Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes

Abstract

Delhi, India, suffers from periods of very poor air quality, but little is known about the chemical production of secondary pollutants in this highly polluted environment. During the postmonsoon period in 2018, extremely high nighttime concentrations of NOx (NO and NO2) and volatile organic compounds (VOCs) were observed, with median NOx mixing ratios of ∼200 ppbV (maximum of ∼700 ppbV). A detailed chemical box model constrained to a comprehensive suite of speciated VOC and NOx measurements revealed very low nighttime concentrations of oxidants, NO3, O3, and OH, driven by high nighttime NO concentrations. This results in an atypical NO3 diel profile, not previously reported in other highly polluted urban environments, significantly perturbing nighttime radical oxidation chemistry. Low concentrations of oxidants and high nocturnal primary emissions coupled with a shallow boundary layer led to enhanced early morning photo-oxidation chemistry. This results in a temporal shift in peak O3 concentrations when compared to the premonsoon period (12:00 and 15:00 local time, respectively). This shift will likely have important implications on local air quality, and effective urban air quality management should consider the impacts of nighttime emission sources during the postmonsoon period.

Metadata

Item Type:	Article
Authors/Creators:	Nelson, Beth S. https://orcid.org/0000-0003-4493-4086 Bryant, Daniel J. (daniel.bryant@york.ac.uk) Alam, Mohammed S. Sommariva, Roberto Bloss, William J. Newland, Mike J. (mn755@york.ac.uk) Drysdale, Will S. https://orcid.org/0000-0002-7114-7144 Vaughan, Adam R. https://orcid.org/0000-0002-7878-0719 Acton, W. Joe F. Hewitt, C. Nicholas Crilley, Leigh R. Swift, Stefan J. Edwards, Pete M. https://orcid.org/0000-0002-1076-6793 Lewis, Alastair C. https://orcid.org/0000-0002-4075-3651 Langford, Ben Nemitz, Eiko Shivani, None Gadi, Ranu Gurjar, Bhola R. Heard, Dwayne E. Whalley, Lisa K. Şahin, Ülkü A. Beddows, David C.S. Hopkins, James R. Lee, James D. https://orcid.org/0000-0001-5397-2872 Rickard, Andrew R. https://orcid.org/0000-0003-2203-3471 Hamilton, Jacqueline F. https://orcid.org/0000-0003-0975-4311
Copyright, Publisher and Additional Information:	Funding Information: The authors acknowledge Tuhin Mandal at CSIR National Physical Laboratory for his support in facilitating the measurement sites used in this project and Gareth Stewart for VOC measurements. This work was supported by the Newton Bhabha fund administered by the UK Natural Environment Research Council through the DelhiFlux (NE/P016502/1) and ASAP projects of the Atmospheric Pollution and Human Health in an Indian Megacity (APHH-India) program. The authors gratefully acknowledge the financial support provided by the UK Natural Environment Research Council and the Earth System Science Organization, Ministry of Earth Sciences, Government of India, under the Indo-UK Joint Collaboration (DelhiFlux). B.S.N. and D.J.B. acknowledge the NERC SPHERES doctoral training program for studentships. This project was undertaken on the Viking Cluster, which is a high-performance computing facility provided by the University of York. The authors are grateful for computational support from the University of York High Performance Computing service, Viking, and the Research Computing team. Publisher Copyright: © 2023 The Authors. Published by American Chemical Society.
Keywords:	air quality,atmospheric oxidation chemistry,nocturnal atmospheric chemistry,ozone,VOC
Dates:	Accepted: 24 April 2023 Published (online): 3 May 2023
Institution:	The University of York
Academic Units:	The University of York > Faculty of Sciences (York) > Chemistry (York)
Funding Information:	Funder Grant number UNSPECIFIED NE/P01643X/1 NATURAL ENVIRONMENT RESEARCH COUNCIL R8/H12/83/010
Depositing User:	Pure (York)
Date Deposited:	31 May 2023 08:20
Last Modified:	19 Apr 2025 05:41
Published Version:	https://doi.org/10.1021/acs.estlett.3c00171
Status:	Published online
Refereed:	Yes
Identification Number:	10.1021/acs.estlett.3c00171
Related URLs:	http://www.scopus.com/inward/record.url?...
Open Archives Initiative ID (OAI ID):	oai:eprints.whiterose.ac.uk:199771

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Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes

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