Global and regional climate impacts of black carbon and co-emitted species from the on-road diesel sector

Diesel vehicles are a significant source of black carbon (BC) and ozone precursors, which are important contributors to climate warming, degrade air quality and harm human health. Reducing diesel emissions could mitigate near-term climate change with significant co-benefits. This study quantifies the global and regional climate impacts of BC and co-emitted short-lived climate forcers (SLCFs) from present-day on-road diesel vehicles, as well as future impacts following a current legislation emission scenario. Atmospheric concentrations are calculated by the chemical transport model OsloCTM2. The following radiative forcing (RF) and equilibrium surface temperature responses are estimated. For year 2010 on-road diesel emissions we estimate a global-mean direct RF from BC of 44mW/m2 and an equilibrium surface temperature response of 59mK, including the impact of BC deposition on snow. Accounting for cooling and warming impacts of co-emitted SLCFs results in a net global-mean RF and warming of 28mW/m2 and 48mK, respectively. Using the concept of Regional Temperature change Potential (RTP), we find significant geographical differences in the responses to regional emissions. Accounting for the vertical sensitivities of the forcing/response relation amplifies these differences. In terms of individual source regions, emissions in Europe give the largest regional contribution to equilibrium warming caused by year 2010 on-road diesel BC, while Russia is most important for Arctic warming per unit emission. The largest contribution to warming caused by the year 2050 on-road diesel sector is from emissions in South Asia, followed by East Asia and the Middle East. Hence, in regions where current legislation is not sufficient to outweigh the expected growth in activity, accelerated policy implementation is important for further future mitigation