1. Introduction
The new severe acute respiratory syndrome-coronavirus (SARS-CoV2) has had an unprecedented impact around the world. The spread of the 2019 coronavirus disease (COVID-19), initially identified in Wuhan in China, led to over one million cases worldwide in the first four months [
1]. The virus has affected almost all countries on the planet (235 in total), causing so far over 34 million confirmed cases and about 1,030,000 deaths [
2]. This has resulted in lockdown in many nations. The COVID-19 pandemic has substantially affected the human society, including healthcare, economic structures, and social relationships [
3].
In Italy, between the months of February and March, a series of national and regional legislative measures were issued to stop the spread of COVID-19, which radically changed the daily habits and lifestyles of citizens. The lockdown and the related implemented measures led to a sudden drop in economic activities, including a fall in road transport in many cities and a drastic reduction in the movement of citizens through the adoption of smart-working practices wherever possible.
In Italy, the Decree of the President of the Council of Ministers (DPCM) of 9 March 2020 [
4], also known as the “I stay at home” Decree, extended the measures on confinement and restriction on travel to the whole country and prohibited any form of gathering of people in public places or locations open to the public, also suspending sporting and cultural events. The DPCM of 21 March 2020 [
5], known as “Italy’s block”, blocked non-essential activities and imposed a ban on moving to different municipalities. In Italy, lockdown and travel restrictions were maintained until 3 May 2020.
Is lockdown a factor influencing air pollution?
Reducing air pollution could be considered part of an integrated approach for the protection of human health and the prevention of epidemic spread. The role of air pollution in contributing to the high levels of SARS-CoV-2 lethality in northern Italy has been hypothesized [
6,
7].
Exposure to air pollution is an important and persistent risk factor for death by different causes and for a high incidence of respiratory diseases [
8,
9]. Deaths associated with air pollution include aggravated asthma, bronchitis, emphysema, lung and heart disease, and respiratory allergies [
8]. Among the atmospheric pollutants, the focus is mainly on nitrogen dioxide (NO
2), particulate matter (PM
2.5 and PM
10), and ozone (O
3), which are frequently found at high concentrations in urban areas.
Various studies have reported a direct relationship between the spreading and contagion capacity of some viruses and the atmospheric levels and mobility of atmospheric pollutants [
10,
11]. The results provided by Zhu et al. [
12] indicated that a significant relationship exists between air pollution and COVID-19 infection, which could partially explain the effect of the national block and provide implications for the control and prevention of this new disease.
A decline in anthropogenic air pollution has been observed in countries that have responded to the COVID-19 pandemic with a total closure of all activities. Satellite data recorded by the NASA Earth Observatory showed that NO
2 concentrations in eastern and central China from the beginning of 2020 were 10–30% lower than those in comparable periods in 2019 [
13]. In particular, in Hubei province (China), strict social distancing measures that affected the main economic activities of the region were implemented from December 2019; power plants and industrial structures stopped production, and the use of vehicles decreased considerably [
14]. This led to a drastic reduction in the levels of NO
2 and fine atmospheric particulate matter [
15,
16]. The European Environment Agency found a similar decrease in air pollution in European cities [
17]. Air pollution drastically reduced as major industries and other regular businesses came to a halt, leading to a sharp reduction in NO
2 concentrations in countries such as France, Germany, Italy, and Spain [
14,
18,
19]. From 16 to 22 March 2020, Bergamo (Italy) and Barcelona (Spain) showed decreases in NO
2 of 47% and 55% compared to the same dates in 2019, respectively. The impact of the COVID-19 pandemic on air pollution measured by the United States using the federal air monitoring network showed strong reductions in fine particulate matter (PM
2.5) and NO
2, corresponding to reduced traffic and mandatory company closures [
20].
In our investigation, we explored the impact of COVID-19-relatd restrictions on the main air pollutant concentrations, CO, NO2, O3, and PM10, measured in the city of Palermo (Italy) using the municipal air-monitoring network. We used statistical and quantitative analyses of the relationships between air pollution, human mobility, and travel restrictions to infer the effects on air quality.
The objectives of this study were: (1) to compare the concentrations of the main atmospheric pollutants determined in the city of Palermo (Italy) during the pre-lockdown, lockdown, and post-lockdown periods; (2) compare the collected data with those of the same time window in the previous five years (2015–2019); and (3) evaluate the usefulness of the block as an alternative strategy for reducing the level of atmospheric pollution in the city of Palermo.
4. Conclusions
Air pollution studies should be considered as part of an integrated approach for sustainable development and the protection of human health. The national lockdown during the COVID-19 pandemic provided an opportunity to work on improving air quality. The results of this study demonstrate that anthropogenic activities strongly influence air quality. The lockdown period produced a sharp reduction in all pollutants that are closely linked to vehicular traffic. In the urban area of Palermo (Italy) from 10 March to 30 April, the concentrations of CO, NO2, and PM10 decreased to about 51%, 50%, and 45%, respectively. The period of forced block produced decreases in the concentrations of CO, NO2, and PM10 from the first six days of lockdown. The lack of a decrease of tropospheric ozone during the block due to non-linear chemical effects showed that these reductions will remain challenging, even with effective policies to reduce primary pollutants.
The findings reported here are a useful indication for competent authorities to rethink existing regulatory plans and provide assurance for the implementation of rigorous alternative measures such as short-term blocks to produce a real improvement in air quality.