Better understanding the behavior of air pollutants at shutdown times - results of a short full lockdown

Numerous studies have evaluated the effects of lockdowns during the COVID-19 pandemic, but most of them have concerned large cities and regions. This study aimed to evaluate the dynamics of air pollutants during and after the implementation of a short lockdown in the medium-sized city of Pelotas, Brazil, using hourly measurements of pollutants. The evaluation period included in this study was between August 9^th and 12^th, 2020. A machine learning model was used to investigate the expected behavior against what was observed during the study period. All pollutants presented a gradual reduction until a dynamic plateau established 48 hours after the start of the lockdown: NO₂ (↓4%), O₃ (↓34%), SO₂ (↓24%), CO (↓48%), PM₁₀ (↓82%) and PM_2.5 (↓82%). At the end of the restriction measures, the PM₁₀ and PM_2.5 levels continued to decline beyond expectations. Our findings show that these measures can positively affect the air quality in medium-sized cities.