Responses of road traffic emissions and near-surface air pollution under carbon-peaking scenarios

Road traffic emissions exert substantial influences on urban co-control of air pollution and carbon emissions and on near-road population exposure. The main urban area of Shijiazhuang City was selected for a case study, and five scenarios were developed: baseline, energy-efficiency improvement, travel-intensity reduction, structural transition, and current policy. The Long-range Energy Alternatives Planning (LEAP) model was applied to simulate the trends of road traffic CO₂ emissions and representative air pollutants from 2021 to 2045. Under representative meteorological conditions in July 2023, dispersion of traffic-related line sources along major roads within the Second Ring Road was simulated using the CALPUFF model, and inhalation exposure was assessed for different age groups using a daily exposure dose approach. The results show that CO₂ emissions are projected to peak at approximately 10.90 million tonnes in 2040 under the baseline scenario, whereas the current-policy scenario advances the peak to 2030 and reduces it to about 8.91 million tonnes. Distinct source contributions are observed across vehicle categories: light-duty passenger cars dominate emissions of carbon monoxide (CO) and hydrocarbons (HC), while heavy-duty trucks are key contributors to nitrogen oxides (NO_x) and fine particulate matter (PM_2.5). Pollutant concentrations concentrate along arterial-road and expressway corridors and decay rapidly in the lateral direction. Under the current-policy scenario, both near-road concentrations and population exposure decrease overall, with an exposure reduction of approximately 17%-24%. The findings provide quantitative evidence for corridor-specific refined management and coordinated control of air pollution and carbon emissions.