Atmospheric Chemistry Program Seminar

Evaluation of Halogen-Induced Ozone Depletions Near Salt Lake City
Wyndom Chace, ANYL 1st year, CU Boulder
"An unexpected halogen-rich plume, originating from an industrial plant on the western shore of the Great Salt Lake, was sampled on nine separate flights during the NOAA 2017 Utah Winter Fine Particulate Study (UWFPS). Tropospheric ozone depletions were also measured in the halogen plume, analogous to halogen-induced ozone degradation in other regions of the atmosphere such as the arctic troposphere and the stratosphere. This study sought to quantify the halogen flux from the industrial plant and to characterize the photochemical processes that result in tropospheric ozone depletions. The calculated Cl2 and HCl emission fluxes were consistent with the industrial plant’s reported EPA emissions inventory; the inventory does not report fluxes of Br2 and BrCl, which also had significant calculated fluxes. The observed ozone depletions were investigated using a semi-Lagrangian plume setup in a zero-dimensional atmospheric chemistry box model (F0AM). The box model was able to reproduce the magnitude of ozone depletion observed in the daytime January 26 plume (>35 ppbv below background levels) and confirmed that chlorine and bromine radicals, generated from the photolysis of halogen species emitted by the plant, were responsible for the observed ozone depletions. These results suggest that atypical levels of industrial halogen emissions may have significant impacts on local air quality, particularly relevant in the case of this industrial plant due to its close proximity to Salt Lake City."
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An Investigation of Ozone Chemistry During KORUS-AQ Using Observations and Modeling
Lindsey Anderson, ANYL 1st year, CU Boulder
"Ground-level ozone is a toxic air pollutant that is created from reactions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) in the presence of sunlight. The production of ozone is a nonlinear function of its precursors, which complicates emission regulations that target ozone reduction. In this study, ozone chemistry in Seoul, South Korea was investigated using flight observations from the Korea United States Air Quality (KORUS-AQ) field study. Measurements near the city center are characteristic of a highly polluted urban region with high levels of NOx concentration, while measurements to the southwest exhibit high levels of VOC concentration from chemical production facility emissions. The ozone production regime (NOx-limited vs. VOC-limited) in the Seoul Metropolitan Area (SMA) was determined to be VOC-limited, meaning reductions in the concentration of reactive VOCs would lead to a decrease in ozone production. Possible emission reduction regulations were then modeled to understand how they would impact ozone formation in the SMA. It was determined that emission regulations targeting ozone reduction in the SMA should include reductions in both NOx and reactive VOCs because NOx reduction alone would lead to an increase in ozone formation."