. Nine different aerosol sources were identified during both winters using positive matrix factorization (PMF), including dust, non-exhaust, an S-rich factor, two solid fuel combustion (SFC) factors and four industrial/combustion factors related to plume events (Cr-Ni-Mn, Cu-Cd-Pb, Pb-Sn-Se and Cl-Br-Se). All factors were resolved in both size ranges (but varying relative concentrations), comprising the following contributions to the elemental PM10 mass (in % average for 2018 and 2019): Cl-Br-Se (41.5%, 36.9%), dust (27.6%, 28.7%), non-exhaust (16.2%, 13.7%), S-rich (6.9%, 9.2%), SFC1 + SFC2 (4%, 7%), Pb-Sn-Se (2.3%, 1.66%), Cu-Cd-Pb (0.67%, 2.2%) and Cr-Ni-Mn (0.57%, 0.47%). Most of these sources had the highest relative contributions during late night (22:00 local time (LT)) and early morning hours (between 03:00 to 08:00 LT), which is consistent with enhanced emissions into a shallow boundary layer. Modelling of airmass source geography revealed that the Pb-Sn-Se, Cl-Br-Se and SFC2 factors prevailed for northwest winds (Pakistan, Punjab, Haryana and Delhi), while the Cu-Cd-Pb and S-rich factors originated from east (Nepal and Uttar Pradesh) and the Cr-Ni-Mn factor from northeast (Uttar Pradesh). In contrast, SFC1, dust and non-exhaust were not associated with any specific wind direction.
Highlights
Asia is one of the most important regions of the world in context of atmospheric aerosol loading, because of the presence of fast-growing economies such as India and China
Cl and Si accounted for 33% and 25%, respectively in PM10el in 2018, and 36% and 21%, respectively in 2019
Elements measured by the Xact represent ~25% in 2018 and ~ 19% in 2019 of total PM10, with the dominant elements consisting of Cl, S and crustal material (i.e., Si, Ca, Ti, Fe)
Summary
Asia is one of the most important regions of the world in context of atmospheric aerosol loading, because of the presence of fast-growing economies such as India and China. Industrialization, urbanization, economic growth and the associated increase in energy demands have resulted in a severe deterioration of urban air quality (Li et al, 2019). The large number of pollution sources (concentrated in urban areas with dense housing, traffic and industry) may result in high pollution levels; especially if pollution controls lag behind city growth. Identification of aerosol sources is a priority for assessing adequate air quality control strategies, aerosol health impacts and climate change effects. Several approaches have been used for this task, e.g. source-oriented and receptor-oriented air quality models (Amato et al, 2011; Li et al, 2012; Pant and Harrison, 2012; Belis et al, 2019; and references therein), stable and radioisotope composition of certain species (Aggarwal et al, 2013; Kirillova et al, 2014; Wang et al, 2012; Zhang et al, 2015) and chemical markers (Simoneit et al, 1999). Most of the elements associated with fine particles are non-volatile in nature (with the notable exception of e.g. Cl), the elemental composition of particles remains unchanged even though they tend to undergo long-range atmospheric transport (Morawska and Zhang, 2002)
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