Analysis of COVID-19 Lockdown Effects on Urban Air Quality: A Case Study of Monterrey, Mexico.

The COVID-19 pandemic has caused several millions of deaths and forced the world population to a new normality. This study aims to analyze the air quality variation of several gaseous pollutants (CO, NO₂, SO₂, O₃, PM₁₀, and PM_2.5) during the pre-lockdown, lockdown, and unlock period in the city of Monterrey using ground-based measurements. In this research, we proposed to use a control period of previous years to identify parameter variation due to local climate. The results showed a drastic decrease in measured contaminants during the lockdown period as follows: SO₂ (−41.9%) > PM₁₀ (−30.5%) > PM_2.5 (−25.6%) > NO₂ (−14.9%) > CO (−9.8%) compared to the control period (2017–2019). The O₃ was the only air pollutant that showed an opposite trend, increasing during lockdown (+15%) and unlock (+2.2%), whereas CO (−16.6%) and NO₂ (−30.6%) were further decreased. Moreover, using OMI/AURA satellite data, we detected a NO₂ tropospheric column reduction by −1.9% during lockdown concerning the same period in the control interval. Moreover, we found a significant improvement in the Air Quality Index (AQI) due to the lockdown. Our findings indicate an association between air pollutants and economic activity and can be used in future strategies to improve urban air quality. [ABSTRACT FROM AUTHOR]