The International Maritime Organization (IMO) has progressively tightened global limits on the sulfur content of marine fuels to protect human health and the environment, including by implementing stricter sulfur limits in designated emission control areas (ECAs). Currently, ships must adhere to a global 0.5% fuel sulfur limit and a 0.1% limit in ECAs, unless they use scrubbers. However, studies have found that ships using scrubbers with heavy fuel oil emit more particulate matter and black carbon emissions than those using marine gas oil.

This brief examines how further reducing the global maximum allowable fuel sulfur content from 0.5% to 0.1% could affect air pollution emissions and premature mortality from fine particulate matter (PM2.5). The analysis considers three compliance pathways: a Scrubber Max scenario in which ships that use very-low sulfur fuel oil (VLSFO) switch to high-sulfur heavy fuel oil (HFO) with scrubbers to comply; a Scrubber Allowed scenario in which ships that use VLSFO switch to marine gas oil (MGO) to comply; and a Distillate Only scenario in which scrubbers are not allowed and ships that use HFO and scrubbers or VLSFO switch to MGO to comply.

Relative to a baseline scenario based on 2023 ship activity data, reducing the sulfur content of marine fuels to comply with a 0.1% sulfur limit would:

• Mitigate air pollution. Across the three compliance scenarios, shipping-attributable sulfur oxide emissions are estimated to fall by 75%–85%, PM2.5 by 46%–66%, and black carbon by 27%–41%. The scenario prohibiting scrubbers yields the highest estimated emission reductions.
• Reduce premature deaths. The three compliance scenarios avoid between 3,900 and 4,500 premature deaths annually, with the most significant reductions achieved when scrubbers are not allowed.
• Deliver substantial economic benefits. Health-related economic benefits are estimated to range from $9.3 billion to $10.9 billion annually, depending on the compliance pathway.
• Incentivize cleaner fuels. A global 0.1% sulfur standard that promotes distillate fuel use would increase baseline fossil fuel costs and reduce the price gap between conventional and zero or near-zero greenhouse gas emission fuels.
  Source: International Council on Clean Transportation.