São Paulo's atmospheric pollution reduction and its social isolation effect, Brazil

Abstract

Since January 2020, studies report reductions in air pollution among several countries due to social isolation measures, which have been adopted in order to contain the coronavirus outbreak progress (COVID-19). This study aims to evaluate the change in the atmospheric pollution levels by NO and NO₂ in São Paulo City for the social isolation period. The NO and NO₂ hourly concentrations were obtained through air quality monitoring stations from CETESB, from January 14, 2020 to April 12, 2020. Mann-Kendall and the Pettitt tests were performed in the air pollutant time series. We observed an overall negative trend in all stations, indicating a decreasing temporal pattern in concentrations. Regarding NO, the highest absolute decrease rates were observed in the Congonhas (- 6.39 μg m^-3 month^-1) and Marginal Tietê (- 6.19 μg m^-3 month^-1) stations; regarding NO₂, the highest rates were observed in the Marginal Tietê (- 4.45 μg m^-3 month^-1) and Cerqueira César (- 4.34 μg m^-3 month^-1) stations. In addition, we identified a turning point in the NO and NO₂ series trends that occurred close to the start date of the social isolation period (March 20, 2020). Moreover, from statistical analysis, it was found that NO₂ is a suitable surrogate for monitoring economic activities during social isolation periods. Thus, we concluded that social isolation measures implemented on March 20, 2020 caused significant changes in the air pollutant concentrations in the city of São Paulo (as high as - 200% in NO₂ levels).

Keywords: Air pollution; COVID-19; Coronavirus outbreak; NO2; São Paulo.

Fig. 1

Geographic delimitation of the study area (São Paulo municipality) and location of the stations used in the study

Fig. 2

Time series of daily mean NO (left) and NO₂ (right) concentration, in units of μg m⁻³, in the period between January 14th and April 12th, 2020. Note: the dashed vertical lines indicate the intervention points determined via Pettitt’s test

Fig. 3

Daily precipitation series in millimeters. The highlighted gray area is the range of intervention points observed at the stations analyzed for NO.

Fig. 4

Daily concentration percentage variation of NO (top) and NO₂ (bottom) in the period from March 15th to March 30th in 2020 at the stations Cerqueira César, Congonhas, Marginal Tietê, Parque Dom Pedro II, and Pinheiros