Global Distribution of Solid Ammonium Sulfate Aerosols and Their Climate Impact Acting as Ice Nuclei

Laboratory experiments show that liquid ammonium sulfate particles effloresce when RHw is below ~34% to become solid and dissolve when RHw is above ~79%. Solid ammonium sulfate aerosols can act as heterogeneous ice nuclei particles (INPs) to form ice particles in deposition mode when the relative humidity over ice is above 120%. In this study we used the coupled IMPACT/CAM5 model to track the efflorescence and deliquescence processes of ammonium sulfate. Results show that about 20% of the total simulated pure sulfate aerosol mass is in the solid state and is mainly distributed in the northern hemisphere from ~50 hPa to ~200 hPa. When these solid ammonium sulfate aerosols are allowed to act as ice nuclei particles, they act to increase the ice water path in the northern hemisphere (NH) and reduce ice water path in the tropics. The addition of these particles leads to a net radiative effect at the TOA ranging from 0.5-0.9 W/m2 depending on the amounts of other ice nuclei particles (e.g., dust, soot) used in the ice nucleation process. The short-term climate feedback shows that the ITCZ shifts northwards and precipitation increases in the northern hemisphere. There is also an average warming of 0.05-0.1 K near the surface (at 2 meter) in the NH which is most obvious in the Arctic region.