Presentation description

The Salt Lake City area frequently sees summer tropospheric ozone (O3) concentrations that exceed the EPA's standards for "healthy" air quality. O3 is a main component of photochemical smog and can cause inflammation of the lungs, difficulty breathing and increased risk of asthma attacks, bronchitis, and lung infections. Salt Lake City lies near a major mining facility, U.S. Magnesium, that produces of 14% of the world's magnesium for use in metal alloys, batteries, and bombs. This facility emits reactive halogen gases as a by-product of their mining process and is the largest point source of reactive halogen gases in the U.S. The complex role that halogen chemistry plays in the production of tropospheric O3 is not well understood. Therefore, understanding the impact of these halogen emissions on summertime O3 formation is critical in designing effective air quality management strategies in Salt Lake City. It's been well established that O3 is produced in the atmosphere through a complex series of reactions involving the oxidation of Volatile Organic Compounds (VOCs) in the presence of Nitrogen Oxides (NOx). The presence of halogens can lead to an increase in O3 concentrations by increasing downwind NOx and oxidant concentrations (as it does in the wintertime in Salt Lake City) or lead to a decrease in O3 production through catalytic loss cycles (as it does in the stratosphere). In this work, we use NOx, O3, and VOC data collected at Hawthorne Elementary in downtown Salt Lake City as input to an explicit box model containing >15,000 reactions, the Framework for 0-D Atmospheric Modeling (F0AM), to compare predicted O3 concentrations with and without halogens. We find that model predictions of O3 in the region are sensitive to unmeasured reactive halogen concentrations and unmeasured secondarily produced semi-volatile VOC concentrations. Our results underscore the need for better local constraints to decrease uncertainty in predictions of O3 concentrations under future potential emissions scenarios.