Improvement of NOAA NAQFC ozone nighttime over-predictions through offline coupling system of FV3GFS/CMAQ

Meteorological inputs are crucial to improve air quality predictions. The NOAA National Air Quality Forecasting Capability (NAQFC) is an off-line coupling forecasting system, consisting of the EPA Community Multiscale Air Quality (CMAQ) model driven by the NOAA National Centers for Environmental Prediction (NCEP) regional operational weather forecasting model, the Non-hydrostatic Multi-scale Model on the Arakawa staggered B-grid (NMMB). Currently the NAQFC provides numerical guidance for surface ozone (O₃) and particulate matters with a diameter of 2.5 micrometers or less (PM_2,5) forecast for the country. However, the over-prediction of surface ozone by the NAQFC has been an ongoing bias of this system for many years. In this study, the CMAQ model is recoupled with the Finite Volume Cubed-Sphere (FV3) core based Global Forecasting System (GFS) in an offline mode. The interface coupler for meteorology and air quality models is revisited for mapping the FV3GFS outputs from the longitude and latitude grids and hybrid vertical levels of FV3GFS to the C-grid and sigma levels of CMAQ. The FV3GFS/CMAQ predictions of surface O₃ and PM_2.5 are compared with current operational products and evaluated with the USEPA AirNow observational data for one winter and one summer months. The results indicate that ozone nighttime over-predictions are improved significantly. All the night boundary-layer parameters such as planetary boundary layer (PBL) height and eddy diffusivity coefficient are evaluated with available observational data for better understanding the key meteorological factors causing ozone nighttime over-predictions.