Assessing Wintertime Ozone Prediction Sensitivity to Photochemical Mechanism

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  • Principal Investigators: Greg Yarwood (Ramboll), Seth Lyman (Utah State University)
  • Study Period: July 1, 2021 – June 30, 2022
  • Funded by Science for Solutions Research Grant: $98,048
  • DAQ Contact: Nancy Daher (

Ramboll and the Bingham Research Center (BRC) of Utah State University (USU) are pleased to present this proposal in response to the Request for Proposals, “Science for Solutions Research Grant – FY 2022.” This project will be conducted as a collaboration among Ramboll, BRC, and Dr. William Stockwell of the University of Texas at El Paso as an independent sub-contractor. The objective of the study is to thoroughly investigate wintertime ozone prediction sensitivity in the Uinta Basin (UB) among two current photochemical mechanisms using a consistent modeling platform. Recent modeling conducted by BRC using different modeling systems indicates that the Regional Atmospheric Chemistry Mechanism (RACM) produces much higher ozone concentrations than Carbon Bond (CB) mechanisms. Our proposed scope of work will: (1) implement RACM version 2 (RACM2) into the Comprehensive Air quality Model with extensions (CAMx); (2) develop RACM2 photolysis rates for CAMx and emission speciation profiles for the Sparse Matrix Operator Kernel Emissions (SMOKE) processing system; and (3) comprehensively test and understand RACM2 performance in simulating wintertime ozone in the UB relative to the CB version 6 (CB6) mechanism currently implemented in CAMx.

Our proposed project will address one of the goals and priorities defined in the RFP: (VI) Air Quality and Meteorological Model Improvements. Ramboll is the developer of CAMx, which is used throughout the State of Utah to address air quality issues and to provide the technical underpinnings of State Implementation Plans in both UB and the Wasatch Front ozone nonattainment areas. Our proposed project leverages the modeling datasets, insights and experience from BRC’s photochemical modeling research projects addressing wintertime ozone in the UB. Dr. Stockwell is the author of the RACM photochemical mechanism and will serve as technical advisor on implementing RACM2 in CAMx and developing photolysis rates and emission speciation profiles.

Hourly Ozone (ppb) for Ouray and Vernal, 70ppb std