- Principal Investigator: Chris Emery (Ramboll Americas Engineering Solutions, Inc.)
- Study Period: July 1, 2024 – September 30, 2025
- Funded by Science for Solutions Research Grant: $98,012
- DAQ Contact: Chris Pennell ([email protected])
In its State Implementation Plan (SIP) for the Northern Wasatch Front (NWF), the Utah Division of Air Quality (UDAQ) tabulates the minor ozone contributions derived from local controllable emissions within the NWF relative to more substantial contributions from regional emissions among neighbor states and foreign sources that are consistently present during exceedance episodes. UDAQ’s findings are consistent with those of the Environmental Protection Agency (EPA) addressing ozone over the western US. Despite a multitude of modeling studies in the peer-reviewed literature that consistently characterize total global background contributions to the western US, only a few specifically assess and confirm the importance of deep vertical transport of global ozone from the middle and upper troposphere. However, those studies have employed relatively coarse resolution (12-50 km) with seasonal and regional perspectives, meaning that they have addressed contributions from large-scale general circulations and perhaps some portion of the largest terrain-induced transport mechanisms. Furthermore, the importance of vertical transport has not been evaluated or quantified specifically for international anthropogenic (IA) ozone arriving in the NWF. Source apportionment modeling reported by UDAQ estimates how much IA ozone arrives in NWF but not its transport path. A mechanistic explanation is needed to understand why western US background ozone is consistently highest over Utah and to describe the specific processes that bring IA ozone into the NWF. Such information would bolster and add weight of evidence elements for any future 179B demonstrations for the area.
Ramboll proposes to directly assess, via high-resolution CAMx modeling, the amount of mid/upper-tropospheric IA ozone that is transported into the NWF. The approach will utilize UDAQ’s SIP modeling platform with source apportionment, which resolves local topography from 1 to 4 km scale over the NWF and Utah, respectively, to characterize daily variations in IA contributions from several different altitude ranges between the surface and the stratosphere. The project will address several topics, including the relative importance among transport pathways; the extent to which high pressure centered over Utah blocks or enhances background ozone entering the area; how the relative strengths of these transporting motions vary in time and modulate inter-daily variations of background ozone; and the extent to which transported peroxyacetyl nitrate (PAN) impacts transported ozone into the NWF. The proposed work addresses the FY 2025 Science for Solutions Research Grant solicitation by targeting two research priorities: (3) Meteorology-Chemistry Coupling, and (1) Summertime Ozone Chemistry and Sources, specifically (f) background ozone. Additional details about USOS can be found on NOAA’s website.