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9 Certification standards that limit smoke emissions, as approve the action, it must first be shown to conform with measured by smoke number, indirectly influence aircraft PM the state implementation plan, the state's plan for assuring emissions since smoke is a component of total PM. Limits compliance with the health-based air quality standards. Con- for oxides of nitrogen (NOx) from jet engines have also been formity requires the federal agency to show that the project established. These limit the amount of NOx emitted, which will not create a new exceedance of the standard or exacerbate can produce nitrates that condense in the atmosphere hours any existing exceedances. The FAA must demonstrate con- to days after emissions contributing to secondary volatile formity at airports located in a maintenance or nonattainment particles. area for PM10 or PM2.5. Sulfur emissions are directly related to the sulfur content of the fuel. Internationally accepted standards for Jet A (ASTM D 1.5 What Are the Most 1655-04a May 2005), which is the commercial aviation fuel Recent Aviation PM used in the United States, limit fuel sulfur content to 0.30% Research Efforts? weight maximum. In practice, however, Jet A sulfur content ranges between 0.04 and 0.06% weight (Penner et al. 1999), To remedy the lack of information about PM emissions although lower sulfur jet fuels are now sometimes being seen from aircraft, several initiatives have been pursued in the last as diesel fuel sulfur levels drop. few years. The FAA developed the First Order Approximation Nonroad diesel equipment, such as GSE, are not required (FOA), initially in 2002, as an approach to estimate emissions to have emission controls like diesel vehicles licensed for on- based on smoke number, a measure of soot obscuration in road use. Under new national regulations, EPA requires diesel aircraft plumes. Recently, NASA, EPA, FAA, California Air fuel suppliers for nonroad equipment to reduce fuel sulfur Resources Board (CARB), and others funded a series of aircraft content, eventually to the same ultra-low sulfur limits re- engine emission measurement programs known as APEX quired for on-road diesel. This will influence the introduction (Aircraft Particle Emissions eXperiment). The information of advanced emission control technologies for nonroad equip- from the first APEX1 tests, initially published in 2006, is basic, ment, which may be a requirement for these vehicles in the fundamental data on the quantity and characteristics of PM future. Requirements for diesel fuel sulfur limits and engine from a single engine type. The JETS-APEX2 study, from which emission standards are being phased in between now and a report has been released by CARB, and APEX3, from which 2014. Reducing the fuel sulfur content and adding emission a report is to be released soon, cover a range of commercial controls is expected to reduce PM emissions from nonroad engines, but the data are still limited, relative to the entire equipment by 90% (PM is emitted during electricity genera- fleet. This report describes the findings of these emission tion at the power plant, however, utility power production is measurement programs in detail. well controlled compared to internal combustion engines and Another initiative organized to help close the knowledge the net result is fewer PM emissions). GSE using alternative gap on aviation PM emissions is the National PM Roadmap fuels, such as compressed natural gas, propane, or electricity for Aviation, a research collaboration among federal agencies (U.S. EPA Jul 2004), have very little or no PM emissions. (e.g., FAA, NASA, U.S.DOT, the Department of Defense Stationary emission sources at airports include various [DOD], and EPA), universities, aircraft and engine manufac- facilities and equipment like boilers, emergency generators, turers, airports, airlines, and other stakeholders, that organ- incinerators, fire training facilities, fuel storage tanks, and food ized in 2004 to coordinate aviation PM research and leverage preparation. Many of these equipment types require specific limited resources. Recently, the scope of this initiative has operating permits with PM emission limits. Stationary sources been expanded to include other emissions and has been re- typically represent about 1% of PM emissions at airports. named Aircraft Emissions Characterization (AEC) Roadmap. The National Environmental Policy Act of 1969 (NEPA) Recently, ACRP published a study entitled ACRP Report 6: established a policy to protect the quality of the human envi- Research Needs Associated with Particulate Emissions at Air- ronment and requires careful scrutiny of the environmental ports and, now, this report. Such ACRP initiatives help bring impacts of federal actions, which could include grants, loans, needed focus to airport-specific PM emission concerns. leases, permits, and other decisions or actions requiring federal review or approval. For airports, NEPA applies to most major 1.6 Why Are Aviation-Related construction projects as a result of FAA funding or approval. PM Issues Important to Required by NEPA is the consideration of emissions associ- Airport Operators? ated with a project and identification of the project-related effects as being significant if the project would result in an In addition to complying with general conformity require- exceedance of the ambient air quality standards. When un- ments and assisting states in complying with NAAQS, airports dertaking a federal action, before the federal agency can must address complaints from communities and employees

