| 26 May 2026
Addressing systemic underestimation in global ship emissions from fleet growth and fuel compliance
Abstract. As a hard-to-abate sector, global shipping is under international and regional emission control regulations. To evaluate emission control effects and conduct rapid response air quality simulations, accurate and timely ship emission inventories are indispensable. However, current ship emission inventory models face multiple challenges, including incomplete and delayed global ship fleet description and significant divergence in PM2.5 emissions after global low sulfur regulation came into effect. Here, we established a dynamically updated Ship Emission Inventory Model that allows near-real-time emission calculation. Ship activity and technical database are updated daily instead of yearly to obtain a more complete and rapid description of global ship fleet. Fleet's multiple choices to comply with fuel sulfur regulation were considered, including switching to very low sulfur fuel and utilizing scrubbers to keep consuming heavy fuel oil. The daily expansion of ship technical database uncovered 8% and 6.2% of the total gross tonnage of active bulk carrier and container fleets, unveiling up to 5.4% of global ship CO2 emissions. Without the expansion, the daily underestimation would enlarge over time from about 0.20 Mt CO2/d to 0.29 Mt CO2/d throughout 2024. On the other hand, the single compliance choice assumption and ignorance of heavy fuel oil use after 2020 would lead to underestimation of PM2.5 and BC emissions by approximately 55% and 27%. Although South China Ocean had the most absolute underestimation, the Indian Ocean had the highest underestimated portion, reaching 75% and 39% of its total PM2.5 and BC emissions.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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