W ith a death toll of up to 8.8 million premature deathsper year, anthropogenic air pollution has been iden-ti?ed as the global leading cause of death1,2. Air pol- lution from ocean-going vessels (OGVs) is one of the main sources of air pollution. So?ev et al. have calculated that up to 800,000 of these premature deaths can be attributed to OGVs3. These are mainly caused by ?ne particulate matter known as PM2.5.This PM2.5 can be generated during the combustion pro- cess; however, a substantial amount of secondary PM2.5 is also formed from other pollutants like sulfur oxides (SOx), nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs)3–7. Air pollutants from OGVs—SOx, NOx, Ozone (O3) and VOCs—also have direct adverse effects on human health and the environment. In 2014, OGVs were responsible for 13% and 14% of global anthropogenic emissions of SO2 and NOx, respectively8–13. The regulations put in place to reduce emissions from OGVs fall under the MARPOL Convention of the IMO14. Annex VI of the revised MARPOL Convention aims for a gradual decrease of global air pollution by SOx and NOx from OGVs15 (Supple- mentary Notes 1). In addition, MARPOL Annex VI introduced ECAs with tighter emissions standards (Supplementary Fig. 1A–C) and is rati?ed by 105 countries representing 96.81% of the gross tonnage of the world merchant ?eet16–20. According to the International Maritime Organization (IMO), thanks to the establishment of Emission Control Areas (ECAs) and the stricter SO2 emission limits in 2015, SO2 emissions fell by 28.6% between 2014 and 2017, while NOx reported a 1.2% increase over the same period12. So?ev et al. have estimated that before the strengthening of the global sulfur emission regulations for OGVs in 2020, SO2 and sulfur-related particles in OGV emissions were responsible for up to 403,300 premature deaths a year and 14 million cases of childhood asthma3. With the introduction of global emission regulations for OGVs, it was estimated that 263,300 premature deaths (?33%) and 7.6 million cases of childhood asthma (?54%) could be avoided3,4. When concerning NOx, the health bene?ts of introducing NOx emission regulations are not immediately observed as new emission abatement technology needs to be introduced to be compliant with the de?ned emission limits of the regulations. The compliance rate is therefore linked to the scrapping rate, i.e., the rate at which old OGVs are scrapped and replaced by new OGVs as well as the engine overhaul rate, i.e., the rate at which old engines are replaced by new engines with lower emission limits9. Zhang et al. have estimated that the application of the latest introduced Tier III NOx emission standards is the most advan- tageous approach to further reduce the detrimental impact of shipping on human health, as it would reduce up to 36,400 premature deaths per year4. The recently completed EU-funded Shipping Contributions to Inland Pollution Push for the Enfor- cement of Regulations (SCIPPER) project also recommended the establishment of further NOx Emission Control Areas (NECAs)21. It should be highlighted that in order to attain the afore-mentioned health bene?ts a high compliance rate of international emission standards for OGVs needs to be reached. Despite the fact that the abovementioned publications pro- jected important health bene?ts from the implementation of international maritime emission regulations and that emissions models predict a decrease in air pollution from shipping22,23, there still remains a research gap regarding the effectiveness of the established international regulations in reducing real-world emissions from OGVs in the wider ECAs. At the national level, Van Roy et al. showed varying results of the success of interna- tional regulations to improve air quality in Belgium24. The main objective of this article is therefore to examine the effects of the implementation of the European ECAs and other international maritime regulations in the wider North Sea and the Baltic Sea on OGVs’ emissions. This is accomplished in a three- step approach. As a ?rst step, the effects of international emis- sions regulations in the Bonn Agreement (BA) area (North Sea and North-East Atlantic area) (Supplementary Fig. 2) are exam- ined. This was done by analyzing compliance rates based on more than 100,000 remote OGV emission measurements (Supple- mentary Table 2) collected by the BA Contracting Parties (CPs) using in-situ air quality (sniffer) sensors (Supplementary Meth- ods 1). In the second step, data on (1) emission violations and penalties for the BA; and (2) overall port inspection results for the entire EU were examined. In the third step, satellite data for the years 2018–2022 was used to assess any changes in the atmo- spheric concentrations of SO2 and NO2 in the European ECAs. The presented work reveals that international regulations on fuel sulfur content (FSC) are well enforced by the BA Parties and by extension by the entire EU. Compliance rates are well under control and the results of this study show that SO2 non- compliance has reduced substantially since the introduction of the global sulfur cap. The number of recorded infringements in BA and EU ports follows a similar trend. Based on satellite data it was found that atmospheric SO2 concentrations inside the ECA have decreased since the introduction of the global sulfur cap. In contrast, this article demonstrates that NOx emission regulations are less successful, with NOx emissions from OGVs even increasing. Results Regionwide analysis of the remote monitoring data. Non- compliance data from all remote measurement stations and deployments was collected based on three different cutoff levels. This allows the assessment of the severity of the non-compliance behavior in addition to a temporal and spatial non-compliance trend analysis. For the main results, the 0.15% FSC cutoff level was used. Temporal sulfur compliance trends. A decreasing trend in FSC non-compliance rates was observed across all measurement locations within the European Sulfur Emission Control Area (SECA) regions. The non-compliance rate decreased from 7.1 to 0.7%, with an average non-compliance rate of 1.5% when a 0.15% FSC cutoff level is used (Fig. 1). The pattern is similar for the other cutoff levels (Supplementary Fig. 3A, B). Following the implementation of the global sulfur cap in 2020, the non- compliance rates reached their lowest point, with an average non- compliance rate of 0.6%. It is important to acknowledge that the implementation of the sulfur cap in 2020 coincided with the global COVID-19 pandemic, which led to reduced fuel prices25,26. Additionally, several monitoring operations observed a slight increase in non-compliance, starting in 2022. This increase can be attributed to the rise in marine fuel prices resulting from the Russian invasion of Ukraine and the subsequent global price in?ation26. Among the different remote measurement operations applied by the SECA countries, the French measurements with the remote piloted airborne systems (RPAS) exhibited the highest non-compliance rates. The average non-compliance rate was 9.4% and therefore substantially higher than the non-compliance observed by the other remote measurement operations, which varied between 0.1 and 3.7% for the same period. When considering the remote monitoring locations that conducted measurements throughout the entire 2015–2022 period, the Belgian airborne measurements recorded the highest non- compliance rate for the 0.15% FSC cutoff level (5.2%). However, the Danish helicopter measurements displayed the highest non- compliance rate for the 0.13% FSC cutoff level (8.5%). This ARTICLE COMMUNICATIONS EARTH & ENVIRONMENT | https://doi.org/10.1038/s43247-023-01050-7 2 COMMUNICATIONS EARTH & ENVIRONMENT | (2023) 4:391 | https://doi.org/10.1038/s43247-023-01050-7 | www.nature.com/commsenv