Do emissions from ships have a significant impact on concentrations of nitrogen oxides in the marine boundary layer?

The potential impact of ship emissions on concentrations of nitrogen oxides and reactive nitrogen compounds in the marine boundary layer is assessed u sing a global chemical transport model. The model predicts significant enha ncements of these compounds over large regions, especially over the norther n midlatitude oceans. This result is consistent with a recently published s tudy, though the impacts predicted here are more widespread and the peak en hancements are not as large. However, comparisons of model results with rec ent measurements over the central North Atlantic Ocean do not provide suppo rt for these model predictions. While one cannot completely overlook the po ssibility that emissions of nitrogen oxides from ships may be overestimated , our analysis suggests that there may be a gap in our understanding of the chemical evolution of ship plumes as they mix into the background atmosphe re in the marine boundary layer. On a related note, it is also possible tha t the overestimate of the impacts of ships on nitrogen oxides in the marine boundary layer by global models is due to the lack of parameterized repres entations of plume dynamics and chemistry in these models.