Abstract: Air quality is responsible for 6.7 million premature deaths per year according to the World Health Organization, and it is pointed out as an important sanitary issue worldwide. High concentrations of atmospheric pollutants are observed especially in urban areas, due to the reduced ventilation caused by the urban configuration and to the proximity of anthropogenic emission sources. Road traffic is one of the most important sources of regulated and emerging pollutants, such as fine and ultra-fine particles, nitrogen dioxide and black carbon. However, these pollutants are emitted with different rates depending on the vehicle characteristics, such as the fuel (diesel, petrol, natural gas, electricity), the vehicle category (light-duty vehicle, utility vehicle, motorcycle, heavy-duty vehicle and bus), and the vehicle technology, which imposes different emission limits according to the vehicle manufacturing year. In this sense, urban mobility is a key aspect to determine the total amount of traffic emissions, and choices related to the available modes of transport in a city may have an important role in urban air quality. This study investigates the influence of extreme mobility scenarios on pollutant emissions and concentrations at both the urban background and the street scales. The scenarios aims at understanding the potential impact of five different strategies to change urban mobility, imposing very strong limitations on road traffic, such as adopting (i) a limited electrification of private and commercial vehicles and a shift to soft mobility, (ii) a significant increase in the number of users per car and reduced use of private cars car, (iii) a total electrification of the fleet (Paris-region target for 2030), (iv) limits on private vehicles circulation in specific areas, and (v) the implementation of all these measures simultaneously. For this, the multi-scale model chain CHIMERE-MUNICH is employed to calculate the concentrations of multi-pollutants in the urban background and in the streets, respectively. A special focus is given to emerging pollutants, such as black carbon and ultra-fine particles. Both CHIMERE and MUNICH are coupled with the chemical module SSH-aerosol and use the same traffic emissions and meteorological database, which enables a consistent multi-scale approach. Simulations are performed in Paris during summer 2022. This study shows the potentialities of this multi-scale modeling approach to support public actions aiming to reduce population exposure to atmospheric pollution.

Keywords: Mobility scenarios, traffic emissions, multi-scale modeling, street-level resolution.