Assessing the immediate impact of COVID-19 lockdown on the air quality of Kolkata and Howrah, West Bengal, India

The worldwide spread of COVID-19 caused a nationwide lockdown in India from 24 March 2020 and was further extended up to 3 May 2020 to break off the transmission of novel Coronavirus. The study is designed to assess the changes in air quality from the pre-lockdown period to the during lockdown period in Kolkata and Howrah municipal corporation, West Bengal, India. GIS-based techniques include the spatial and temporal distribution of pollutants using interpolation method, and on the other hand, statistical methods like analysis of variance (ANOVA) was applied to determine the mean differences two phases and correlation matrix helps to understand the changing association of the pollutants in pre- and during lockdown phases. Significant correlations have been found among the pollutants, ANOVA (Two-Way) has shown the significant mean difference of NAQI between the two phases, F(1,611) = 465.723, p < 0.0001; pairwise comparison for Ballygunge has shown the highest mean difference 108.194 at p < 0.0001 significant level between lockdown and pre-lockdown phase. Significant positive correlation has been found between PM_2.5, PM₁₀ (0.99*); PM_2.5, NO₂ (0.81*); PM₁₀, NO₂ (0.81*); CO, NO₂ (0.77*) and some negative correlations have also been found between O₃, NO (- 0.15); O₃ and NH₃ (- 0.36) in the pre-lockdown phase. The reduction amount of mean concentration from the pre-lockdown phase to during lockdown of the main pollutants like PM_2.5, PM₁₀ and NO₂ are ~ 58.71%, ~ 57.92% and ~ 55.23%. Near Rabindra Bharati University constant emission of PM_2.5, 10 and NO₂ have been recorded due to the nearby Cossipore thermal power station.