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Statement of Need: Nationwide, emissions from Marine SI engines and Small SI engines contribute significantly to mobile source air pollution. By 2020 without this final rule these engines would account for about 27 percent (1,352,000 tons) of mobile source volatile organic hydrocarbon compounds (VOC) emissions, 31 percent (16,374,000 tons) of mobile source carbon monoxide (CO) emissions, 4 percent (202,000 tons) of mobile source oxides of nitrogen (NOx) emissions, and 16 percent (39,000 tons) of mobile source particulate matter (PM2.5) emissions. The new standards will reduce exposure to these emissions and help avoid a range of adverse health effects associated with ambient ozone, CO, and PM levels. In addition, the new standards will help reduce acute exposure to CO, air toxics, and PM for persons who operate or who work with or are otherwise active in close proximity to these engines. They will also help address other environmental problems associated with Marine SI engines and Small SI engines, such as visibility impairment in our national parks and other wilderness areas. These effects are described in more detail in subsequent sections of this Preamble.

Summary of the Legal Basis: Clean Air Act section 213(a)(1) directs EPA to study emissions from nonroad engines and vehicles to determine, among other things, whether these emissions “cause, or significantly contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Section 213(a)(2) further requires us to determine whether emissions of CO, VOC, and NOx from all nonroad engines significantly contribute to ozone or CO concentrations in more than one nonattainment area. If we determine that emissions from all nonroad engines do contribute significantly to these nonattainment areas, section 213(a) (3) then requires us to establish emission standards for classes or categories of new nonroad engines and vehicles that cause or contribute to such pollution. Specific statutory direction to set standards for nonroad spark-ignition engines comes from section 428(b) of the 2004 Consolidated Appropriations Act, which requires EPA to adopt regulations under the Clean Air Act "that shall contain standards to reduce emissions from new nonroad spark-ignition engines smaller than 50 horsepower."

Alternatives: For Small spark-ignition engines, we considered what is achievable with catalyst technology. Our technology assessment work indicated that the proposed emission standards are feasible in the context of provisions for establishing emission standards prescribed in section 213 of the Clean Air Act. We also considered what can be achieved with larger, more efficient catalysts and improved fuel induction systems. Based on this work we evaluated more stringent HC+NOx standards involving a 50 percent reduction for Class I engines and a 65-70 percent reduction for Class II engines. For Marine SI engines, we considered a more stringent exhaust emission standard for outboard and personal watercraft engines. This second tier of standards could apply starting in 2012 or later. Such a standard would be consistent with currently certified emission levels from a significant number of four-stroke outboard engines. We considered both more and less stringent evaporative emission control alternatives. For small equipment, we considered a less stringent alternative without running loss emission standards. However, we believe that controlling running loss and diffusion emissions from non-handheld equipment is feasible at a relatively low cost. For a more stringent alternative, we considered applying a diurnal emission standard for all small equipment. We believe that passively purging carbon canisters could reduce diurnal emissions by 50 to 60 percent from small equipment. For marine vessels, we considered a less stringent alternative, where there would be no diurnal emission standard for vessels with installed fuel tanks. For a more stringent scenario, we considered a standard that would require boat builders to use an actively purged carbon canister. This means that, when the engine is operating, it would draw air through the canister to purge the canister of stored hydrocarbons.

Anticipated Costs and Benefits: The requirements in this proposed rule would substantially benefit public health and welfare and the environment. We estimate that by 2030, these proposed emission reductions would annually prevent 450 PM-related premature deaths, approximately 500 hospitalizations, and 52,000 work days lost. The total estimated annual benefits of this proposed rule in 2030 would be about $3.4 billion. Estimated costs in 2030 would be many times less at $240 million.

Risks: The health benefits associated with this proposed rule are expressed in terms of avoided premature mortalities and other endpoints, and have been estimated based on scaling of detailed modeling results from EPA's Clean Air Nonroad Diesel regulation.