Data coverage
The National Air Quality Forecasting Capability (NAQFC) dataset contains model-generated air quality (AQ) forecast guidance from three different prediction systems. The first system is a coupled weather and atmospheric chemistry numerical forecast model, known as the Air Quality Model (AQM). It is used to produce forecast guidance for ozone (O3) and particulate matter that is less than or equal to 2.5 micrometers in diameter (PM2.5). Prior to May 14, 2024, AQM predictions were derived using the EPA’s Community Multiscale Air Quality (CMAQ) model, driven by meteorological fields from NCEP’s operational weather forecast models, specifically the North American Mesoscale Model (NAM; prior to 20 July 2021) and the Global Forecast System (GFS; beginning 20 July 2021). Since May 14, 2024, AQM guidance has been produced by a unique application within the community-based Unified Forecast System (UFS). The core model components in this application are derived directly from the fully online-coupled UFS-based weather and CMAQ-based chemistry models. In addition, it incorporates information related to chemical and particle source emissions as it integrates forward in time, including anthropogenic chemical emissions provided by the EPA, fire emissions from NOAA/NESDIS, and airborne particles generated by human activities and those predicted to be generated by wind-driven erosion and biosphere at ground level. The NCEP NAQFC AQM output fields in this archive include model raw and bias-corrected predictions dating back to 1 January 2020, all generated by the contemporaneous operational AQM, beginning with AQMv5 in 2020, transitioning to AQMv6 on 20 July 2021, and to AQMv7 on 14 May 2024. The length of each forecast was 48 hours prior to the implementation of AQMv6, and has been 72 hours ever since. The history of AQM upgrades is documented here The second prediction is known as the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT). It is a widely used atmospheric transport and dispersion model containing an internal dust-generation module. It provides forecast guidance for atmospheric dust concentration and, prior to 28 June 2022, it also provided the NAQFC forecast guidance for smoke. Starting on that date, the third prediction system, a regional numerical weather prediction (NWP) model known as the Rapid Refresh (RAP) model, subsumed HYSPLIT for operational smoke guidance, simulating the emission, transport, and deposition of smoke particles that originate from biomass burning (fires) and anthropogenic sources. The output from each of these modeling systems is generated over three separate domains, one covering CONUS, another over Alaska, and the other over Hawaii. Currently, for this archive, the O3, PM2.5, and smoke output is available over all three domains, while dust products are available only over the CONUS domain. The predicted concentrations of all species in the lowest model layer (i.e., the layer in contact with the surface) are available, as are vertically integrated values of smoke and dust. The data is gridded horizontally within each domain, with a grid spacing of approximately 5 km over CONUS, 6 km over Alaska, and 2.5 km over Hawaii. O3 concentrations are provided in parts per billion (PPB), while the concentrations of all other species are quantified in units of micrograms per cubic meter (ug/m3), except for the column-integrated smoke values which are expressed in units of milligrams per square meter (mg/m2). Temporally, O3 and PM2.5 are available as maximum and/or averaged values over various time periods, selected in part for consistency with the EPA’s National Ambient Air Quality Standards. Specifically, O3 is available in both 1-hour and 8-hour (backward calculated) averages, as well as preceding 1-hour and 8-hour maximum values. Similarly, PM2.5 is available in 1-hour and 24-hour average values and 24-hour maximum values. In addition, all O3 and PM2.5 fields are available with bias-corrected magnitudes, based on derived historical model biases relative to observations. The AQM produces hourly forecast guidance for O3 and PM2.5 up to 72 hours twice per day. Smoke guidance is available up to 51 hours from once-per-day RAP forecasts, while dust guidance from HYSPLIT is available up to 48 hours.
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