Using a global aerosol model adjoint to unravel the footprint of spatially‐distributed emissions on cloud droplet number and cloud albedo

The adjoints of the GEOS‐Chem Chemical Transport Model and a comprehensive cloud droplet parameterization are coupled to study the sensitivity of cloud droplet number concentration ( N d ) over US regions and Central Europe to global emissions of anthropogenic fine mode aerosol precursors. Simulations reveal that the N d over the midwestern and southeastern US is mostly sensitive to SO 2 emissions during August, and to NH 3 emissions during February. Over the western US, N d is mostly sensitivity to SO 2 and primary organic aerosol emissions. In Central Europe, N d is most sensitive to NH 3 and NO x emissions. As expected, local emissions strongly affect N d ; long‐range transport, however, is also important for the western US and Europe. Emissions changes projected for the year 2050 are estimated to have the largest impacts on cloud albedo and N d over Central Europe during August (42% and 82% change, respectively) and western US during February (12% and 36.5% change, respectively).