In this action, we are establishing an emission control program for new marine diesel engines rated at or above 37 kilowatts. The affected engines are used for propulsion and auxiliary purposes in a wide variety of marine applications. The standards for these engines will require substantial reductions in oxides of nitrogen and particulate matter emissions to correspond with the next round of emission standards for comparable land-based engines. The standards will lead to significant reduction in oxides of nitrogen and particulate matter emissions from this source. When combined with other mobile source emission control programs, the program described in this action will help provide long-term improvements in air quality in many port cities and other coastal areas. Overall, these emission standards provide much-needed assistance to states facing ozone and particulate air quality problems, which can cause a range of adverse health effects for their residents, especially in terms of respiratory impairment and related illnesses. The persons potentially affected by this action are those who manufacture new marine diesel engines or marine vessels or other equipment using such engines. Additional requirements apply to companies that rebuild or maintain these engines.