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OCR for page 19
19 CHAPTER 6 Particulate Matter From Other Airport Sources In addition to the airplane engines, aircraft can also emit The EPA's standards for on-road vehicles apply to ground PM from other on-board sources. These other aircraft access vehicles. Emission factors from on-road vehicles are sources include auxiliary power units (APUs) and aircraft estimated by using EPA's MOBILE 6 model. Fleet charac- brake and tire emissions during touchdown. Beyond the teristics such as vehicle mix and age, as well as operating airplanes themselves, other sources also abound at any cycles, are well defined and embedded in the MOBILE given airport, including ground support equipment (GSE) model. and a wide range of airport facility equipment for power Most ground access vehicles are fueled with gasoline, generation, cooking, international waste incineration, which produces very little PM. construction, and so forth. Vehicles bringing passengers, For ground access vehicles fueled with diesel, ultra-low freight, and equipment and supplies can also contribute to sulfur diesel fuel is being phased in and diesel particulate emissions associated with airport operations, and thus filters will be required for on-road use. This will substan- the sources associated with all of the roadside transport ac- tially reduce PM emissions from diesel-fueled ground tivity must also be accounted for when quantifying PM access vehicles. emissions. Airport facility equipment emissions are often defined by EPA standards. Emission factors for stationary sources can be found in a variety of sources, most commonly from Knowledge AP-4222 and Air Quality Procedures for Civilian Airports and Particles in GSE exhaust are well characterized, especially Air Force Bases (The Air Quality Handbook).23 Emission with respect to mass, since the engines used in GSE are the factors for most common stationary equipment at airports same as those found in vehicles in construction, industrial, are contained in EDMS. and commercial applications as well as in on-road vehicles. The GSE equipment market is too small for purpose-built Gaps engines so production engines from manufacturers are used. Particulate matter testing, measurement, and charac- GSE operational practices are not well characterized. GSE terization conducted by EPA and others effectively describe spend much of their operational time idling and only lim- the particles found in GSE exhaust. ited periods under load. For example, a baggage tug may The EPA's emission standards for nonroad equipment apply be idling while awaiting the arrival of an aircraft at a gate. to GSE. Emission factors for these vehicles are estimated by It is then positioned adjacent to the aircraft where it sits at using EPA's NONROAD model. idle. Once bags are loaded on or unloaded from the air- Federal regulations requiring the use of ultra-low sulfur craft, the tug moves back to the terminal area and may sit diesel in nonroad equipment are being phased in and will at idle. Operating practices vary considerably from airport apply to GSE. These regulations will significantly reduce to airport. PM emissions from GSE. Diesel particulate filters are available for use on equipment fueled with ultra-low sulfur diesel which, when combined 22 Environmental Protection Agency, AP 42, Compilation of Air Pollutant Emis- sion Factors, with the fuel sulfur reduction, can result in a 90% reduc- 23 Federal Aviation Administration, United States Air Force, Air Quality Proce- tion in PM emissions. dures for Civilian Airports & Air Force Bases, April 1997.

OCR for page 19
20 Populations and age, which are needed to reliably quantify There is currently no data on PM number, size, and mass GSE emissions, are often difficult to determine. Many air- for brake and tire emissions from landing aircraft. LIDAR port environmental studies use estimates of number of ve- data collected in the UK suggest that this could be a signif- hicles and engine run time needed to service an aircraft; icant PM source at airports. While it is evident that aircraft however, these estimates are not well documented and leave a great deal of rubber on the runway in the vicinity of again vary considerably from airport to airport. This lack touchdown, it is also evident that a puff of smoke or par- of consistent, reliable GSE emission estimation procedures ticulate matter is created during touchdown. is reflected in the variation seen in airport emission inven- The relationships between aircraft brake and tire emissions tories, where GSE PM emissions can vary from less than and brake and tire emissions from roadside vehicles (and 15% to more than 50% of the inventory total. GSE) are not well defined; however, their use would not be Minimal PM data are available for APU emissions. APUs are expected to cause similar brake and tire wear compared to essentially small jet engines and it is expected their emissions landing aircraft. The materials and usage patterns are also would be similar to those of the aircraft main engines; how- quite different for aircraft and road vehicles. ever, APU have different operating cycles. They typically The contribution to airport PM inventories from aircraft operate at three power settings: no load, environmental brakes and tires is highly uncertain at present. control condition,24 and engine start condition.25 The level of detail on PM emissions in nonaircraft-engine Fuel consumption for APUs is unknown, however, they emission sources is not commensurate with that being use much less fuel than the main aircraft engines, and their acquired for aircraft. While number, size, mass, and com- emissions are expected to be proportionately less. position as a function of engine operating condition is For the purpose of developing PM inventories, lack of being acquired for aircraft engines, often average numbers knowledge on APU usage (duration and rate), even once are used for other emissions sources. Understanding num- PM emissions data might become available, remains a gap. ber, size, and composition may be less important for All gaps for aircraft engine PM, both nonvolatile and compiling emission inventories than for understanding the volatile, also apply to APUs since very little PM measure- health effects of these PM sources. ment work has been performed on APUs. Due to various data limitations, we currently lack a means The magnitude of the contribution to airport PM invento- to estimate the relative contributions from aircraft and other ries from APU's use is currently highly uncertain although PM sources to airport PM inventories that reflect actual, expected to be relatively small. source-specific PM data and source operational procedures. Where airport PM inventories have been reported, it is not clear that consistent, reliable methodologies, equipment 24 This is an intermediate power level needed to maintain the aircraft cabin's envi- ronmental control system including the air conditioning and ventilation system. counts, and appropriate operating cycles were used for each 25 This is essentially maximum power needed to start the main aircraft engines. emissions source.