Impacts of Boundary Layer Processes On Ozone Concentrations During Salt Lake City 2024 Ozone Campaigns

Existing in-situ and remotely-sensed observations from government agencies and the University of Utah were available along Utah’s Wasatch Front during 2024 to help support the NOAA-sponsored Utah Summer Ozone Study (USOS) and National Science Foundation’s Salt Lake City Summer Ozone Study (SLC-SOS) ozone field campaigns. Salt Lake City’s 2024 summer season will likely be one of the top three summers during the past ten years for ozone exceedance days, with maximum temperatures exceeding 35^oC on 37 days during June-August.

Velocity Volume Processing (VVP) time-height retrievals at high resolution in the boundary layer were derived throughout the summer from the Salt Lake City International Airport Terminal Doppler Weather Radar. In addition to the ten air quality monitoring sites maintained by the Utah Division of Air Quality across Salt Lake and Davis Counties, our group operated additional monitoring sites for surface weather, ozone, and NOx, including a temporary site in the wetlands north of the Airport. Our group also manages the operations of ozone and particulate sensors on 3 light rail cars and 15 electric buses that traverse the Salt Lake City region. We also archive meteorological observations from over a hundred of sites along the Wasatch Front and maintain an extensive multi-year archive of analyses from the operational High Resolution Rapid Refresh modeling system to assess regional conditions, particularly smoke transport from fires throughout the western U.S. and Canada.

Nocturnal drainage flows across the eastern benches of Salt Lake and Davis Counties contributed to transport of moderate background ozone concentrations down into the valleys that competes with urban emission titration along the valley core. Titration was often particularly effective across the wetlands, which are located north of the Airport and west of large refineries. As the downslope and down-valley flows weakened during the morning, ozone concentrations in the northern end of the valley increased. Up-valley and lake breeze circulations then typically transported higher ozone concentrations through the southern end of the valley away from major emission sources. Case studies from 5 and 8 August 2024 will be contrasted using many of the aforementioned existing data resources. During 5 August, higher ozone concentrations tended to build up during the morning near and north of the Airport due to continued southerly flow that was later disrupted by high-based convection. Extensive smoke blanketed the region on 8 August, with the highest ozone concentrations delayed in the southern end of the valley until after 4 PM MDT.