ABSTRACT
Due to coronavirus disease 2019 (COVID-19), many cities implemented strict lockdown to stop the spread of this new disease. Consequently, it was reported lower levels of air pollution due to less human activity outdoors. The changes were registered using surface monitoring stations or satellite observations. However, modeling those environmental changes has remained a challenge because of our limitations in the emissions estimation and also, for the numerical modeling itself. In this study, the vehicular emissions were estimated for March 2020 in the megacity of São Paulo using the Vehicular Emissions INventory model (VEIN). The emissions estimation showed an increment of VOC/NO2 downtown, due to the decrease in circulation of urban transportation and light vehicles. Then, a set of Weather Research and Forecasting models with chemistry (WRF-Chem) simulations were performed with different chemical mechanisms and initial conditions. The modeled diurnal cycles represent the variations observed in March 2020 for the periods pre-lockdown, transition, and lockdown. However, it is imperative to include other sources than vehicular to have a local and comprehensive emissions inventory. Copyright © 2022 Ibarra-Espinosa, Rehbein, Freitas, Martins, Andrade and Landulfo.
ABSTRACT
This study delves into the photochemical atmospheric changes reported globally during the pandemic by analyzing the change in emissions from mobile sources and the contribution of local meteorology to ozone (O-3) and particle formation in Bogota (Colombia), Santiago (Chile), and Sao Paulo (Brazil). The impact of mobility reductions (50%-80%) produced by the early coronavirus-imposed lockdown was assessed through high-resolution vehicular emission inventories, surface measurements, aerosol optical depth and size, and satellite observations of tropospheric nitrogen dioxide (NO2) columns. A generalized additive model (GAM) technique was also used to separate the local meteorology and urban patterns from other drivers relevant for O-3 and NO2 formation. Volatile organic compounds, nitrogen oxides (NOx), and fine particulate matter (PM2.5) decreased significantly due to motorized trip reductions. In situ nitrogen oxide median surface mixing ratios declined by 70%, 67%, and 67% in Bogota, Santiago, and Sao Paulo, respectively. NO2 column medians from satellite observations decreased by 40%, 35%, and 47%, respectively, which was consistent with the changes in mobility and surface mixing ratio reductions of 34%, 25%, and 34%. However, the ambient NO2 to NOx ratio increased, denoting a shift of the O-3 formation regime that led to a 51%, 36%, and 30% increase in the median O-3 surface mixing ratios in the 3 respective cities. O-3 showed high sensitivity to slight temperature changes during the pandemic lockdown period analyzed. However, the GAM results indicate that O-3 increases were mainly caused by emission changes. The lockdown led to an increase in the median of the maximum daily 8-h average O-3 of between 56% and 90% in these cities.