A Modelling Study of the Impact of On-Road Diesel Emissions on Arctic Black Carbon and Solar Radiation Transfer

Market strategies have greatly incentivized the use of diesel engines for land transportation. These engines are responsible for a large fraction of black carbon (BC) emissions in the extra-tropical Northern Hemisphere, with significant effects on both air quality and global climate. In addition to direct radiative forcing, planetary-scale transport of BC to the Arctic region may significantly impact the surface albedo of this region through wet and dry deposition on ice and snow. A sensitivity study is made with the University of L'Aquila climate-chemistry-aerosol model by eliminating on-road diesel emissions of BC (which represent approximately 50% of BC emissions from land transportation). According to the model and using emission scenarios for the year 2000, this would imply an average change in tropopause direct radiative forcing (RF) of -0.054 W center dot m(-2) (globally) and -0.074 W center dot m(-2) over the Arctic region, with a peak of -0.22 W center dot m(-2) during Arctic springtime months. These RF values increase to -0.064, -0.16 and -0.50 W center dot m(-2), respectively, when also taking into account the BC snow-albedo forcing. The calculated BC optical thickness decrease (at lambda = 0.55 mu m) is 0.48 x 10(-3) (globally) and 0.74 x 10(-3) over the Arctic (i.e., 10.5% and 16.5%, respectively), with a peak of 1.3 x 10(-3) during the Arctic springtime.