Carbon monoxide stable isotopes: Extraction technique development and urban atmospheric analysis
PhD: University of Colorado Boulder, 2017.
We have developed an extraction system to analyze isotopes of carbon monoxide (CO). We then analyzed CO isotopes for two years at Indianapolis, IN, USA. These measurements were done at three towers, one of which measured incoming, background air into the city. We quantitatively removed the background signal and determined the urban CO mole fraction and isotopic enhancements. During the winter months, we constrained the isotopic signature and concluded that the majority of CO produced during the winter was produced by fossil fuel combustion. We found that the Indianapolis fossil fuel signature differed from that of studies done in Europe. Further, we performed a limited traffic study to look at CO isotopes from traffic. While this was not conclusive, it did support our hypothesis that a larger fraction of the Indianapolis vehicle fleet may have malfunctioning catalytic systems, which biases the isotopic results, particularly for delta18O
We used the wintertime fossil fuel isotopic signature to help constrain the summertime budget. It was hypothesized that a second source of CO was significant during the summer months. Oxidation of biogenically produced volatile organic compounds (BVOCs) was one possible source. Oxidized BVOCs were consistent with the changes between our winter and summer isotopic source signatures. We then used the isotopic signatures to determine that between zero and sixty percent of the summertime CO budget was produced from oxidized VOCs. This provided the first direct evidence of a larger percentage of urban CO being produced by oxidized VOCs.