US National Air Quality Forecast Capability: Expanding Coverage to Include Particulate Matter

Abstract

The US National Air Quality Forecast Capability (NAQFC), developed by the National Oceanic and Atmospheric Administration (NOAA) in partnership with the Environmental Protection Agency (EPA), currently provides next-day operational predictions for ground level ozone and smoke for 50 US states. Ozone predictions are produced with the Community Multiscale Air Quality (CMAQ) model driven by NOAA's operational North American Mesoscale weather forecast Model (NAM); routine verification is conducted with monitoring data compiled by the EPA. Smoke prediction relies on satellite detections of smoke sources, US Forest Service emission estimates, with transport and dispersion simulated by the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model driven by NAM; routine verification is conducted with satellite observations of smoke. Quantitative predictions of fine particulate matter (PM2.5) are in development. Inventory based simulations using CMAQ with aerosol modules show seasonal biases: overestimating in wintertime and underestimating in summertime. Current testing focuses on including intermittent aerosol sources directly emitted by wildfires and dust storms within the forecast domain; longer-range transport of dust is incorporated through lateral boundary conditions. For example, simulations of trans-Atlantic transport of Saharan dust, injected into the prediction domain, contribute enhanced surface PM2.5 concentrations in the southern US, as observed in surface monitoring. Simulated PM2.5 concentrations are being evaluated with speciated observations in order to improve seasonal biases in predictions. Research on assimilating PM2.5 surface observations shows potential to improve predictions. Furthermore, analysis of discrepancies between observations and model predictions that are produced during assimilation can provide insight on impacts of proposed improvements to PM2.5 predictions.