In 1997, the North Carolina Division of Air Quality (DAQ) began issuing ozone forecasts during the summer ozone season. Initially designed for the Federal 1-hour National Ambient Air Quality Standard (NAAQS) and produced for a single location, the forecasting program changed in 1998 to accommodate the 8-hour NAAQS for ozone and expanded each subsequent year with forecasts now issued for five metropolitan areas.

While air quality forecasting is similar to routine weather forecasting, the air quality forecasters’ requirements for atmospheric data extend beyond those of their National Weather Service Forecast Office (NWSFO) counterparts. Monitoring and analyzing atmospheric chemical constituents in real time as well as assessing detailed characteristics of the planetary boundary layer (PBL) are the first steps in producing the background diagnoses from which the next day’s air quality forecasts are made.

AQ forecasters in North Carolina exploit a robust network of ~50 ozone monitors operated by DAQ and other AQ agencies in NC. With one monitor per 1000 square miles, this is one of the densest statewide ozone monitoring networks in the nation. In addition to these surface monitors, DAQ operates three ozone monitors above the surface on a 600-meter TV tower, a unique data source invaluable to ozone forecasting.

These data are integrated into fine-scale analyses that include standard surface reports from Federal Aviation Administration (FAA) and NC Department of Transportation (DOT) ASOS & AWOS sites augmented with reports from North Carolina State University’s (NCSU) Agricultural Weather Network (AgNet). The AgNet, operated by the State Climate Office of North Carolina, includes 25 statewide sites with standard temperature, dewpoint, pressure, winds, and rainfall; but AgNet adds solar radiation, soil moisture and soil temperature and, at some sites, an additional 10-m temperature, critical for determining surface fluxes important to the planetary boundary layer ­ and thus pollutant ­behavior.

Because the AQ forecasting requirements for a seven-county area in the mountains of western NC specify both valley and ridge-top (below and above 4,000 ft MSL, respectively) forecasts, DAQ installed three high-elevation meteorological sites in this otherwise data-sparse area to supplement the few airport sites in the mountain valleys. To better resolve the terrain effects on both weather and pollutant behavior, forecasters also tap National Park Service and US Forest Service AQ and meteorological sites in the Great Smoky Mountains, including a “web cam” site reporting nephelometer-derived visual range.

In addition, AQ agencies operate seven other meteorological sites in the state, each collocated with both ozone and continuous fine particulate monitors.

DAQ also owns and operates two 915 MHz boundary layer profilers with radio acoustic sounding systems (RASS), one at Charlotte/Douglas International Airport (KCLT) and one near Raleigh. The Raleigh profiler site is about 8 km from the TV-tower mounted ozone monitors and is collocated with one of the surface ozone monitoring sites.

These data have allowed AQ forecasters in North Carolina to developcredible ozone and fine particulate forecasting capabilities.