VOC identification and inter-comparison from laboratory biomass burning using PTR-MS and PIT-MS

Volatile organic compounds (VOCs) emitted from fires of biomass commonly found in the southeast and southwest U.S. were investigated with PTR-MS and PIT-MS, which are capable of fast measurements of a large number of VOCs. Both instruments were calibrated with gas standards and mass dependent calibration curves are determined. The sensitivity of the PIT-MS linearly increases with mass, because the ion trap mass spectrometer used in PIT-MS is more efficient for higher masses, whereas the quadrupole in PTR-MS is most efficient around 70 amu. The identification of VOCs in the complicated mix of the fire emissions was done by gas chromatographic pre separation and inter-comparison with other instrumentation: GC-MS, FTIR, and NI-PT-CIMS. With these state of the art identification methods only 50-75% of the mass detectable by PTR-MS or PIT-MS could be identified. The amount of identified material was dependent on the type of fuel used and the phase of the burns, more can be identified in the flaming stage of the fire. Compounds with masses above 100 amu contributed the largest fraction of the unidentified mass. Emission ratios with CO for all identified and unidentified compounds were determined. Small oxygenated VOCs had the highest emission ratios of the observed compounds.