Effects of reducing SO2 and NOx emission from ships on air quality in Alaska

We performed simulations with the Alaska-adapted WRF/Chem using the same meteorological conditions of January 2000, but alternatively applying the emissions of 2000 (REF), emissions of 2000 with the ship-emission reductions for the planned North American Emission Contral Area (ECA) for SO2 only (ECA1) and SO2 and NOx (ECA2) that have been proposed by the International Maritime Organization for 2015. The analysis focused on the air quality along the international shipping lanes (ISL), in the ECA and over Alaska (AK). Our goal is to examine how the decreases in ship emissions in the ISL and ECA affect to air quality in Alaska. Our model results show that reducing SO2 and NOx ship-emissions reduces the concentration of sulfur and nitrogen compounds over Alaska despite of no changes in Alaska emissions. The reductions of pollutants over the ISL, ECA and AK stemming from concurrent SO2-NOx ship emission reductions are an order of magnitude of those stemming from SO2 reduction in ship emissions only. Reductions in sulfur compounds reach up to 14km while reductions of nitrogen compounds reach to only about 7km. Reductions of sulfate and nitrate in clouds are highest at the top of the boundary layer. Among the three regions of interest, strongest reductions occur over the ECA and ISL for sulfur and nitrogen compounds, respectively, since the ECA (ISL) has highest reductions of SO2 (NOx). The PM2.5 speciation partitioning over all three regions marginally changes when the ship emissions change. Sulfate is the major component of PM2.5 in all regions. Closer to the land, organic carbon (OC) partitioning is higher indicating the enhancing impacts of inland anthropogenic emissions to total PM2.5 concentrations over land.