A146-0016
Understanding in-situ ozone production in Delhi, India

Monday, 14 December 2020
Poster
Beth Nelson1, Gareth Stewart1, Will Stephen Drysdale1, Mike Newland1, Adam Vaughan2, Rachel Dunmore2, Jacqueline Hamilton2, James R Hopkins2,3, Andrew R Rickard2,3, James D Lee2,3, W. Joe F. Acton4, C Nick Hewitt4, Leigh Crilley5, Mohammed Salim Alam5, William Bloss5, Lisa Whalley6, Eiko Nemitz7 and Ranu Gadi8, (1)University of York, Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, York, YO10, United Kingdom, (2)University of York, Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, York, United Kingdom, (3)National Centre for Atmospheric Science, York, United Kingdom, (4)University of Lancaster, Lancaster Environment Centre, Lancaster, United Kingdom, (5)University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom, (6)University of Leeds, School of Chemistry, Leeds, LS2, United Kingdom, (7)Centre for Ecology and Hydrology, Edinburgh, United Kingdom, (8)Indira Gandhi Delhi Technical University for Women, Applied Sciences & Humanities, Delhi, India
Abstract:
Delhi suffers from some of the poorest air quality in the world. While ambient NO2 and particulate matter (PM) concentrations have received considerable attention, ozone (O3) levels are often ignored. High levels of O3 can adversely affect human health, leading to respiratory problems. With recent studies suggesting a reduction in PM in China is leading to increased surface-level O3 production,1 it is important to assess the chemical processes in Delhi’s atmosphere. To identify the main chemical drivers of O3 production, detailed analysis of its photochemical precursor species is required.

During May/June (pre-monsoon) and October (post-monsoon) 2018, concentrations of a large range of speciated VOCs (C2-C13), oxygenated VOCs (o-VOCs), NOx, HONO, CO and O3, and spectral radiometry, were continuously measured at an urban site in Old Delhi. During the pre-monsoon campaign, O3 concentrations regularly breached recommended WHO 8-hour exposure limit of 50 ppbv, with daytime peaks in excess of 190 ppbv.

Observations from both campaigns reveal very high concentrations of aromatic and o-VOCs, known to play an important role in in-situ O3 formation, with total BTEX (benzene, toluene, ethylbenzene, xylenes) exceeding 150 ppbv. We also compare the relative contributions of anthropogenic and biogenic VOCs to O3 production, which highlights the importance of unusually high night-time levels of reactive monoterpenes in Delhi.

The sensitivity of O3 formation to changes in VOC and NOx concentrations, photolysis rates and HO2 radical uptake to PM, is explored using an observationally constrained photochemical box model, incorporating the Master Chemical Mechanism (MCMv3.3.1, mcm.york.ac.uk) into the AtChem2 modelling toolkit.2 The model was constrained to measurements of 47 VOCs, NO, CO, HONO, 34 photolysis rates, aerosol surface area, and meteorological observations. This work probes the chemical processes that drive in-situ O3 production in Delhi’s atmosphere, highlighting the importance of using improved speciation of VOCs over standard regulatory measurements, which will aid the development of pollution control strategies.

  1. Li et al., PNAS, 2018, 116 (2), 422-427
  2. Sommariva et al., Geosci. Model Dev., 2020, 13, 169-183
<< Previous Abstract | Next Abstract