Comparison of Meteorological-Chemistry Coupled Online Versus Offline Models in Simulating High Winter Ozone Episode in the Uintah Basin - Utah, USA.

Recent photochemical modeling studies on high winter ozone episodes in the Uintah Basin, Utah have been unsuccessfully in capturing elevated ozone concentration. Discrepancies in emission inventories are considered as the major cause for the underestimation of ozone, however, inaccuracies in simulating meteorological parameters of inversion layers, also play critical roles in the model underperformance. The majority of earlier photochemical models simulate meteorology and chemistry in offline coupling fashion considering no feedback from chemistry to meteorology, and so far there is only one modeling study conducted by NOAA that simulates online coupling meteorology-chemistry using WRF-Chem (2-way feedback). Our preliminary tests using similar model inputs of the NOAA's study but with WRF-CAMx in standard offline coupling mode failed to re-produce the elevated ozone concentrations as simulated in the NOAA's study. In this study, we will conduct photochemical simulations using WRF-Chem with similar model configurations (e.g., same emission inventory, chemical mechanism) of WRF-CAMx, and compare ozone performance of the two model setups. Our hypothesis is the meteorology-chemistry coupling in WRF-Chem, although being more costly in computational resource, outperforms the WRF-CAMx decoupling mode. Outcomes of this study serves as basis for future cost-benefit analysis for selecting best model platform for accurate simulation of high winter ozone episodes in the Uintah Basin.