Impact of low-sulfur marine fuel regulations on PM

PM2.5 negatively impacts on human health and results from various domestic and transboundary sources, including shipping emissions. Maritime transport, which relies on heavy fuel oil, is one of the primary sources to air pollution. In response, the new marine fuel regulation (the IMO Sulfur Cap 2020) was introduced to reduce sulfur oxide emissions from ships. This study quantified PM2.5 contributions from maritime transport in the Kyushu region of western Japan. Seasonal PM2.5 chemical composition data from six monitoring sites (2016-2022) were utilized for the Positive Matrix Factorization model. Seven factors were identified: secondary sulfate and biomass burning (49.2%), road transportation (19.3%), heavy oil combustion (8.9%), secondary nitrate (6.6%), coal combustion (6.4%), soil (6.1%), and sea salt (4.8%). Secondary sulfate showed a gradual decrease, reflecting the Chinese governments’ air pollution mitigation measures. In contrast, heavy oil combustion, strongly linked to shipping emissions, exhibited a sharp reduction after 2020. During 2017-2019 and 2020-2022, the contributions decreased by 65-97% across all sites, with the largest declines in Fukuoka and Oita. These results indicate that the IMO Sulfur Cap 2020 significantly reduced ship-related PM2.5 in Kyushu, highlighting the importance of international emission regulations for regional air quality improvement.