Assessing the co-benefits of CO2 mitigation on air pollutants emissions from road vehicles

This paper quantitatively assesses the co-benefits of atmospheric CO2 stabilization at 400ppmv by 2100 on air pollutants emissions from road vehicles using a global energy system model treating the road transport sector in detail. It is estimated that the reduction rate of global cumulative emissions of SO2, NOx, and PM from road vehicles during the period 2020–2100 in the 400ppmv CO2 stabilization scenario compared to the no CO2 constraint scenario is 22.1%, 10.8%, and 14.4%, respectively. Such co-benefits are the largest for SO2 because biomass-derived Fischer–Tropsch products are chosen as a major alternative fuel for road transport in the former scenario and because their SO2 emission factor is zero, whereas their NOx and PM emission factors are lower than those for petroleum products only by 27% and 21%, respectively. This implies that introducing liquid biofuels would not lead to a noticeable reduction in NOx and PM emissions. Such co-benefits are the smallest for NOx. The first reason is that, except for 2100 in the no CO2 constraint scenario, heavy-duty trucks account for the largest share of global road vehicles’ NOx emissions in the two scenarios throughout the time horizon. The second reason is that in each time period, heavy-duty trucks emit almost the same amount of SO2, NOx, and PM between the scenarios because of almost the same technology and fuel choices in this sector. This implies the necessity of promoting R&D for developing cost-effective low-carbon alternatives to diesel heavy-duty trucks to achieve a further reduction in global air pollutants emissions from road vehicles.