A numerical daily air quality forecast system for the Pacific Northwest

A real-time photochemical air quality forecast system has been implemented for the Puget Sound region to support public awareness of air quality issues. The Air Indicator Report for Public Access and Community Tracking (AIRPACT) forecast system uses daily numerical weather forecasts from the fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) to drive the California Meteorological Model (CALMET)/California photochemistry grid model (CALGRID) Eulerian photochemical modeling suite. Hourly forecasts of ozone and other pollutant concentrations, including primary particulate emissions from diesel sources, are produced for urban Seattle and environs within a gridded domain consisting of 62 x 67 grid cells (4 km x 4 km) with 13 vertical layers. Detailed gridded emission inventories are adjusted dynamically for time of day, day of the week, month, and gridded ambient temperatures to generate requisite emissions. The forecast system also uses hourly pollutant observation data, reported daily, to perform automated evaluations of forecast accuracy. Forecasts and verification results are provided on a daily basis via the Web (see www.airpact.wsu.edu). This paper describes the forecast system and presents preliminary forecast evaluation results from the Pacific Northwest 2001 (PNW2001) field program and from selected months using the routine monitoring network. AIRPACT is unique nationally as the sole numerical modeling system producing daily, year-round, high-resolution regional air quality forecasts with daily verification.