Continuous, Near-Real-Time Application and Evaluation of WRF-CMAQ

As the Environmental Protection Agency's flagship air pollution modeling system, the Community Multi-scale Air Quality (CMAQ) model is being required to address increasingly complex issues related to the representation of multiple pollutants species across multiple spatiotemporal scales as well as those related to the design and implementation of more stringent NAAQS designed to protect human health and the environment. Historically, EPA scientist have evaluated retrospective, often annual length, simulations CMAQ, summarizing the performance using monthly or seasonal statistical summaries. Although informative, such an approach often masks finer scale temporal and spatial variability that greatly impacts the simulation of the atmosphere and hence air quality. To maintain CMAQ’s state-of-the-science status, as well as its ability to address emerging Agency needs, it is crucial that innovative evaluation approaches are developed and utilized that will allow for more rapid testing and hence more efficient evolution of the modeling system’s science. Accordingly, scientist at EPA began CMAQ continuously and in near real-time (CMAQ-NRT) in 2015, following the: protocol established when EPA was directly involved with NOAA’s National Air Forecast Capability (NAQFC) and recommendations published in the Bulletin of the American Meteorological Society entitled: “The Emergence of Weather-Related Test Beds Linking Research and Forecasting Operations” . CMAQ-NRT provides continuous and in near real-time evaluation at finer spatial and temporal scales which has allowed for immediate and ongoing analysis, thereby facilitating model evaluation (both performance and diagnostic) of PM_2.5 (mass only) and O₃ concentration. Observations obtained from EPA’s Air Quality System (AQS) are used in the evaluation incorporating roughly 450 PM_2.5 mass and 900 O₃ monitors. Results are provided using a variety of statistical and visualization tools and have led improvements across pollutants (PM_2.5 and O₃ concentrations), years (2015-2019) and meteorological, chemical and emissions processes. Additionally, output from CMAQ-NRT is being archived and has been made available for dissemination to scientists across EPA and external agencies.