The effect of COVID-19 on the distribution of PM10 pollution classes of vehicles: Comparison between 2020 and 2018.

A recent study by Pini et al. (2021), focusing on year 2018, demonstrated that different strategies should be considered in different Italian cities to mitigate the effects of PM10 pollution produced by circulating cars and commercial vehicles. The current study focuses on year 2020, considering the same ten Italian cities. This new study relies on the estimation of specific indices used to assess the size of the different circulating vehicle fleets (vehicle yearly mileage, diesel-fuel car and LCV fleet dimension, etc.) and their impact on PM10 pollution (Strength of Pollution). Results for 2020, severely affected by vehicular restrictions associated with COVID-19, indicate the need to adopt PM10 pollution reduction strategies for the various cities partially different from those identified earlier. For example, Euro 4 cars is the fleet having the highest impact on PM10 pollution in Rome (emitting 3,3 times more than Euro 6 vehicles), while in Milan the most polluting vehicles are Euro 0 cars (emitting 2 times more than Euro 6 vehicles). In Naples, Euro 0 cars emit 12,5 times more than Euro 6 vehicles. A careful look into the results also reveals that, for all considered cities, the three top fleets in terms of PM10 pollution always include Euro 4 or a higher Euro category fleet and a lower Euro category fleet (Euro 0 or Euro 3). These values were validated based on the use of pollution data from ground monitoring stations, which also allowed estimating the atmospheric mixing layer height. Results from the paper suggest that different incentivization policies have to be considered for the different considered cities. For example, in Naples the allocation of incentives should be ~60% towards new vehicles and ~40% towards recent used (i.e. second-hand) non-diesel vehicles, while in Florence it should be ~90% towards ECVs and ~10% towards recent used non-diesel vehicles.

Impact of the different vehicle fleets on PM10 pollution: Comparison between the ten most populous Italian metropolitan cities for the year 2018.

The main aim of this research effort is to assess the impact of the different circulating vehicle fleets on PM10 pollution, comparing the results from the ten most populated metropolitan cities in Italy. Circulating diesel vehicles have been categorized in different groups depending on the vehicle type (car or Light Commercial Vehicle - LCV) and European emission standard. The annual mileage and the total PM10 emission for each category has been determined based on several data sources. Estimated overall annual emissions of PM10 particles have been compared with PM10 concentration measurements from distributed ground monitoring stations. A new index, named SoP (Strength of Pollution), has been defined in order to quantify the contribution of each fleet category to the overall PM10 pollution. The index has been computed for the ten most populated Italian metropolitan cities, i.e. all cities with more than 300.000 inhabits: Rome, Milan, Naples, Turin, Palermo, Genoa, Bologna, Florence, Bari and Catania. Results in terms of SoP estimates for year 2018 reveal the presence in these Italian cities of emission clusters with heterogeneous characteristics, which impose the adoption of different PM10 pollution mitigation approaches in the different cities. For example, in Naples, Catania and Palermo, Euro 0 car fleets emit a total PM10 mass which is respectively 19, 10 and 5 times the mass emitted by Euro 6 vehicles, and consequently a reduction of this fleet is desirable for pollution mitigation purposes. Conversely, in Rome, Genoa and Bari, Euro 3 and 4 car fleets emit a total PM10 mass which is 3-6 times the one emitted by Euro 6 vehicles, which calls for a reduction of these fleets. Thus, the extension to the entire national territory of the results obtained in a specific metropolitan city may be strongly misleading and produce limited effects in terms of pollution mitigation.