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 ORCID:; Nemitz, Eiko; Shivani, ; 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.. 2023 Extreme concentrations of nitric oxide control daytime oxidation and quench nocturnal oxidation chemistry in Delhi during highly polluted episodes. Environmental Science & Technology Letters, 10 (6). 520-527.

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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 post-monsoon period in 2018, extremely high night-time 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 night-time concentrations of oxidants, NO3, O3, and OH, driven by high night-time NO concentrations. This results in an atypical NO3 diel profile, not previously reported in other highly polluted urban environments, significantly perturbing night-time 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 pre-monsoon 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 night-time emission sources during the post-monsoon period.

Item Type: Publication - Article
Digital Object Identifier (DOI):
UKCEH and CEH Sections/Science Areas: Atmospheric Chemistry and Effects (Science Area 2017-)
ISSN: 2328-8930
Additional Information. Not used in RCUK Gateway to Research.: Open Access paper - full text available via Official URL link.
Additional Keywords: air quality, atmospheric oxidation chemistry, nocturnal atmospheric chemistry, ozone, VOC
NORA Subject Terms: Atmospheric Sciences
Date made live: 07 Nov 2023 13:36 +0 (UTC)

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