Abstract
The increasing concentration of human activities in cities has been leading to a worsening in air quality, thus negatively affecting the lives and health of humans living in urban contexts. Transport is one of the main sources of pollution in such environments. Several local authorities have therefore implemented strict traffic-restriction measures. The aim of this paper is to evaluate the effectiveness and limitations of these interventions, by analyzing the relationship between traffic flows and air quality. The used dataset contains concentrations of NO, NO2, NOx and PM10, vehicle counts and meteorology, all collected during the COVID-19 lockdown in the city of Padova (Italy), in which severe limitations to contain the spread of the virus simulated long and large-scale traffic restrictions in normal conditions. In particular, statistical tests, correlation analyses and multivariate linear regression models were applied to non-rainy days in 2020, 2018 and 2017, in order to isolate the effect of traffic. Analysis indicated that vehicle flows significantly affect NO, NO2, and NOx concentrations, although no evidence of a relationship between traffic and PM10 was highlighted. According to this perspective, measures to limit traffic flows seem to be effective in improving air quality only in terms of reducing nitrogen oxide.
Highlights
In recent years, many cities have undergone a worsening in air quality [1,2,3], due to the increasing concentration of human activities, which produce polluting emissions [4,5,6]
The used dataset contains concentrations of NO, NO2, NOx and PM10, vehicle counts and meteorology, all collected during the COVID-19 lockdown in the city of Padova (Italy), in which severe limitations to contain the spread of the virus simulated long and large-scale traffic restrictions in normal conditions
Since this paper focuses on the effect of reduced traffic on air quality on a city scale, using data obtained both before and during the lockdown due to the COVID-19 pandemic, the distances between the air quality monitoring stations and traffic detectors were quite high, it is worth noting that the drastic decrease in traffic flows in the lockdown period occurred on a national scale; for this reason, data obtained at a local level may represent the situation on larger scales
Summary
Many cities have undergone a worsening in air quality [1,2,3], due to the increasing concentration of human activities, which produce polluting emissions [4,5,6]. Among other pollutants, internal combustion engines emit nitrogen oxides [12] like NO and NOx (mainly from diesel engines) [1,13,14], which generate NO2 [14,18,19] and particulate matter [5,12,13] such as PM10 [2], which originates through mechanical processes [12] Both primary and secondary pollutants are transported far from roads, worsening the air quality of whole urban areas [1,20]. The United Nations included the creation of sustainable cities and communities as one of the 17 Sustainable Development Goals in agenda 2030, in which sustainable transport is one of the themes of several targets and goals [22]
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