Upgrade the Chemistry Component of the Next Generation Regional Air Quality Forecast System: UFS-AQM

NOAA’s next generation regional air quality model (AQM) forecast system is constructed within the coupling of the Unified Forecast System (UFS) framework, incorporating the chemical core from the Environmental Protection Agency (EPA)’s Community Multiscale Air Quality (CMAQ). In this system, CMAQ is integrated as a column model to solve gas and aerosol chemistry while the transport of chemical species is processed by the Finite Volume Cubed-Sphere Dynamic Core (FV3) and the Common Community Physics Package (CCPP) under UFS. The current chemical mechanism used in the UFS-AQM system is the Carbon Bond 6 revision 3 gas chemical mechanism and the 6^th generation aerosol module (cb6r3_aero6), as introduced by CMAQ v5.2. With the release of the CMAQ v5.4, a new chemistry mechanism, cb6r5_aero7, is available accompanied by various other scientific changes (https://github.com/USEPA/CMAQ). Besides the scientific upgrades, additional structural updates are also needed to accommodate the new features in CMAQ v5.4, such as the Detailed Emissions Scaling Isolation and Diagnostics (DESID) module and the Explicit and Lumped air quality Model Output (ELMO) module. Both historical simulations and near real-time forecasts will be conducted over the current operational modeling domains with a horizontal spacing of 13 km and 64 vertical levels. The model performance on simulating ozone (O₃) and particulate matter with a diameter of less than 2.5 micrometers (PM_2.5) near the surface will be evaluated and compared to the results using the existing UFS-AQM version.