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Air Quality Index

Air Quality Indiex

Mecklenburg County Air Quality is responsible for compiling and reporting the Air Quality Index (AQI) in Mecklenburg County.  The index provides information on pollutant concentrations for ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.  The AQI is calculated daily for each monitored pollutant.  The pollutant with the highest AQI value is designated as the critical pollutant for that particular day.

 Values equal to or less than 100 on the index scale are considered "good" to "moderate" air quality; values greater than 100 are considered unhealthy. Specific information regarding the health effects of the AQI pollutants are reported as required.

For the Charlotte area, during summer months, ozone is usually the critical pollutant. During the remainder of the year, particulate matter and carbon monoxide are the critical pollutants in our area.

The Revised AQI
In August 1999, the AQI reporting system was revised to incorporate two new standards as required by EPA regulations promulgated in July 1997. The previous ozone standard was 0.12 parts per million (ppm) averaged over a one hour period.  The revised ozone standard is 0.08 ppm averaged over an eight hour period. Fine particulate matter less than or equal to an aerodynamic diameter of 2.5 microns (PM 2.5), was also added to the required parameters.  To complement specific information regarding the health effects of the various pollutants, the revised AQI went a step further and identified sensitive groups for each pollutant:

  • Ozone - People and children with asthma
  •  Particulate Matter 2.5 - People with respiratory or heart disease, the elderly and children
  • Particulate Matter 10 - People with  respiratory disease
  • Carbon Monoxide - People with heart disease
  • Sulfur Dioxide - People with asthma  

Colors were assigned to each index level and correlated to specific descriptors.  The colors are used to alert the public by means of the ozone mapping system.  The ozone AQI is available on the web at from May through September in the form of a map depicting hourly concentrations using the color descriptors.

Air Quality Data and Trends
For real time information on Mecklenburg County's ambient air monitoring program click on  Current Mecklenburg County  Air Quality. You will be directed to the GIS Air Quality Monitoring website where real time air quality data from each of the Mecklenburg County air monitoring sites an be found.

The public may also dial (704) 333-SMOG (7664) to access a computerized AQI message that is updated hourly. The message provides the current AQI for Mecklenburg County.  The AQI for the preceding day is published daily in The Charlotte Observer weather section. 

Data Collection
Data collected at an air monitoring station is used to calculate the AQI 


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