PM1 composition and source apportionment at two sites in Delhi, India, across multiple seasons
Authors: Reyes-Villegas Ernesto , Panda Upasana , Darbyshire Eoghan , Cash James M. , Joshi Rutambhara , Langford Ben , Di Marco Chiara F. , Mullinger Neil J. , Alam Mohammed S. , Crilley Leigh R. , Rooney Daniel J. , Acton W. Joe F. , Drysdale Will , Nemitz Eiko , Flynn Michael , Voliotis Aristeidis , McFiggans Gordon , Coe Hugh , Lee James , Hewitt C. Nicholas , Heal Mathew R. , Gunthe Sachin S. , Mandal Tuhin K. , Gurjar Bhola R. ,   Shivani, Gadi Ranu , Singh Siddhartha , Soni Vijay , Allan James D. 
Published: August 2021

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.