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This study analyses the relationship between Covid-19 and air pollutants resulting from transportation activities by addressing two research questions. First, it examines the quantitative impacts of Covid-19 on emissions/concentrations. In this case, the results are dependent on the temporal horizon and political measures introduced to control the virus. Greenhouse gases (GHGs) and nitrogen oxides (NOx) exhibit a strong correlation with reduced road traffic, while the influence of transportation on other criteria pollutants (CO, SO2, and PMx) is not univocally demonstrated. Second, the study analyses specific modes (e.g. air transport), systems (e.g. public transport), and sectors (e.g. freight transport). The generalised decrease in emissions is a consequence of reduced travel demand; however, this is not true for specific sectors, such as last-mile freight delivery or private flights, which show an increase in emissions. Moreover, unitary values register an increase in most cases, indicating a reduction in environmental effectiveness due to a modal shift towards private solutions and a reduction in the public transport occupancy rates. In the post-pandemic world, a significant issue arises when travel demand increases but the modal share is less responsive to returning to previous levels. Several research lines stem from these outcomes, ranging from technical issues (e.g. modelling safety perception in modal choice) to the evaluation of specific measures (e.g. curbing private mobility and adopting fuel regulations). Another promising area of research involves exploring the combination of Covid-19 with other transport-related drivers, such as automation and alternative fuels. Additionally, investigating the coherence between the effects of Covid-19 and long-term decarbonisation policies is an important research direction.
Cavallaro et al. (Mon,) studied this question.