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 PM_2.5 (-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.