Elucidating the Impacts of COVID-19 Lockdown on Air Quality and Ozone
Chemical Characteristics in India
Abstract
India implemented stay-at-home order (i.e. lockdown) on 24 March 2020 to
decrease the spread of novel COVID-19, which reduced air pollutant
emissions in different sectors. The Weather Research and Forecasting
model with Chemistry (WRF-Chem) was used to study the changes in air
pollutants during the lockdown period in 2020 compared with similar
period in 2019. We found that both meteorology and lockdown emissions
contributed to daytime PM2.5 (-6% and -11%,
respectively) and ozone (-6% and -8%, respectively) reduction averaged
in April 2020 in the Indo-Gangetic Plain. However, the ozone
concentration response to reductions in its precursors (i.e.
NO2 and VOCs) due to the lockdown emissions was not
constant over the domain. While ozone concentration decreased in most
parts of the domain, it slightly increased in major cities like Delhi
and in regions with many power plants. We utilized the reaction rates
information in WRF-Chem to study the ozone chemistry. We found carbon
monoxide, formaldehyde, isoprene, acetaldehyde, and ethylene as the
major VOCs that contribute to the ozone formation in India. We used the
ratio of chemical loss of radicals with radicals and NOx, and its
corresponding formaldehyde to NO2 ratio (FNR) to find
the ozone chemical regimes. Using the upper limit of FNR transition
region (1.3), we found that most parts of India are within NOx-limited
regime while urban regions and the regions with many power plants are in
a VOC-limited regime. As a result, policy makers should study the
characteristics of a region before implementing mitigation strategies.