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Air pollutants emitted by ocean-going vessels (OGVs) cause numerous environmental and human health problems. In 2016, the Belgian Coastguard aircraft was equipped with a sniffer sensor to monitor compliance with MARPOL Annex VI Regulation 14. However, the sensor was susceptible to NO and Volatile Organic Compounds (VOCs), which had a negative impact on the measurement uncertainty. The elimination of measurement errors was achieved by modifying the sensor, including among others the addition of a NOx sensor and a custom-designed hydrocarbon kicker. This resulted in a substantial improvement in the measurement quality and uncertainty of the derived Fuel Sulfur Content (FSC). As a direct result of this, the reporting thresholds for non-compliance drastically improved. The data analysis of sampled OGVs showed that compliance levels notably improved between 2019 and 2020 (from 95.9% to 97.3%), coinciding with the implementation of the Global Sulfur Cap. Findings in this study have also demonstrated that OGVs equipped with emission abatement technology (scrubbers) are more susceptible to non-compliance with Regulation 14 of MARPOL Annex VI. Given these results, this article provides an answer to the question of how to monitor effective implementation of NO emissions from OGVs.

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The Royal Belgian Institute of Natural Sciences launched its airborne sniffer program in 2015 whereby a custom-built sniffer sensor was installed onboard the Belgian coastguard aircraft enabling the measurement of SO2 and NOx emitted by ocean-going vessels (OGVs). The data gathered on non-compliant OGVs were subsequently sent to port inspection authorities, who were then able to trigger inspections more rapidly than had they not had the data from the aircraft. This study reveals the added value of airborne alerts on port inspection effectiveness, a subject that had not been previously documented. This article demonstrates that airborne alerts have not only led to increased sanctions but have also drastically improved the efficiency of port inspection authorities, leading to a 50% reduction in the enforcement cost per confirmed violation. Port inspection authorities were able to follow up on 46% of the generated Fuel Sulphur Content (FSC) alerts. Of the alerts that were followed up, 43% were confirmed as non-compliant after inspection. This means that 20% of the total number of generated airborne alerts, which includes those that were not able to be followed up, met conditions for legal sanctioning. In contrast, for NOx alerts, only limited follow-ups were conducted by port inspection authorities. None of the alerts were confirmed with those inspections, mainly due to the lack of inspection mechanisms for real-world NOx emissions under IMO and EU regulations. In addition, for this study, a large-scale remote FSC measurement validation analysis was conducted for the first time, comparing airborne FSC measurements and FSC reference data. In order to obtain FSC reference data, onboard measurements from exhaust gas cleaning systems (EGCSs) were collected, together with fuel samples from Belgian port inspection authorities. The validation analysis revealed that the empiric deviation in the airborne FSC measurements with the FSC reference data was 9%, which was significantly lower than the 25% uncertainty used in the reporting of the alerts. This study helps pave the way for an increased role of airborne monitoring in the MARPOL Annex VI enforcement chain.

Responding to an urgent call for effective and cost-efficient enforcement of emission regulations from ocean-going vessels (OGVs) at sea, the Royal Belgian Institute of Natural Sciences, one of the 17 official partners of the Belgian coastguard structure, launched its airborne sniffer program in 2015. A custom-built sniffer sensor was installed on board of the Belgian coastguard aircraft and has been used for the in-situ measurement of SO2 and NOx in OGV exhausts, providing non-compliance alerts to port inspection authorities in Belgium and other EU member states. To guarantee the consistency in quality and reliability of the airborne non-compliance alerts, the standard operational procedures and measurement methodology have been described and recorded in a sniffer quality management system (SQMS). As part of the SQMS, alerting thresholds for non-compliance with SO2 and NOx standards were defined based on the emission limits and the measurement uncertainty. In addition, compliant measurements for the fuel sulfur content (FSC) were shared through Thetis-EU, which is the sulfur inspection database hosted by the European Maritime Safety Agency (EMSA). By providing both non-compliance alerts and compliant measurements to port inspection authorities, the coastguard aircraft fulfills a first-step in the enforcement chain. This article demonstrates that the reported alerts have not only led to several sanctions, but the analysis also showed that the provision of airborne alerts improved the efficiency of the port inspection authorities drastically, resulting in a cost-efficient improvement of their enforcement strategy. Port inspection authorities were able to follow-up on 46% of the generated FSC alerts. In addition, 43% of the alerted OGVs, which were followed up, were confirmed as non-compliant after a port inspection. Accordingly, conditions were in place to effectively sanction 20% of the non-compliant observations. For NOx alerts, a limited follow-up was done by port inspection authorities and none of the alerts were confirmed by those inspections, which is mainly due to the lack of suitable inspection mechanisms and the absence of additional EU implementation regulations on NOx emission inspections. Aiming at paving the way for a stricter enforcement of airborne non-compliance alerts, a validation analysis was done between the airborne FSC measurements and reference FSC measurements. In addition to onboard measurements from exhaust gas cleaning systems (EGCS), analyzes of fuel samples were also carried out by port inspection authorities in order to acquire reference measurements. The validation analysis presented in this study showed that the empiric deviation of the airborne FSC measurements with the reference measurements was significantly lower than the uncertainty used in the reporting thresholds. It has also been shown that aerial measurements provide evidence-based data that, given an appropriate confidence interval, has the potential to be considered reliable legal evidence.