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

Nelson, Beth S.; Bryant, Daniel J.; Alam, Mohammed S.; Sommariva, Roberto; Bloss, William J.; Newland, Mike J.; Drysdale, Will S.; Vaughan, Adam R.; Acton, W. Joe F.; Hewitt, C. Nicholas; Crilley, Leigh R.; Swift, Stefan J.; Edwards, Pete M.; Lewis, Alastair C.; Langford, Ben; Nemitz, Eiko; Gadi, Ranu; Gurjar, Bhola R.; Heard, Dwayne E.; Whalley, Lisa K.; Şahin, Ülkü A.; Beddows, David C. S.; Hopkins, James R.; Lee, James D.; Rickard, Andrew R.; Hamilton, Jacqueline F.

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.

Citation

Nelson, B. S., Bryant, D. J., Alam, M. S., Sommariva, R., Bloss, W. J., Newland, M. J., …Hamilton, J. F. (2023). Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes. Environmental Science and Technology Letters, 10(6), 520-527. https://doi.org/10.1021/acs.estlett.3c00171

• Journal Article Type: Article
• Acceptance Date: Apr 24, 2023
• Online Publication Date: May 3, 2023
• Publication Date: Jun 13, 2023
• Deposit Date: Sep 28, 2023
• Publicly Available Date: Oct 4, 2023
• Journal: Environmental Science & Technology Letters
• Electronic ISSN: 2328-8930
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 10
• Issue: 6
• Pages: 520-527
• DOI: https://doi.org/10.1021/acs.estlett.3c00171
• Keywords: Health, Toxicology and Mutagenesis; Pollution; Waste Management and Disposal; Water Science and Technology; Ecology; Environmental Chemistry
• Public URL: https://nottingham-repository.worktribe.com/output/20828303
• Publisher URL: https://pubs.acs.org/doi/10.1021/acs.estlett.3c00171