A Framework to Improve Chemical Lateral Boundary Conditions in Support of NOAA’s Air Quality Forecast Capabilities

Air quality forecast models such as the National Air Quality Forecast Capability (NAQFC) operated at NOAA can suffer deficiencies in chemical lateral boundary conditions (CLBCs) representations by using climatologically averaged conditions, which may limit its forecast accuracy in both ozone and PM_2.5. This problem can be more prominent during extreme chemical weather episodes, such as wildfires and dust storms. Since the use of real-time CLBCs from global chemical transport models is not available in the near future, we develop an alternative solution that utilizes both more up-to-date climatological CLBCs and event-based CLBCs to improve NAQFC’s forecast skills. As such, we are constructing a database of CLBCs under various trans-boundary transport scenarios using the NASA GEOS-5 global circulation transport model. A trigger mechanism has been developed to determine when and where to implement which CLBCs based on surface air quality monitoring and satellite AOD observations. This alternative CLBCs framework has been tested for the months of 2015 when Saharan dust intrusion and Canadian wild fire plume transport occurred. The results show that the application of the event-based CLBCs improves NAQFC’s performance in reproducing the temporal and spatial variations of the episodes. The advantage of such a framework also includes that the CLBCs database can easily been expanded when more chemical transport events are observed and simulated, and that the trigger mechanism can be refined when more observational data and analysis are available.