COVID-19: Has social isolation reduced the emission of pollutants in the megacity of Sao Paulo-Brazil?

The first case of COVID-19 in Brazil was registered in the city of Sao Paulo on February 26, 2020; however, restrictive measures and social distancing were only determined in the city on March 17, 2020. A partial lockdown aimed to mitigate the advance of the virus by raising the social isolation rates, by limiting the operation of several services and the mobility of the population. Thus, this study aims to analyze the relationship between the social isolation index in the city of Sao Paulo and the emission levels of the main air pollutants (PM10, PM2.5, NOx, NO, NO2, SO2 and CO), as well as air temperature. We analyzed the data collected from three urban air quality monitoring stations located in the city center of Sao Paulo from March 16, 2020 to July 20, 2020. The data for 2020 were compared with those of the previous period in 2020 and the same period in the previous 5 years (2015-2019), and also to the city's official indices of social isolation. The relationships between pollutant concentrations and the social isolation index showed that the decrease in mobility influenced the reduction in air pollution. Pollutants NO2, NOx, NO and CO had the strongest negative associations (Pearson's correlation = - 0.582; 0.481; - 0.433 and - 0.367, respectively). Our results showed that the partial lockdown (from March 17, 2020, to July 20, 2020) had a positive impact on air quality, with a reduction in the emission of pollutants NO (31.75%), NO2 (20.60%), NOx (27.21%) and CO (29.95%). The greatest reductions in the emission of pollutants were observed when the social isolation index reached an average of 52.20%. Small negative fluctuations in the social isolation index broke the most significant reductions observed at the beginning of social isolation.