Measurement of Atmospheric Volatile Organic Compounds from Urban, Industrial and Biogenic Sources by Proton-­Transfer Ion Trap Mass Spectrometry

摘要

Volatile organic compounds (VOCs) are released into the atmosphere through a variety of processes. An understanding of the chemistry of VOCs is critical because of their role in air pollution and climate, but their diversity challenges even modern analytical methods. In this work, I present VOC measurements made by Proton-Transfer-Reaction Ion Trap Mass Spectrometry (PIT-MS) in air impacted by different emission sources: biogenic, urban, industrial and biomass burning. The main goal of these studies was to use the PIT-MS instrumentu27s high time resolution, full mass scan capability and capacity for collision-induced dissociation (CID) to quantify complex VOC mixtures. CID was successfully used to identify VOCs and to separate isomeric and isobaric VOCs in biogenic emissions and biomass burning plumes. Comparison of PIT-MS results with other VOC measurement methods, the use of gas chromatography with PIT-MS and CID were all used to characterize the specificity of methods that use proton transfer by H3O+ ions in all four field environments. The results revealed many limitations to common PTR signal attributions. Results from these studies demonstrate the usefulness of the PIT-MS instrument to characterize complex VOC mixtures. In Mexico City, three major sources of VOC emissions were identified: vehicular traffic, liquid propane gas (LPG) usage and chemical formation. VOC emissions relative to carbon monoxide (CO) are about a factor of 2 larger in Mexico City than in the United States. In Houston, TX, PIT-MS measurements were used to evaluate an industrial emissions inventory. The complexity of measured VOCs in industrial plumes is significantly larger than described in the inventory and for many VOCs, emission fluxes inferred from the measurements are significantly higher than those listed in the inventory. Results from these campaigns could inform future inventories and help inform policy decisions. Taken together, PIT-MS instrument is shown to be useful in providing routine, online VOC measurements with clear scientific merit. At the same time, the PIT-MS is successfully used to probe and extend the analytical abilities of proton-transfer-reaction based instruments for atmospheric measurements.