International maritime regulation decreases sulfur dioxide but increases nitrogen oxide emissions in the North and Baltic Sea

Sulfur dioxide and nitrogen oxide emissions from shipping have been regulated internationally for more than fifteen years. Emissions reduction from shipping provides benefits for human health and the environment, but the effectiveness of regulations in reducing ship emissions is less well understood. Here, we examine how the establishment of European Emission Control Areas and other international maritime regulations in the North and Baltic Seas affect sulfur dioxide and nitrogen oxide emissions in the region. We combine and analyze more than 110,000 ship plume measurements, inspection results, and satellite data from 2018 to 2022. We find that compliance rates for sulfur emissions are higher near ports than in open waters. However, the regulations did not affect the concentration of nitrogen oxide emissions, which increased in the past three years. These findings highlight the need for enhanced emission regulations that improve air quality. International regulations of ship emissions in the North and Baltic Seas did not reduce nitrogen oxide emissions and limited the reduction of sulfur dioxide emissions mostly close to ports, according to analyses combining emissions measurements, ship inspection results, and satellite data.