False Alarm on Code Orange Ozone Alert for Charlotte and Triangle areas

The ozone alert predicted for Thursday, September 3 did not reach Code Orange levels as predicted by the Division of Air Quality in the N.C. Department of Environment and Natural Resources.

Ozone levels in the Charlotte and Triangle metropolitan areas were predicted to reach a level that can be unhealthy for sensitive groups such as children and older adults, people who work or exercise outdoors, people with heart conditions, and those who have asthma, bronchitis, emphysema and other respiratory ailments. Eight-hour ozone levels on Thursday registered well below the threshold for a Code Orange.

The reason? Air quality forecasts, like rain predictions, sometimes differ from actual conditions, primarily due to changing weather conditions. Looked at in more detail, the forecast predicted an Air Quality Index (or AQI) of 101, or just barely Code Orange, which applies when the index ranges from 101 to 150. The weather on Thursday was cloudier than expected in the Triangle, and overnight thunderstorms helped cleanse the air of pollutants. In the Charlotte area, wind likely led to lower measured levels of ozone.

How do we determine air quality forecasts?

DAQ meteorologists issue the air quality forecasts around 3 p.m. daily based on current readings from air quality monitors around the state and predicted weather patterns for the following day. A forecast that calls for elevated ozone levels, such as Codes Orange or Red, would be likely when air monitors are showing high concentrations on a given day and the weather forecast is calling for hot, sunny, calm and dry conditions the following day.

On Wednesday afternoon, when DAQ issued its Code Orange forecast for Thursday, ozone levels were approaching the Code Orange range in both the Triangle and Charlotte areas. The weather forecast for Thursday predicted sunny skies, light winds and temperatures in the mid-90s – ideal conditions for ozone formation. However, thunderstorms rolled through the Triangle on Wednesday night, and cloudiness persisted in the area during much of Thursday. Changing weather patterns in both metropolitan areas resulted in concentrations below Code Orange levels.

North Carolina’s air quality accomplishments

North Carolinians are breathing cleaner air today than at any time since the Clean Air Act was enacted in 1970. The state has reduced itstoxic air pollutant emissions by more than 80 percent during the past 15 years, and has reduced carbon dioxide emissions by more than 20 percent since 2005. For the first time in almost two decades – despite stricter standards and a growing population – the entire state meetsall federal air-quality standards. In July 2015, the Environmental Protection Agency officially recognized that all areas of North Carolina are in compliance with the 2008 federal air quality standard for ozone, a milestone capping years of improvements in air quality.Ozone levels have exceeded the standard on only two days so far in 2015, zero days in 2014 and one day in 2013. The number of high ozone days has averaged 14 days per year during the past five years and 28 days per year during the past decade. The highest number of days exceeding the ozone level was 111 days in 1999.

Protecting public health

DAQ tends to err on the side of caution when issuing air forecasts. If air quality models are predicting ozone levels that straddle the Yellow-Orange line, DAQ tends to go with the more conservative forecast, or Code Orange, because the main purpose of our air quality forecasts is to help people protect their health. DENR will continue to post daily air quality forecasts on the DAQ website at https://xapps.ncdenr.org/aq/ForecastCenter . Staff members in the DAQ encourage sensitive groups to check the air quality forecast daily.

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