NOx and SO2 are (primarily) local pollutants, and get broken down over time. Cargo ships is a relatively small contributor to greenhouse gases for most items. (

NOx and SO2 are (primarily) local pollutants, and get broken down over time. Cargo ships is a relatively small contributor to greenhouse gases for most items. (I would not be surprised if a few hundred km by truck causes larger greenhouse gas emissions than around-the-world by ship.