EC-15. CU MAX-DOAS Observations of Halogen Emissions at The Great Salt Lake

Abstract
The largest industrial magnesium plant in the United States is located on the western edge of the Great Salt Lake in Utah. US Magnesium LLC mines magnesium chloride (MgCl2) and magnesium bromide (MgBr2) from the Great Salt Lake, extracts the magnesium, and releases large amounts of hydrochloric acid (HCl), chlorine (Cl2), bromine (Br2), and bromine chloride (BrCl) into the atmosphere. In fact, this plant is the largest industrial point source of chlorine emissions in the United States. US Magnesium LLC is only required to report HCl and Cl2 emissions to the Environmental Protection Agency (EPA), while bromine and other halogen emissions go unreported. Because halogen radical chemistry is a driver of secondary ozone and aerosol formation, these magnesium plant emissions significantly impact urban air quality in the Great Salt Lake Basin (GSLB). The plant is currently offline and is scheduled to restart production in the coming months. The plant shutdown provides an opportunity to characterize baseline halogen emissions from the Great Salt Lake, while the plant restart provides an opportunity to characterize halogen emissions from the magnesium plant. Since January 2023, the University of Colorado Multi-Axis Differential Optical Absorption Spectroscopy (CU MAX-DOAS) instrument has been operational on the eastern edge of the Great Salt Lake. The CU MAX-DOAS instrument measures bromine monoxide radical (BrO), chlorine dioxide radical (OClO), formaldehyde (HCHO), nitrogen dioxide radical (NO2), and other species relevant to urban air quality. The goal of this project is to generate a long-term time series of measurements that characterizes the effect of halogen emissions from both the Great Salt Lake and the magnesium plant on urban air quality in the GSLB.