Impact of ship emissions on marine boundary layer NOx and SO2 distributions over the Pacific basin

The impact of ship emissions on marine boundary layer (MBL) NOx and SO2 lev els over the Pacific Ocean has been explored by comparing predictions (with and without ships) from a global chemical transport model (GCTM) against c ompiled airborne observations of MBL NOx and SO2. For latitudes >15 degrees N, which define that part of the Pacific having the heaviest shipping, this analysis revealed significant model over prediction for NOx and a modest u nder prediction for SO2 when ship emissions were considered. Possible reaso ns for the difference in NOx and SO2 were explored using a full-chemistry b ox model. These results revealed that for an actual plume setting the NO2 l ifetime could be greatly shortened by chemical processes promoted by ship p lume emissions themselves. Similar chemical behavior was not found for SO2.