Quantification of average NOx emissions from inland ships for different ship types and operation conditions derived from MAX-DOAS measurements

Inland shipping is potentially an important contributor to local air pollution. Long-lasting diesel engines of inland waterway vessels operate at high temperatures and emit NO_x (NO + NO₂), which have negative impacts on human health.  Emissions from inland ships are concentrated near waterways, making their effect on air quality particularly relevant in densely populated regions located along intensively used waterways, such as the Rhine River. Monitoring and quantifying these emissions is necessary for assessing the importance of inland shipping on local air quality besides other emission sources, such as car traffic.

We use MAX-DOAS (Multi AXis-Differential Optical Absorption Spectroscopy) measurements to quantify NO_x emissions from inland ships on the Rhine River in Koblenz, Germany. This remote sensing technique captures ship exhaust plumes from a riverbank while vessels pass the line of sight of the instrument. NO₂ column densities measured at different elevation angles provide information about the vertical NO₂ distribution in and around the plume. Here we present cross-sections of average ship exhaust plumes of NO₂ for different ship types and sizes and for different operation conditions (upstream and downstream) derived from a long-term dataset collected over a period of more than one year. From the combination of the NO₂ plumes and wind data, the corresponding NO_x emissions are estimated.