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: https://orcid.org/0000-0002-6968-5197; Nemitz, Eiko ORCID: https://orcid.org/0000-0002-1765-6298; 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. https://doi.org/10.1021/acs.estlett.3c00171

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Official URL: http://dx.doi.org/10.1021/acs.estlett.3c00171

Abstract/Summary

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):	https://doi.org/10.1021/acs.estlett.3c00171
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 Chemistry
Date made live:	07 Nov 2023 13:36 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/535580

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1021/acs.estlett.3c00171

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