We studied the atmospheric CO2 levels at 12 sites in the city of Kolkata during April, 2019 (pre-COVID-19 phase) and April, 2020 (lockdown phase due to COVID-19). Significant temporal variation of CO2 level was observed (p < 0.01), but no statistically significant variation was observed between sites. The interpretation of the results can be substantiated with the lockdown effect due to COVID-19 in the city on account of complete closure of industries, transports, markets, shopping malls, recreation units, construction works etc. which are the main sources of CO2 emission. The patchy vegetation in some pockets of the city (like Deshbandhu Park and Tala Park) did not allow the atmospheric CO2 level to have a deep dip as the previous CO2 level in these sites were not very high due to carbon storage potential of the floral species.