Anatomy of the winter 2017 air quality emergency in Delhi Gufran Beig a, ⁎, Reka Srinivas a , Neha S. Parkhi a , G.R. Carmichael b , Siddhartha Singh c , Saroj K. Sahu d , Aditi Rathod a , Sujit Maji a a Indian Institute of Tropical Meteorology, Pune 411008, India b CGRER, The University of Iowa, Iowa City, USA c India Meteorological Department, New Delhi, India d Utkal University, Bhubaneswar, India HIGHLIGHTS • A thick haze triggered emergency con- dition in Delhi during winter 2017. • Monsoon dynamics and dust storm played a pivotal role in deterioration of air quality. • Heavy aerosol load altered land skin surface air temperature and it helps to fast dispersion. GRAPHICAL ABSTRACT abstract article info Article history: Received 24 December 2018 Received in revised form 2 April 2019 Accepted 23 April 2019 Available online 02 May 2019 Editor: Pavlos Kassomenos The Indian capital Delhi experienced an environmental emergency in early November 2017 when levels of toxic PM 2.5 particles surpassed WHO guidelines by 25 times (11 times by Indian Standards) for a prolonged period of a week (peak 24 h average ~650 μg/m 3 ). We hereby demonstrate the role that monsoon dynamics played in linking and mixing dust emitted from a large natural dust storm, 3000 km away in the Middle East, with smoke from ag- riculture fires in northwest India. This dust and smoke rich air was then transported to Delhi where, under stag- nant conditions, it mixed with local emissions resulting in very high pollution levels. The heavy aerosol-laden air altered the land-skin surface air temperature difference resulting in increased surface wind speeds, favouring faster dispersion and an unusual sharp decline in PM 2.5 (PM 2.5 –110 μg/m 3 ). Understanding the multi-scale nature of such events is important in improving our abilities to forecast these events and in developing effective air qual- ity management strategies for the mega cities. © 2019 Elsevier B.V. All rights reserved. Keywords: Air quality Delhi PM 2.5 particles Monsoon Dust storm Science of the Total Environment 681 (2019) 305–311 ⁎ Corresponding author. E-mail address: beig@tropmet.res.in (G. Beig). https://doi.org/10.1016/j.scitotenv.2019.04.347 0048-9697/© 2019 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv