A New Compact Portable Field Instrument for Continuous Real-Time Measurement of Trace Organic Air Pollution Emissions Using Jet-REMPI Mass Spectrometry

The goal of this research project is to develop a compact portable instrument for the measurement of trace hydrocarbon vapors with high sensitivity and high chemical selectivity using the jet-resonance enhanced multiphoton ionization (jet-REMPI) technique. This technology already has been proven to be highly effective for the real-time measurement of complex mixtures of hydrocarbon vapors in the laboratory, but to date has required both a large time-of-flight mass spectrometer and a large, complex, and delicate high-resolution tunable ultraviolet (UV) laser system. By reducing the size and increasing the ruggedness of both the laser and mass spectrometer components, as well as constructing a rugged instrument package, OPOTEK, Inc., plans to deploy a field-portable instrument package for the first demonstration of the technology outside of the laboratory. Phase I bench tests demonstrated that a very strong performance can be obtained utilizing a compact tunable UV laser system component. As the first step in miniaturizing the jet-REMPI instrument, detection sensitivities in the 200-500 ppt range were obtained for a variety of small aromatic compounds, including the benzene, toluene, ethylbenzene, and xylene family. In addition, high chemical specificity was demonstrated in complex mixtures, including the ability to resolve isomers. During Phase II, the system will be further miniaturized by incorporating a compact mass spectrometer. A prototype field instrument will be constructed combining the laser, mass spectrometer, and all support hardware in a compact portable instrument. This instrument will be tested both in the laboratory and at field sites. The performance specifications for this prototype system make it ideal for a number of applications in which real-time field measurements are required, eliminating the need for lengthy sample preconcentration or chromatographic separation. These include real-time monitoring of the time-varying concentration of hazardous air pollutants in urban air, monitoring emissions in real time from both mobile and stationary sources, and rapid mapping of pollutant special distributions. The real-time data obtainable from the instrument also will be ideal for industrial process management, allowing continuous optimization of process parameters for peak efficiency. The technique particularly is powerful for industrial applications because measurements are rapid (several seconds). The instrument can make sensitive measurements even in the presence of high levels of contaminants. The system can rapidly measure the concentrations of many species without the need for reconfiguration.