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10 who are concerned about health impacts resulting from to improve our understanding of the contribution of airport exposure to airport emissions. Many airports also receive emissions to deposited PM. Subsequent sections of this re- complaints about deposits of soot, grit, and the oily residue port discuss the movement of PM off the airport and gaseous that airport neighbors find on their cars and outdoor furni- emissions from aircraft engines. ture, which the complainants believe must come from airport As a result of federally funded research programs, PM activity. However, airports have very limited data on PM emissions from a few engine types have been partially char- emissions from aircraft engines and APUs. Data for other acterized, but most engine models in the fleet remain untested. airport sources varies in quality and availability, and only Research results are still being analyzed to better understand limited data are available on ambient PM around airports. PM formation in aircraft engines and its evolution in the Several airports have conducted particle deposition studies plume. More testing will be required to acquire data needed in nearby and adjacent communities near Los Angeles Inter- to develop emission factors related to engine operating con- national Airport (Barbosa et al. 1999; Barbosa et al. 2001; ditions with the same level of confidence as those available for Eden et al. 2000; Venkatesan 1998), Rhode Island's T.F. Green gaseous emissions. Airport (VHB, Inc. 2006), Boston Logan International Airport With regard to GSE, EPA has taken steps to reduce PM (Hoffnagle 1996; KM Chng 1996), Charlotte/Douglas Inter- emissions from nonroad vehicles. In response to national national Airport (Goldman 2005; KM Chng 1998), John environmental regulations, refiners will begin producing low- Wayne-Orange County Airport (Stolzenbach 2001), Seattle- sulfur diesel fuel for use in locomotives, ships, and nonroad Tacoma International Airport (Port of Seattle 1995), Fort equipment, including GSE. Low-sulfur diesel fuel must meet Lauderdale Hollywood International Airport (Suarez et al. a 500 parts per million (ppm) sulfur maximum. This is the 2004; Webb 2006), and Chicago O'Hare International Airport first step of EPA's nonroad diesel rule, with an eventual goal (Goldman 2005; KM Chng 1999). None of these studies have of reducing the sulfur level of fuel for these engines to meet shown a definitive link between the airports and the deposited an ultra-low standard (15 ppm) to encourage the introduction material. These studies commonly find the deposits are typical of new advanced emission-control technologies for engines of the material found throughout urban areas that come from used in locomotives, ships, and other nonroad equipment. diesel trucks, construction activity, wind-blown dust, pollen, These most recent nonroad engine and fuel regulations com- and mold. This is perhaps not unexpected since it was the plement similarly stringent regulations for diesel highway results of the APEX studies that first clearly indicated that trucks and buses and highway diesel fuel for 2007. PM from aircraft is comprised of fine or ultrafine particles, Beginning June 1, 2006, refiners began producing clean which are too small to settle gravitationally or to be deposited ultra-low sulfur diesel fuel, with a sulfur level at or below on stationary surfaces and, thus, remain suspended in the 15 ppm, for use in highway diesel engines. Low-sulfur atmosphere. The studies prior to APEX are not conclusive, (500 ppm) diesel fuel for nonroad diesel engines was required however, since they used different methodologies and many in 2007, followed by ultra-low sulfur diesel fuel for these only sampled dry deposition and did not collect material de- vehicles in 2010 (U.S. EPA May 2004b). Stringent emissions posited through rainfall, which is a primary mechanism for standards for new GSE will be phased in between 2008 and scrubbing suspended particles from the atmosphere. Future 2014 as part of this rule. Whether--and when--similar re- deposition studies will be able to build both on these findings ductions in fuel sulfur content will occur in aviation jet fuel and on new information coming from aircraft PM research has not been determined.