Investigation of Ozone Formation Chemistry during the Salt Lake Regional Smoke, Ozone, and Aerosol Study (SAMOZA).

Salt Lake City (SLC), UT, is an urban area where ozone (O) concentrations frequently exceed health standards. This study uses an observationally constrained photochemical box model to investigate the drivers of O production during the Salt Lake Regional Smoke, Ozone, and Aerosol Study (SAMOZA), which took place from August to September 2022 in SLC. During SAMOZA, a suite of volatile organic compounds (VOCs), oxides of nitrogen (NO), and other parameters were measured at the Utah Technical Center, a high-NO site in the urban core. We examined four high-O cases: 4 August and 3, 11, and 12 September, which were classified as a nonsmoky weekday, a weekend day with minimal smoke influence, a smoky weekend day, and a smoky weekday, respectively. The modeled O production on 4 August and 3 September was highly sensitive to VOCs and insensitive to NO reductions of ≤50%. Box model results suggest that the directly emitted formaldehyde contributed to the rapid increase in morning O concentrations on 3 September. Model sensitivity tests for September 11-12 indicated that smoke-emitted VOCs, especially aldehydes, had a much larger impact on O production than NO and/or anthropogenic VOCs. On 11 and 12 September, smoke-emitted VOCs enhanced model-predicted maximum daily 8 h average O concentrations by 21 and 13 parts per billion (ppb), respectively. Overall, our results suggest that regionwide VOC reductions of at least 30-50% or NO reductions of at least 60% are needed to bring SLC into compliance with the national O standard of 70 ppb.