Use of REMPI–TOFMS for real-time measurement of trace aromatics during operation of aircraft ground equipment

Abstract

Emissions of aromatic air toxics from aircraft ground equipment (AGE) were measured with a resonance enhanced multiphoton ionization–time of flight mass spectrometry (REMPI–TOFMS) system consisting of a pulsed solid state laser for photoionization and a TOFMS for mass discrimination. This instrument was capable of characterizing turbine emissions and the effect of varying load operations on pollutant production. REMPI–TOFMS is capable of high selectivity and low detection limits (part per trillion to part per billion) in real time (1 s resolution). Hazardous air pollutants and criteria pollutants were measured during startups and idle and full load operations. Measurements of compounds such as benzene, toluene, ethylbenzene, xylenes, styrene, and polycyclic aromatic hydrocarbons compared well with standard methods. Startup emissions from the AGE data showed persistent concentrations of pollutants, unlike those from a diesel generator, where a sharp spike in emissions rapidly declined to steady state levels. The time-resolved responses of air toxics concentrations varied significantly by source, complicating efforts to minimize these emissions with common operating prescriptions. The time-resolved measurements showed that pollutant concentrations decline (up to 5×) in a species-specific manner over the course of multiple hours of operation, complicating determination of accurate and precise emission factors via standard extractive sampling. Correlations of air toxic concentrations with more commonly measured pollutants such as CO or PM were poor due to the relatively greater changes in the measured toxics’ concentrations.