Abstract
To control the spread of COVID-19, in March 2020 exceptional restrictive measures were taken imposing a radical change in the lifestyle of millions of citizens around the world, albeit for a short period of time. The national lockdown, which in Italy lasted from 10 March to 18 May 2020, was a unique opportunity to observe the variation in air quality in urban environments in a condition of almost total traffic block and a strong reduction in work activities. In this paper, the data from seventeen urban monitoring sites in Tuscany are presented by comparing PM and NO2 of the two months before the start of the lockdown and the two after with the corresponding months of the previous three years. The results show that the total load of PM2.5 and PM10 decreased but it did not exhibit significant changes compared to previous years, while NO2 undergoes a drastic reduction. For three of these sites, the chemical composition of the collected samples was measured by thermo-optical, ion chromatography and PIXE analysis, and the application of multivariate PMF analysis allowed the PM10 source identification and apportionment. Thanks to these analyses it was possible to explain the low sensitiveness of PM10 to the lockdown effects as due to different, sometimes opposite, behaviors of the different sources that contribute to PM. The results clearly indicated a decline in pollution levels related to urban traffic and an increase in the concentration of sulfate for all sites during the lockdown period.
Highlights
The national lockdown, which in Italy lasted from 10 March to 18 May 2020, was a unique opportunity to observe the variation in air quality in urban environments in a condition of almost total traffic block and a strong reduction in work activities
The results show that the total load of PM2.5 and PM10 decreased but it did not exhibit significant changes compared to previous years, while NO2 undergoes a drastic reduction
From the samples of the three sites dedicated to chemical analysis (FI-3, FI-1, and PO-2), combining the results of ion chro215 matography, PIXE and thermo-optical analysis, a dataset was obtained with a total of 33 chemical species, including the mass of PM10
Summary
Starting from the city of Wuhan, the capital of Hubei province of China, in early 2020, the SARS-CoV-2 virus quickly spread around the world becoming an established pandemic by the World Health Organization (WHO, 2021). For example, starting from March, with the arrival of spring, the air quality improves, mainly due to the enhanced dispersion capabilities of the atmosphere (e.g., the greater height of the mixing layer), except for the pollutants produced by photochemical reaction, like sulphates and ozone, which increases with the warm months (Gerasopoulos et al, 55 2006) This indicates that the generation of secondary pollutants is not affected only by emission reduction but it is influenced by multiple factors that make the many studied cases hardly comparable. Such analyses can be useful in view of possible future policy interventions aimed at reducing the load of particulate matter in urban centers
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