The impact of ship emissions on nitrogen and sulfur deposition in China

A large amount of NO_X and SO₂ emitted from ships may elevate atmospheric N and S and eventually aggravate the deposition of N and S. The understanding of N and S deposition due to ship emissions is still limited, especially for China because it has a long coastline, busy shipping routes, and several large ports. To fill this gap, a comprehensive air quality model was employed in this study to quantify the contributions of ship emissions to N and S deposition on a national scale in China. Both the spatial and temporal variations of N and S deposition, as well as the major N and S species from ship traffic, were investigated. The results indicate that ship emissions contributed significantly to the deposition of N and S, especially in coastal and offshore areas, where the largest ship contribution to both N and S deposition could exceed 15 kg·ha^-1·yr^-1. For N deposition, ship emissions caused an increase in the total N deposition, not only in port areas and along shipping routes but also far inland, with evident seasonal variations. The contribution from dry N deposition was evidently larger than wet N deposition, especially over the coastal areas. S deposition, however, was generally higher along shipping routes but exhibited distinct seasonal variations. The total S deposition was dominated by dry deposition, especially over offshore areas. Ship-caused dry S deposition occurred mainly in offshore areas, while wet S deposition could be found over wider inland regions and inland waterways, although with a markedly smaller magnitude.