- In May 2004, as part of the Nonroad Diesel Tier 4 Rule, the Environmental Protection Agency finalized new requirements that decrease allowable levels of sulfur in marine diesel fuel by 99 percent. These fuel improvements, which began to take effect in 2007, reduce particulate matter (PM) from new and existing engines.
- In March 2008, the EPA finalized a three-part program that further reduces emissions from marine diesel engines with per-cylinder displacement below 30 liters. These include propulsion engines used on vessels ranging from recreational boats to towboats, tugboats and Great Lake freighters, and auxiliary engines ranging from small generator sets to large generator sets on oceangoing vessels. The rule will cut PM emissions from these engines by as much as 90 percent and nitrogen oxide (NOx) emissions by as much as 80 percent when fully implemented.
- The 2008 final rule includes the first national emission standards for existing commercial marine diesel engines, applying to engines larger than 600 kW when they are remanufactured. The rule also sets Tier 3 emissions standards for newly built engines, with the standards phased in from 2009. Finally, the rule establishes Tier 4 standards for newly built commercial marine diesel engines above 600 kW, based on the application of high-efficiency catalytic aftertreatment technology. The phase-in period for those standards began in 2014.
Environmental Protection Agency