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Mecklenburg County Ozone Monitoring

Mecklenburg County Air Quality (MCAQ) operates three ozone-monitoring sites that span the county from southwest to northeast.  The sites operate continuously from April 1 through October 31.  Every ten seconds each ozone analyzer measures the ozone concentration in the ambient air. 

A computer called a data logger is connected to each analyzer.  The computer records each ten second reading.  These readings are compiled into one-minute averages and stored.  The one-minute averages are compiled into one-hour averages and stored. 

The data is downloaded to the MCAQ central computer every hour, which then updates our Air Quality Monitoring page here.

Afternoons Are Unhealthy
Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds.  Ozone formation in our area exhibits a diurnal pattern.  Ozone levels begin the day at relatively lower levels and rise as the outdoor temperature rises.  Concentrations generally peak between noon and six pm.  The maximum eight-hour ozone Air Quality Index is typically reported by the SMOGLINE between six and eight pm as the data becomes available. 

The three sites operated by MCAQ provide neighborhood and urban scales of representation.  The County Line ozone-monitoring site is classified as an urban scale of representation.  Urban scale measurements are used to estimate concentrations over large portions of an urban area.  The Garinger High School and Arrowood monitoring sites provide information from urban areas characterized by residential and commercial land use and are called neighborhood scale.  Under stagnation conditions, a station located in the neighborhood scale may experience peak concentration levels within an urban area. 

Air Quality Index
Ambient air pollutant concentrations are reported as the air quality index (AQI).  An AQI value of 100 generally corresponds to the national air quality standard for the pollutant of concern, which is the level EPA has set to protect public health.  AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy - at first for certain sensitive groups of people, then for everyone as AQI values get higher. 

The pollutant most often impacting Mecklenburg County is based on the eight-hour concentration of ozone.  Eight-hour concentrations are calculated by averaging eight consecutive one-hour values.  The reported value is a rolling average assigned to the beginning hour of the eight hour period.  For example:  an average is calculated from 8:00 am through 3:59 pm.  The value is assigned to hour 8:00 am and reported after the 4:00 pm data download.

Regional Air Quality Data
Eight ozone monitors are operated in our region, three by Mecklenburg County, four by the North Carolina Division of Air Quality (NCDAQ)  and one by the South Carolina Department of Health and Environmental Control (SCDHEC) Bureau of Air Quality  These sites send data to the national ozone mapping system, which reports data from hundreds of sites located throughout the U.S. at

Ozone forecasts for the Charlotte area are done by NCDAQ and can be found at:

 More information on ground level ozone can be found at USEPA Office of Air and Radiation at

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