The Department of Defense (DoD) has a need to compile emission factor information to identify potential sources of air toxic compounds that may be contributing to ambient air toxic levels. This information would allow DoD to address air permits and emissions reporting questions and enable DoD to employ methods to minimize disruption of training and operational activities through the adoption of preventive operational modes or equipment substitution. Given the limited information available on source air toxics, primarily due to lack of automated methods, innovative approaches are needed to achieve these ends.
The objective of this project was to provide emission factor information on DoD air toxic sources through combined ambient and source-specific air toxic sampling using state-of-the-art trace pollutant detection technologies. These sampling results can be used to understand what impact, if any, DoD sources have on ambient air toxic levels and what operational modes contribute disproportionately to these emissions.
The project objective was approached through the applied development of a combination of three unique, versatile, field-ready, real- and near real-time monitoring techniques that can measure trace air toxic levels: resonance enhanced multi photon ionization time-of-flight mass spectrometry (REMPI-TOFMS) for organic air toxics, laser induced breakdown spectroscopy (LIBS) for metallic air toxics, and optical remote sensing (ORS) methods for verification and measurement of criteria pollutants and other hazardous air pollutants (HAPs). Conventional emission measurements were used for verification of the real-time monitoring results and assessment of their accuracy. A fast sampling method that separates particles from gases was successfully integrated in an overall sampling scheme designed to conserve the integrity of the sample and avoid any particle/gas partitioning, while bringing the quantity of target compounds above the detection limit of the REMPI-TOFMS measurement technique.
The initial source sampling effort was focused on mobile source toxics, particularly off-road vehicles, and subsequent testing targeted sources such as a diesel engine/generator set, aerospace ground equipment, an industrial boiler, and idling aircraft. Mobile sources were characterized by conventional sampling and chassis dynamometer-based sampling as well as, where practical, on-road sampling via conventional and unique modal analyses and measurements. Additional sources, such as jet aircraft engines that idle on a runway, were measured in the later stages of the project.
This project tested three real- and near real-time monitoring techniques to develop air toxic emission factors for DoD weapons platform sources. LIBS was tested and applied solely to the U.S. Marine Corps (USMC) diesel generator. However, the high detection limits of LIBS for toxic metals limited its usefulness as a real-time analyzer for most DoD sources. ORS was tested on a U.S. Air Force auxiliary power unit (APU) with satisfactory results for non-condensable combustion products [carbon monoxide (CO), carbon dioxide (CO2)], but with limited success on condensable volatile organic by-products. A large laboratory-scale REMPI-TOFMS system was first verified on a USMC diesel generator. The results were successfully compared to measurements obtained by conventional certified EPA methods and validated the system as responsive and functional with complex mixtures. A compact, field-ready version of REMPI-TOFMS then was developed for measuring air pollutants in harsh environments such as the exhausts from Humvees, M1 Abrams and Bradley track vehicles, a shipyard waste combustor, and jet engine exhausts. The field tests of the compact REMPI-TOFMS successfully demonstrated the ability to measure real-time air toxic emissions, including polycyclic aromatic hydrocarbons, chlorinated dioxins, and higher chlorinated benzenes, with a high degree of accuracy and precision.
DoD will benefit from understanding how its base operations contribute to levels of ambient air toxics, both from a standpoint of being able to minimize impacts of potential operating restrictions as well as understanding how to limit occupational exposures. Source identification and emissions characterization, coupled with an understanding of how specific modes of source sampling lead to emissions, will provide DoD with an effective tool for emission impact minimization.