Impacts of emission changes on sulfate aerosols in Alaska

WRF/Chem simulations were performed using the meteorological conditions of January 2000 and alternatively the emissions of January 1990 and 2000 to examine whether increases in emissions may have caused the increasing trends in observed sulfate-aerosol concentrations at coastal Alaska sites. The analysis focused on six regions in Alaska that are exposed differently to the main emission sources. Meteorological observations at 59 sites and aerosol measurements at three sites showed that WRF/Chem captured the meteorological situation over Alaska well and simulated the aerosol concentrations acceptably. Except for the region adjacent to the Arctic Ocean that is influenced by local SO2-emissions, Alaska SO2 and SO42−-aerosol distributions are affected by long-range transport of SO2 from ship emissions and/or emissions in Canada and southern Siberia. Local changes in emissions between 1990 and 2000 are not the main cause for concentrations changes in the six regions. The increases of SO42−-aerosols and SO42−-in-cloud along the Gulf of Alaska are caused by increased ship or Canadian emissions. The study provides evidence that the increased ship and Canadian emissions during the last decades can cause increases in sulfate aerosols.