ARTICLE International maritime regulation decreases sulfur dioxide but increases nitrogen oxide emissions in the North and Baltic Sea Ward Van Roy 1?, Benjamin Van Roozendael 1, Laurence Vigin 1, Annelore Van Nieuwenhove1, Kobe Scheldeman1, Jean-Baptiste Merveille1, Andreas Weigelt2, Johan Mellqvist 3, Jasper Van Vliet 4, Danielle van Dinther5, Jorg Beecken6, Frederik Tack7, Nicolas Theys7 & Frank Maes8 Sulfur dioxide and nitrogen oxide emissions from shipping have been regulated internationally for more than ?fteen years. Emissions reduction from shipping provides bene?ts 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 ?nd 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 ?ndings highlight the need for enhanced emission regulations that improve air quality. https://doi.org/10.1038/s43247-023-01050-7 OPEN 1 Royal Belgian Institute of Natural Sciences, Vautierstraat 29, 1000 Brussels, Belgium. 2 Federal Maritime and Hydrographic Agency, Bernhard-Nocht-Straße 78, 20359 Hamburg, Germany. 3 Chalmers University of Technology, Hörsalsvägen 11, 412 96 Gothenburg, Sweden. 4Human Environment and Transport Inspectorate, Rijnstraat 8, 2500 The Hague, the Netherlands. 5 TNO Innovation for life, Westerduinweg 3, 1755 LE Petten, the Netherlands. 6 Explicit ApS, Teknikerbyen 5, 2830 Virum, Denmark. 7 Royal Belgian Institute for Space Aeronomy, Ringlaan 3, 1180 Brussels, Belgium. 8Ghent University, Faculty of Law & Criminology, Universiteitstraat 4, 9000 Ghent, Belgium. ?email: wvanroy@naturalsciences.be COMMUNICATIONS EARTH & ENVIRONMENT | (2023) 4:391 | https://doi.org/10.1038/s43247-023-01050-7 | www.nature.com/commsenv 1 12 34 56 78 9 0 () :,;