Objective

Particulate matter (PM) is an Environmental Protection Agency (EPA) designated criteria pollutant regulated by the National Ambient Air Quality Standards (NAAQS) under the Clean Air Act (CAA). In September, 1997, the U.S. EPA revised the PM regulation to include more stringent standards for PM less than 2.5 micrometers (PM_2.5) in diameter. Most health and environmentally harmful PM_2.5 result from the combustion of fossils fuels in stationary (e.g. power plants) and mobile sources, such as aircraft and ground vehicles. Although it has been recognized that Department of Defense (DoD) operations, particularly aircraft, produce significant PM_2.5 emissions, quantification of these has been a tremendous challenge. The high uncertainty in estimates of military aircraft on regional PM_2.5 inventories may cause unnecessary restrictions, resulting in increased operational costs and adverse impacts to the overall mission. For instance, military training could be restricted to certain hours of the day or limited to a few days a week in order to reduce the adverse impact of aircraft operations on local air quality. In addition, state regulators could require that a new weapon system or use of an alternative (non-petroleum derived) fuel within their jurisdiction require assessment of PM_2.5 emissions to ensure that these will not impact the attainment or maintenance designation level of the region. Therefore, the reliable characterization of military aircraft PM emissions is of upmost importance to determine the burden on the local environment.

The overall objective of this program is to demonstrate the performance of several innovative devices to condition aircraft turbine engine exhaust to allow improved characterization of volatile and nonvolatile PM (total number, mass and composition) using conventional instrumentation. Total PM include non-volatile PM, which are emitted at engine exit temperatures and pressures (i.e., soot) and volatile PM, which are formed via gas-to-particle conversion in the atmosphere (i.e., condensed organics and sulfur species). Although challenging, significant progress on methods for characterizing non-volatile PM has been achieved by the Society of Automotive Engineers (SAE) E-31 committee. This will lead to a measurement standard in an Aerospace Recommended Report (ARP) by late 2013. In contrast, with the exception of a position paper by the SAE E-31 committee in 2005, measurement of volatile PM has not been addressed. Characterization of volatile PM is recognized to be extremely difficult due to its unstable thermodynamic state (including susceptibility to condensation in sampling lines), and the high influence of atmospheric conditions on the resulting physical and chemical properties.