A reliable and convenient characterization method that provides a detailed hydrocarbon composition profile for transportation fuels is an important part of process optimization directed at reducing regulated emissions. In our previous study (Briker, Y.; Ring, Z.; Iacchelli, A.; McLean, N.; Rahimi P. M.; Fairbridge, C.; Malhotra, R.; Coggiola, M. A.; Young, S. E. Energy Fuels 2001, 15 (1), 23-37) we described the development of a modified gas chromatography, field ionization mass spectrometry method for detailed hydrocarbon type characterization of diesel fuel. The method proved to be an invaluable technique for rapid analysis of diesel fuel. It was less timeconsuming and more informative than the existing mass spectrometry methods, from a characterization point of view, and it was user-friendly and did not require any major modification to an existing commercial instrument, from an instrumentation point of view. This method correlated well with the other methods for total aromatic and saturate groups, and the data for aromatic subgroups were verified against the data obtained from other mass spectrometric and nonmass spectrometric techniques. This paper describes a continuing effort to verify the new GC-FIMS method and produce correlations for the saturate groups. The purpose of this study was to validate GC-FIMS measurements of various saturate types using samples of physically separated fractions, enriched in the individual types by various LC methods described in the literature. In this study, the non-normal paraffinic portion of the saturate fraction of the selected diesel cut was separated into iso-and cycloparaffins. The normal paraffins were quantitatively removed by molecular sieve and additionally determined by high-resolution gas chromatography of the saturate fraction. The contents of iso-and cycloparaffins were calculated gravimetrically in each separated fraction and also analyzed by mass spectrometry methods. The results obtained for the saturate types by different methods were all in good agreement, which demonstrates the applicability of the GC-FIMS method for saturates analysis.

The need for a continuous monitor for environmentally important pollutants at realistic [parts-per-trillion (parts in 10(12))] concentrations measured in real time (minutes) is widely recognized. We developed an instrument that is based on supersonic-jet expansion and cooling, followed by resonantly enhanced multiphoton ionization (REMPI) into a mass spectrometer. This approach furnishes the dual selectivity of narrow-band tuned laser absorption and mass analysis. We initiated a spectroscopic characterization of the jet's collisional cooling behavior to optimize the instrument's sensitivity and selectivity, made measurements of several aromatic compounds (including polychlorinated dioxins) by use of a one-color REMPI scheme, and demonstrated a two-color excitation scheme.

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ABSTRACT. An instrument is described that provides real-time chemical analysis of the composition of individual aerosol particles. A differentially pumped aerosol inlet transfers particles from the ambient atmosphere into the source region of a time-of-ight mass spectrometer where they impact on a heated surface and the resulting vapors are ionized by electron ionization prior to mass analysis. Laboratory calibration studies demonstrated that the instrument was capable of detecting particles with diameters greater than approximately 0.4 m m.The instrument was operated on the NASA DC-8 research aircraft as part of the ( ) 1996 SUbsonic aircraft: Contrail and Cloud Effects Special Study SUCCESS mission with the intent of studying the chemical composition of upper tropospheric particles. More than 25,000 aerosol particle mass spectra were recorded during 19 mission ights. Although approximately 120 of those spectra showed clear evidence of sulfate, nitrate, and other inorganic materials, the remaining spectra contained only mass peaks consistent with water. Moreover, particles were detected only while travers ing clouds. These results are not consistent with expectations of the size, quantity, or composition of upper tropospheric particles. It is likely, however, that a subisokinetic aircraft sampling inlet resulted in the collection of only very large ice particles. This situation would account for both the observed preponderance of water-only spectra and the apparent lack of particles outside of clouds. Despite the sampling problem, the instrument was able to chemically speciate aerosols directly sampled from a medium altitude aircraft. These represent the rst examples of aerosol particles chemically speciated in real time from an airborne platform.