12 Apr 2021

12 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

In situ Ozone Production is highly sensitive to Volatile Organic Compounds in the Indian Megacity of Delhi

Beth S. Nelson1, Gareth J. Stewart1, Will S. Drysdale1,2, Mike J. Newland1, Adam R. Vaughan1, Rachel E. Dunmore1, Pete M. Edwards1, Alastair C. Lewis1,2, Jacqueline F. Hamilton1, W. Joe F. Acton3,a, C. Nicholas Hewitt3, Leigh R. Crilley4,b, Mohammed S. Alam4, Ülkü A. Şahin5, David C. S. Beddows2,4, William J. Bloss4, Eloise Slater6, Lisa K. Whalley6,7, Dwayne E. Heard6, James M. Cash8, Ben Langford8, Eiko Nemitz8, Roberto Sommariva4, Sam Cox9, Shivani10,c, Ranu Gadi10, Bhola R. Gurjar11, James R. Hopkins1,2, Andrew R. Rickard1,2, and James D. Lee1,2 Beth S. Nelson et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, University of York, UK
  • 2National Centre for Atmospheric Science, University of York, UK
  • 3Lancaster Environment Centre, Lancaster University, Lancaster, UK
  • 4School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT, Birmingham, UK
  • 5Istanbul University-Cerrahpasa, Engineering Faculty, Environmental Engineering Department, Avcilar, Istanbul, Turkey
  • 6School of Chemistry, University of Leeds, LS2 9JT, UK
  • 7National Centre for Atmospheric Science, University of Leeds, LS2 9JT, UK
  • 8UK Centre for Ecology and Hydrology, Edinburgh, UK
  • 9Research Software Engineering Team, University of Leicester, UK
  • 10Indira Gandhi Delhi Technical University for Women, Delhi, India
  • 11Indian Institute of Technology. Roorkee, India
  • anow at: School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT, Birmingham, UK
  • bnow at: Department of Chemistry, York University, Toronto, Ontario, Canada
  • cnow at: Department of Chemistry, Miranda House, Delhi University, India

Abstract. The Indian megacity of Delhi suffers from some of the poorest air quality in the world. While ambient NO2 and particulate matter (PM) concentrations have received considerable attention in the city, high ground level ozone (O3) concentrations are an often overlooked component of pollution. O3 can lead to significant ecosystem damage, agricultural crop losses, and adversely affect human health. During October 2018, concentrations of speciated non-methane hydrocarbons volatile organic compounds (C2 – C13), oxygenated volatile organic compounds (o-VOCs), NO, NO2, HONO, CO, SO2, O3, and photolysis rates, were continuously measured at an urban site in Old Delhi. These observations were used to constrain a detailed chemical box model utilising the Master Chemical Mechanism v3.3.1. VOCs and NOx (NO + NO2) were varied in the model to test their impact on local O3 production rates, P(O3), which revealed a VOC-limited chemical regime. When only NOx concentrations were reduced, a significant increase in P(O3) was observed, thus VOC co-reduction approaches must also be considered in pollution abatement strategies. Of the VOCs examined in this work, mean morning P(O3) rates were most sensitive to monoaromatic compounds, followed by monoterpenes and alkenes, where halving their concentrations in the model led to a 15.6 %, 13.1 % and 12.9 % reduction in P(O3), respectively. P(O3) was not sensitive to direct changes in aerosol surface area but was very sensitive to changes in photolysis rates, which may be influenced by future changes in PM concentrations. VOC and NOx concentrations were divided into emission source sectors, as described by the EDGAR v5.0 Global Air Pollutant Emissions and EDGAR v4.3.2_VOC_spec inventories, allowing for the impact of individual emission sources on P(O3) to be investigated. Reducing road transport emissions only, a common strategy in air pollution abatement strategies worldwide, was found to increase P(O3), even when the source was removed in its entirety. Effective reduction in P(O3) was achieved by reducing road transport along with emissions from combustion for manufacturing and process emissions. Modelled P(O3) reduced by ~20 ppb h−1 when these combined sources were halved. This study highlights the importance of reducing VOCs in parallel with NOx and PM in future pollution abatement strategies in Delhi.

Beth S. Nelson et al.

Status: open (until 13 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-278', Anonymous Referee #1, 30 Apr 2021 reply

Beth S. Nelson et al.

Data sets

(APHH India) Megacity Delhi atmospheric emission quantification, assessment and impacts (DelhiFlux) Beth S. Nelson, Gareth J. Stewart, Will S. Drysdale, Adam R. Vaughan, Rachel E. Dunmore, Jacqueline F. Hamilton, W. Joe Acton, Leigh R. Crilley, Mohammed S. Alam, Lisa K. Whalley, Ben Langford, Eiko Nemitz, James R. Hopkins

Beth S. Nelson et al.


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Short summary
Ozone production at an urban site in Delhi is sensitive to volatile organic compound (VOC) concentrations, particularly those of the aromatic, monoterpene and alkene VOC class. The change in ozone production by varying atmospheric pollutants according to their sources, as defined in an emissions inventory, is investigated. The study suggests that reducing road transport emissions alone does not reduce reactive VOCs in the atmosphere enough to perturb an increase in ozone production.