Assessing the co-benefits of reductions in mobile-source CO2 and pollutant emissions for urban air quality and public health.

Mobile sources are now primary contributors to carbon-pollutant emissions in urban China, so jointly reducing the CO2 and pollutants they emit is an urgent priority. Clarifying how the coordinated mitigation of carbon/pollution from mobile sources impacts air quality and public health is crucial for optimizing such strategies and enhancing policy effectiveness. Here, we established three co-reduction pathway scenarios for mobile sources in a representative Chinese city (Xi'an) based on national and local policy frameworks. Emission inventories of CO2 and key air pollutants were calculated for the baseline year and projection years, using activity data and emission factors. We then combined the WRF-CMAQ atmospheric model with the BenMAP-CE health model, to quantify the effects of coordinated carbon and pollutant reductions on fine particulate matter (PM2.5) and ozone (O3) concentrations, and to estimate their associated health impacts. Under the "green low-carbon" and "deep low-carbon" pathways, Xi'an's mobile-source CO2 emissions would peak in 2035 and 2030, respectively, with light passenger vehicles and heavy trucks being predominant sources of emissions. Non-road mobile machinery emerged as the paramount contributor to PM2.5, while emissions from tire and road surface wear continually rose during the projection period. Moreover, the air quality improvement process is distinguished by regional inequalities and urban-rural disparities, with resultant health benefits concentrated in urban centers. Compared with the BAU scenario, implementing the deep low-carbon pathway could prevent about 7700 premature deaths in Xi'an by 2035. Our methodology offers a practical, timely reference for policymakers seeking co-reduction strategies in large cities that achieve both air quality improvements and public health benefits.