Estimating Nitrogen Oxides emissions from inland waterway vessels using MAX-DOAS measurements – Results of pioneering measurements and plans to advance the method

Nitrogen oxides (NO_x, i.e. NO and NO₂) are a major contributor to urban air pollution and have negative impacts on human health, relating to respiratory and cardiovascular problems. NO₂ is also a precursor of secondary particulate matter and tropospheric ozone, which are also associated with adverse effects on human health. Inland waterway vessels are a significant source of NO_x emissions due to their diesel engines operating at high temperatures. Emissions from inland ships are concentrated in the vicinity of waterways, and could be a significant local air pollution source, particularly in residential areas located along intensively used waterways, narrow and steep river valleys, and small villages without heavy road traffic or nearby power plants. Hence, quantifying the influence of inland ship emissions on air quality and humans is important.

We demonstrate the use of ground-based MAX-DOAS (Multi AXis-Differential Optical Absorption Spectroscopy) measurements to estimate NO_x emissions from inland ships on the Rhine River in western Germany. We show that this method can be used to derive ship emissions of NO_x for individual plumes and as an average over several plumes. However, we also identify several challenges with this approach and propose ways to improve it.

The combination of MAX-DOAS and in situ measurements, particularly knowledge of the NO/NO₂ ratio could lead to more accurate estimates of ship emissions. In addition, we introduce planned systematic measurements at selected locations, such as narrow parts of the Rhine and Moselle valleys, where ship emissions may be a major pollution source. We plan to apply regional models to estimate the effect of the updated ship emissions on local NO_x concentrations.