Impacts of the COVID-19 lockdown on air quality and its association with human mortality trends in megapolis Mexico City.

Mexico City is the second most populated city in Latin America, and it went through two partial lockdowns between April 1 and May 31, 2020, for reducing the COVID-19 propagation. The present study assessed air quality and its association with human mortality rates during the lockdown by estimating changes observed in air pollutants (CO, NO, O, SO, PM and PM) between the lockdown (April 1-May 31) and prelockdown (January 1-March 31) periods, as well as by comparing the air quality data of lockdown period with the same interval of previous 5 years (2015-2019). Concentrations of NO (- 29%), SO (- 55%) and PM (- 11%) declined and the contents of CO (+ 1.1%), PM (+ 19%) and O (+ 63%) increased during the lockdown compared to the prelockdown period. This study also estimated that NO, SO, CO, PM and PM reduced by 19-36%, and O enhanced by 14% compared to the average of 2015-2019. Reduction in traffic as well as less emission from vehicle exhausts led to remarkable decline in NO, SO and PM. The significant positive associations of PM, CO and O with the numbers of COVID-19 infections and deaths, however, underscored the necessity to enforce air pollution regulations to protect human health in one of the important cities of the northern hemisphere. Graphical abstract.