Air Quality Assessment in São Paulo, Brazil during Covid-19 pandemic: links between isolation rates and pollutants

Abstract:

The COVID-19 pandemic has been causing measures of social isolation and a slowdown in economic activities worldwide. In Brazil, cases of the disease started to be reported in late February. Although there was no complete lockdown in the country, in São Paulo, the epicenter of the pandemic in Brazil, with more than twenty thousand deaths to date, the state decree determined the closure of schools, universities, restaurants, cultural spaces such as cinemas, theaters and concert halls, among other non-essential activities starting on March 23th. In addition, although voluntary, social isolation was strongly encouraged by the state government as much as possible. Nevertheless, few actions were taken in order to provide legal penalties for breaking the quarantine. The implementation of these measures led to the reduction of overall traffic and displacement of people; however, the isolation rates show a variation over time from the beginning of quarantine until now, and also geographical variability depending on the municipality. For this reason, the state government created an isolation index that gathers aggregated and anonymized information on population mobility. The State of São Paulo is the most populous and is responsible for about 1/3 of Brazil's GDP. The important economic activity also renders the region with the greatest anthropogenic pollution, and in the city of São Paulo, air quality indexes are eventually above recommended standard limits. Focusing on the different isolation periods during the quarantine, we use both remote sensing from satellites and in-situ measurements (from air quality stations operated by the State Environmental Agency) to investigate the air pollutant concentration variation due to the reduction of economic activities. We compare trace gases concentrations such as NOx, SO₂, HCHO during different periods based on the isolation index. We analyze the trends in concentrations and evaluate the correlation between isolation rates and pollutants which preliminary results show a negative correlation. The assessment of air pollutants responses to this unprecedented emission reduction period will be valuable in guiding public policies and control strategies for atmospheric pollution.