LAUSR

Abstract From May 21st to 31st, 2018, a truck driver strike greatly decreased all vehicle activity in Brazil. We evaluated the concentrations of criteria pollutants in seven different microenvironments during this period in the Sao Paulo Megacity. Results were evaluated by violin plots, the Kruskal-Wallis test and diurnal cycles, comparing the year 2018 to an average of 4 previous years. Primary pollutants (CO and NO) decreased by 50% in 2018, predominantly in roadside (RDS) locations. NO2, PM10, and PM2.5 did not decrease as much, suggesting the relevance of secondary reactions and other sources (ex: fires). Ozone increased significantly (about 30–50%), possibly due to favourable atmospheric conditions (solar radiation) and changes in the NOx/VOCs ratio caused by the decrease in NO. Our findings help to better assess the role of vehicular emissions and provide insights on the impacts of interruption of activities (ex: during lockdowns) over air quality in metropolitan environments.