Detection of Ship Fuel Sulfur Contents in Exhaust Plumes at the Kanmon Straits, Japan, before and after the Global Sulfur Limit 2020

The global limit on the sulfur content of ship fuel was reduced from 3.50% to 0.50% in January 2020 to reduce ship emissions of SO₂ and particulate matter. We conducted observational campaigns before and after the new global limit was introduced to detect changes in coastal air quality. We measured ambient concentrations of SO₂ and CO₂ ship plumes on shore with the sniffing method under the Kanmon Bridge over the Kanmon Straits between Honshu and Kyusyu Islands, Japan, for several weeks in August to September in 2019 and 2020. The fuel sulfur content (FSC) estimated from our measurements mainly varied from 0.50% to 3.00% in 2019, whereas the range narrowed to 0.10% to 0.40% in 2020, showing that all the ships complied. The mean FSC in 2020 was reduced to 16% of that in 2019, which was consistent with the reduction in the ambient SO₂ concentration. Sakurai et al.(2021) estimated that after the 2020 global limit was brought in, SO₂ emissions from ships were reduced to 24% of their previous values by assuming that all ships have a FSC of 0.50%. Our results indicate the 2020 global limit led to much greater reductions in SO₂ emissions from ships than expected.