2 Ground Level Ozone Concentrations in North Carolina Ambient levels of ozone vary by region, time of day, the presence of ozone-forming compounds, and weather conditions. Estimated summer daytime levels in the United States average 0.025-0.045 ppm over 8 hours. This is due to mountain breezes blowing steadily upslope by day and downslope at night, and sea breezes blowing steadily inland by day and out to the sea at night. 6 Ozone levels tend to be highest in urban areas such as Charlotte, Raleigh, Durham, Greensboro, Winston-Salem, and Fayetteville, and in the Great Smoky Mountains. These levels are high enough to cause adverse health effects even in healthy individuals.
Most ozone monitoring data focus largely on outdoor ozone concentrations.
However, there is some information on indoor concentrations. Ozone-generating air cleaners can produce significant ozone concentrations, but most indoor ozone comes from outdoors. Based on reported ratios of indoor to outdoor ozone, it seems likely that indoor ozone exposure may sometimes be significant. These findings are of particular concern to susceptible populations occupying urban buildings with no air-conditioning and high intakes of outside air. During the season, the DAQ forecasts ozone levels for each upcoming day using meteorological and non-meteorological data.