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Measuring PAHs in Airplane Emissions

In the March 2000 issue of EHP, Joachim D. Pleil and colleagues reported the results of their study of Air Force personnel exposed to JP-8 jet fuel in the form of fuel vapors and exhaust fumes [EHP 108:183-192]. This month, Jeffrey W. Childers of ManTech Environmental Technology in Research Triangle Park, North Carolina, and colleagues (including Pleil) detail their investigation into human exposure to potentially carcinogenic compounds contained in aircraft exhaust and evaluate the use of various instruments for measuring PAH emissions [EHP 108:853-862].

Their study focused on the presence in aircraft exhaust of polycyclic aromatic hydrocarbons (PAHs). Several of these compounds have been listed by the National Toxicology Program as reasonably anticipated to be a human carcinogen, particularly those PAHs associated with the particulate phase, once they've bound to respirable particles. So an accurate measurement of the presence of particle-bound PAHs is critical to assessing the risk of exposure to personnel involved in aircraft support, maintenance, and usage. To be useful in realistically assessing both health risks and the potential need for workers to use respiratory protective equipment during periods of acute exposure, the measurement method must provide data over time, because exhaust levels rise and fall sharply during various activities associated with the aircraft.

In this study, the authors evaluated methodologies for quantifying PAH concentrations in exhaust. The equipment to do so reliably and accurately exists today in the form of integrated-air samplers, which collect PAHs on a filter cartridge. The compounds are then extracted and measured using sophisticated laboratory analysis. However, this method, although scientifically well validated, is time-consuming, labor-intensive, and expensive, and does not provide vital information about real-time exposures or acute exposures during periods of high PAH emissions, such as start-up and shut-down of engines. With those practical limits in mind, the investigators tested three recently developed photoelectric aerosol sensors (PASs)--two desktop monitors and a prototype handheld model--which were designed to measure and record airborne PAH concentrations in real time.

Tests were conducted in a variety of locations during several different flight-related activities over a period of three days at an Air National Guard base in Georgia. In most of the monitoring events, two of each type of PAS were collocated with two integrated-air samplers. The PASs were evaluated by comparing their results to those of the integrated-air samplers.

The comparisons proved to be inconclusive. Due to inherent differences between the instruments, data from the PASs must be calibrated to the values from the air samplers, but a number of limitations made reliable calibration factors between the two types of monitor difficult to establish. For example, the integrated-air samplers are designed to capture both vapor-phase and particle-bound PAHs from ambient or indoor air over periods of 12-24 hours. In this study, the sampling events were much shorter (45-135 minutes), so the amounts of particle-bound PAHs collected by the air samplers were low enough to fall under the devices' method detection limits. On the other hand, the dynamic range of the PASs, which measure only particle-bound PAHs, were often exceeded during the monitoring events--the levels detected by the real-time monitors literally went off the charts, exceeding the range of the instruments. This also served to compromise the accuracy of the calibration factors. The authors concluded that until these calibration issues are ironed out, the real-time PAS monitors can only be used to provide semiquantitative screening estimates of PAH exposure.

But their use as screening tools is important for protection against high exposures. As presently configured, these instruments can provide an immediate warning when PAH concentrations get very high. While overall PAH concentrations were low in the monitored aircraft activities, the extremely high concentrations measured at certain points (such as engine start-up) indicate that for brief periods personnel are at risk of high acute exposure to PAHs, at which times the use of personal protective equipment may be advisable.