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 and
agricultural crop losses, and adversely affect human health. During October 2018,
concentrations of speciated non-methane hydrocarbon 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 Emissions Database for Global Atmospheric Research (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.
A temporally and spatially resolved validation of emission inventories by measurements of ambient volatile organic compounds in Beijing, China