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8 United States and 5 to 11 g/m3 in the eastern United States; requirement for these vehicles in the future. These require- for PM2.5, estimates range from 1 to 4 g/m3 in the west to 2 to ments for diesel fuel sulfur limits and engine emission stan- 5 g/m3 in the east. Particulate matter emissions from airport dards are being phased in between now and 2014. Reducing the and other regional sources mix relatively quickly with the fuel sulfur content and adding emission controls will reduce ambient background PM. The combination of emissions PM emissions from nonroad equipment by 90%.8 GSE using from airports and other regional sources and ambient con- alternative fuels such as compressed natural gas, propane, or centrations of PM result in a combined atmospheric PM electricity9 have very little or no PM emissions. loading that depends on complex, nonlinear atmospheric Stationary emission sources at airports include various processes, including chemical reactions and pollution trans- facilities and equipment like boilers, emergency generators, port. This makes it difficult to isolate the contribution of air- incinerators, fire training facilities, and fuel storage tanks. port activity from all other emissions sources in an area. Many of these equipment types require specific operating In addition to the NAAQS, there are other regulations that permits with PM emission limits. Stationary sources typically directly or indirectly effect PM emissions from aviation. For represent about 1% of PM emissions at airports. example, the International Civil Aviation Organization The National Environmental Policy Act of 1969 (NEPA) (ICAO) has established aircraft engine certification stan- established a policy to protect the quality of the human envi- dards5 that limit smoke emissions, as measured by "smoke ronment and requires careful scrutiny of the environmental number." Since smoke is a component of total PM, these impacts of federal actions, which could include grants, loans, standards indirectly influence aircraft PM emissions. leases, permits, and other decisions or actions requiring federal The ICAO has also established international certification review or approval. For airports, NEPA applies to most major limits for oxides of nitrogen (NOx) from jet engines. These construction projects as a result of FAA funding or approval. limit the amount of NOx emitted, which can produce nitrates One of the most common assessments used to confirm NEPA that condense in the atmosphere hours to days after emissions compliance for airport projects is "general conformity," which forming secondary volatile particles. The EPA has adopted seeks to ensure that actions approved by the federal govern- ICAO's certification standards as national regulations and ment do not cause increases in emissions that could exceed air FAA in turn monitors and enforces engine certification. quality standards. This serves to indirectly limit increases in Sulfur in jet fuel combines with oxygen from the air dur- ambient PM and other emissions. ing combustion, producing sulfur dioxide (SO2). This SO2 is further oxidized to sulfuric acid after leaving the engine, and What are the Sources of PM eventually all of the fuel sulfur becomes sulfate. A small frac- at an Airport? tion (a few percent or less) of the sulfur converts to sulfate There are many individual PM emission sources at air- before the engine plume disperses, and is considered part of ports. These include the following: the primary particulate matter emissions. The remaining sulfur converts to sulfate hours to days after the emission, Aircraft engines, contributing to secondary particulate matter. Sulfur emis- Aircraft auxiliary power units (APU), sions are directly related to the sulfur content of the fuel. Ground support equipment (GSE), Internationally accepted standards6 for Jet A, which is the Passenger vehicles, commercial aviation fuel used in the United States, limit fuel Tire and brake wear, sulfur content to 0.30% wt. maximum. In practice, however, Stationary power turbines, Jet A sulfur content ranges between 0.04 and 0.06% wt.7 Training fires, Nonroad diesel equipment, such as GSE, is not required to Sand and salt piles, and have emission controls like diesel vehicles licensed for on-road Construction grading and earth moving. use. Under new national regulations, EPA is requiring diesel fuel suppliers for nonroad equipment to reduce fuel sulfur Particulate matter emissions from each of these sources are content, eventually to the same ultra-low sulfur limits required different in terms of size, composition, and rate. Emissions for on-road diesel. This will allow the nonroad equipment to from these sources can be quantified by direct measurement use advanced emission control technologies, which may be a using monitoring equipment or estimated using emission 5 International Civil Aviation Organization, International Standards and Recom- mended Practices, Environmental Protection, Annex 16 to the Convention on 8 Environmental Protection Agency, Office of Transportation and Air Quality, International Civil Aviation, Volume II, Aircraft Engine Emissions. Final Regulatory Analysis: Control of Emissions from Non-Road Diesel Engines, 6 ASTM International D 1655-04a, Standard Specification for Aviation Turbine EPA420-R-04-007, May 2004. Fuels. 9 PM is emitted during electricity generation at the power plant; however, utility 7 Intergovernmental Panel on Climate Change, Aviation and the Global Atmo- power production is well controlled compared to internal combustion engines sphere (1999). and the net result is fewer PM emissions.