The global impact of the transport sector on atmospheric aerosol and climate in the Representative Concentration Pathways

Using the EMAC global climate-chemistry model coupled to the aerosol module MADE, we simulate the impact of land transport, shipping and aviation emissions on global atmospheric aerosol and climate in 2030. Future emissions of short-lived gas and aerosol species follow the four Representative Concentration Pathways (RCPs) designed in support of the IPCC AR5. We compare the resulting 2030 transport-induced aerosol concentrations to the ones obtained for the year 2000 in a previous study with the same model configuration. The simulations suggest that black carbon (BC) and aerosol nitrate are the most relevant pollutants from land transport in 2000 and 2030 and their impacts are characterized by very strong regional variations during this time period. Europe and North America experience a decrease in the land-transport-induced particle pollution, although in these regions this sector remains a major source of surface-level pollution in 2030 under all RCPs. In Southeast Asia, however, a significant increase is simulated, but in this region the surface-level pollution is still controlled by other sources than land transport. Shipping-induced air pollution is mostly due to aerosol sulfate and nitrate, which show opposite trends towards 2030. Sulfate is strongly reduced as a consequence of sulfur reduction policies in ship fuels in force since 2010, while nitrate tends to increase due to the excess of ammonia following the reduction in ammonium sulfate. The continuous growth in air traffic in the future leads to increasing impacts in all scenarios, affecting BC and sulfate concentrations in the northern mid-latitudes at cruise level with some effects also close to the surface. The aerosol-induced climate impact of the transport sectors is dominated by aerosol-cloud effects and, with the exception of aviation, is projected to decrease between 2000 and 2030, nevertheless still contributing a significant radiative forcing to Earth’s radiation budget