Midlatitude Ozone Depletion and Air Quality Impacts from Industrial Halogen Emissions in the Great Salt Lake Basin

Abstract

We report aircraft observations of extreme levels of HCl and the dihalogens Cl 2 , Br 2 , and BrCl in an industrial plume near the Great Salt Lake, Utah. Complete depletion of O 3 was observed concurrently with halogen enhancements as a direct result of photochemically produced halogen radicals. Observed fluxes for Cl 2 , HCl, and NO x agreed with facility-reported emissions inventories. Bromine emissions are not required to be reported in the inventory, but are estimated as 173 Mg year −1 Br 2 and 949 Mg year −1 BrCl, representing a major uncounted oxidant source. A zero-dimensional photochemical box model reproduced the observed O 3 depletions and demonstrated that bromine radical cycling was principally responsible for the rapid O 3 depletion. Inclusion of observed halogen emissions in both the box model and a 3D chemical model showed significant increases in oxidants and particulate matter (PM 2.5 ) in the populated regions of the Great Salt Lake Basin, where winter PM 2.5 is among the most severe air quality issues in the U.S. The model shows regional PM 2.5 increases of 10%−25% attributable to this single industrial halogen source, demonstrating the impact of underreported industrial bromine emissions on oxidation sources and air quality within a major urban area of the western U.S.

High Chlorine Concentrations in an Unconventional Oil and Gas Development Region and Impacts on Atmospheric Chemistry

“…This is consistent with the presence of Cl 2 emissions and their subsequent chemistry leading to an increase in ozone formation. While some measurements have shown tropospheric depletion of ozone by chlorine and other halogens, in polluted urban environments, ozone enhancement by chlorine radicals has been previously observed in early morning air masses. ,, …”

“…Reactive chlorine species such as molecular chlorine (Cl 2 ) and nitryl chloride (ClNO 2 ) photolyze in the atmosphere to form chlorine radical (Cl), a potent atmospheric oxidant that impacts air quality by oxidizing VOCs, contributing to the formation of ozone and secondary organic aerosol, and affecting radical budgets. – Cl radical oxidizes a wide range of VOCs, often more rapidly than hydroxyl radical (OH), – and forms a different set of products than other oxidants. , These include organochlorine species (generally formed when Cl adds to a double bond), which may have substantial health impacts. Furthermore, observations and models show that Cl radicals alter OH and O 3 concentrations. – …”

Examining the Summertime Ozone Formation Regime in Southeast Michigan Using MOOSE Ground‐Based HCHO/NO2 Measurements and F0AM Box Model

“…The resulting ozone isopleths were calculated and plotted for determining ozone formation regimes in SEMI. More details on the F0AM model inputs and model configuration can be found in Table S1 in Supporting Information and elsewhere (Coggon et al., 2021; Rickly et al., 2023; Robinson et al., 2021; Souri et al., 2020; Wolfe et al., 2016; Womack et al., 2023).…”

“…A 2‐day averaged profile of O 3 and precursor concentrations was then constructed and input to the F0AM model (hereafter referred to as “average high O 3 conditions”). To account for physical losses of O 3 , a first‐order dilution constant ( k dill ) was tuned to fit the measured concentration of O 3 in each modeled day (Rickly et al., 2023; Womack et al., 2023). The resulting dilution constant determined by the “average high O 3 conditions” was 1.6 × 10 −5 s −1 , which was scaled up and down by 20% and incorporated into model analyses as uncertainty ranges (Rickly et al., 2023; Womack et al., 2023).…”

“…To account for physical losses of O 3 , a first‐order dilution constant ( k dill ) was tuned to fit the measured concentration of O 3 in each modeled day (Rickly et al., 2023; Womack et al., 2023). The resulting dilution constant determined by the “average high O 3 conditions” was 1.6 × 10 −5 s −1 , which was scaled up and down by 20% and incorporated into model analyses as uncertainty ranges (Rickly et al., 2023; Womack et al., 2023). In this analysis, the O 3 chemistry was evaluated for midday (12:00–16:00 local time) when variation in boundary layer height is minimal and thus dilution effects due to boundary layer expansion are negligible (Coggon et al., 2021).…”