How are Air Quality Forecasts made and how do they help?

Over the past decade, more state and local agencies have begun air quality forecasting for their communities. Today, about 300 cities nationwide are issuing air quality alerts based on forecast concentrations of known pollutants such as ozone and particle pollution; but without the benefit of the kind of high-powered national forecasting technology and guidance that supports local weather forecasts. For localities that have been forecasting air quality, new NOAA forecasting guidance is improving forecasters’ ability to predict the onset, severity, and duration of poor air quality. For communities in most of the country, this will be the first time that comprehensive air quality predictions, with hour-by-hour information for cities, suburbs and rural communities alike will be available.

NOAA, in partnership with EPA, has implemented the first stages of an air quality forecast (AQF) capability. Now providing ozone forecast guidance for the eastern U.S. (predictions available at, the AQF capability uses the National Weather Service’s most advanced operational computer weather models at NOAA’s National Centers for Environmental Prediction (NCEP) coupled with a community multi-scale air quality (CMAQ) chemical transport model to produce daily forecast guidance for surface ozone. Meteorological information such as current and predicted temperature, humidity, winds, cloudiness, and precipitation, combined with pollutant emissions data supplied by EPA, are input to CMAQ to predict ozone concentrations through the next day. In summer, 2006 an experimental version of the AQF capability will cover the lower 48 states. Currently, the AQF capability covers the eastern US from the Atlantic Seaboard to the Mississippi Valley, with hourly and 8-hourly forecast ozone concentrations out to midnight, next day, at 12 km (about 7 miles) grid resolution. This information, converted to EPA’s health-based Air Quality Index (AQI) is also available on EPA’s AIRNow website.

Sample Air Quality Forecast Guidance - click to enlarge

Conus Mid-Atlantic Georgia

The Air Quality Index (AQI): The AQI is a color-coded index describing how clean or polluted the outdoor air is in a specific location and what associated health effects may result for the local population. The AQI focuses on health effects a person may experience within a few hours or days after breathing polluted air. EPA has established AQI scales for five major pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these, EPA has established national air quality standards to protect public health. State and local air quality agencies participating in the AIRNow program, post air quality conditions and their forecasts/alerts in terms of the AQI on EPA’s AIRNow site:

In the next few years, the operational ozone prediction domain will be expanded still further to include Alaska and Hawaii and the forecast range will be extended out to several days. Also in development are predictions of airborne particulate matter (PM). As a component of the eventual PM forecast capability, a daily smoke forecast tool is being tested experimentally. For this tool, NOAA’s National Environmental Satellite and Data Information Service provides fire locations of active fires from complex satellite-based imaging techniques. Smoke transported from these fires is simulated with a computer transport model called HYSPLIT linked to NWS’ operational weather forecast models. Predictions of the smoke are updated each morning and provided on a web site at State and local air quality forecasters will be able to use the expanding guidance when they prepare their forecasts or issue local alerts for their communities. The public, especially those with greater sensitivity to poor air quality, will be able to see hour-by-hour trends for the entire Nation and take appropriate actions.


What are state air quality forecasters saying?
“The NOAA forecast model is one of several important tools that we evaluate daily prior to making and issuing our air quality forecasts for Virginia during the ozone season. We have found it to be quite valuable when used in concert with our other forecast methods. It provides model forecasts for ozone concentrations at specific locations based upon a meteorological model and air chemistry conditions. Prior to the availability of the NOAA forecast model, our forecasts were based solely on statistical relationships between various meteorological parameters and current air quality conditions. The NOAA forecast model has provided us with another method to produce our forecasts. We look forward to the NOAA forecast model inclusion of particulate concentration forecasts in the future which will provide an additional tool for our air quality forecasts.”
              -Dan Salkovitz, meteorologist
              Virginia Department of Environmental Quality

“ The NOAA ozone model provides us with an additional tool that enables us to better inform the general public of potential air pollution concerns. DES is pleased to participate in the application of the NOAA model for regional ozone forecasting, and look forward to the planned improvements that will increase the resolution of the ozone model and the development of a small particle model. New Hampshire is committed to using the best available tools for air pollution forecasting and looks forward to continuing our working relationship with NOAA, EPA and the National Weather Service in the area of air pollution forecasting.”

              -Lisa L. Landry, air dispersion modeler
              New Hampshire Department of Environmental Services