Modelling the air quality impacts of a zero emission zone scenario in the city of Milan

One of the sustainable mobility policies aimed to reduce road traffic emissions in urban areas is the implementation of zero-emission zones (ZEZ) which are areas where only electric vehicles, pedestrians, and cyclists are allowed. The assessment of possible benefit of ZEZ on emissions, air quality and human health can be performed with a dedicated modelling chain. The goal of this work is to simulate a 2030 ZEZ mobility scenario in Milan city centre (Italy), introducing changes to the vehicle fleet composition within the ZEZ, as suggested by the Air Quality and Climate Plan of the municipality. Then we evaluated the benefits in terms of both air quality and citizens’ health. The assessment of the environmental and health effects is done thanks to a modelling suite composed of a road traffic, an emission, a hybrid air quality models, plus a fourth module for human health impacts. In this specific case study, the modelling chain is applied to the metropolitan city of Milan for the reference year 2017 first, and then for two hypothetical mobility scenarios referred to 2030: the temporal evolution of baseline simulation as planned by the NEC (National Emission reduction Commitments) directive and by local emission containment measures (BAS30) and the BAS30 scenario with the implementation of the mobility policy (ZEZ30). The impact of the policy can be inferred by comparing the two scenarios.

Road traffic emission in 2030 are expected to strongly decrease from the 2017 levels (−84% for NOx and −28% for PM2.5). The road traffic emission reduction introduced by the ZEZ30 scenario compared to the BAS30 scenario is high in the model cells contained within the ZEZ area (complete removal of NOx emissions and up to −45% PM2.5), but given the limited area of the ZEZ the citywide reduction of emissions is 2.24% for NOx and 0.91% for PM2.5. NO2 concentrations are expected to decrease of circa 54% inside the city of Milan under the BAS30 scenario compared with 2017 (35% for PM2.5). Again, the reduction introduced by the ZEZ are low and are mostly included within the ZEZ area (maximum 2% and 0.6 % for NO2 and PM2.5 respectively). Considering the ZEZ30 scenario, morbidity and mortality indicators are expected to decrease of 50% circa compared with 2017. In conclusion, the introduction of the ZEZ in 2030 is expected to have a marginal effect compared to the BAS30 scenario due to the limited spatial extent of the simulated ZEZ, the limited effect of electric vehicles on non-exhaust emissions, and the already strong emission reductions achieved using the projected 2030 vehicle fleet.