N.C. Department of Environment and Natural Resources
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Monitoring & Emissions Data >> Latest Available Air Quality Index Readings

General Information about AQI
What is one-hour ozone?
How does the eight-hour ozone AQI differ from the forecast ozone AQI?
For which Metropolitan Statistical Areas of NC is the AQI required to be published?
Is the State of NC responsible for Charlotte and Winston-Salem AQI system? What is a local program?
What about carbon monoxide and cars?
How does do these AQI values differ from forecast AQI values?
How do near real time readings differ from the web displayed AQI values?
      What is eight-hour ozone?
What is a Metropolitan Statistical Area (MSA)?
What is a "critical pollutant"?
Where do I get the AQI for Jacksonville (Roanoke Rapids, Eden, Mount Pilot, Kure Beach, etc.)?
How often does this page update?
How do I know what hour the highest value occurred?
Can I look up the AQI from this date last year? Or one from last month or last week?

What is one-hour ozone?
DAQ records ozone concentrations reported in intervals of 1-hour averages, 24-hours per day at each monitor. The ozone is measured in units of parts per million, or converted to parts per billion ozone.

How does the eight-hour ozone AQI differ from the forecast ozone AQI?
DAQ forecasts an "ozone Air Quality Index value". It does not forecast the AQI per se. Most violations of air standards in the summer ozone season are from ozone peak values, rather than other pollutants.

For which Metropolitan Statistical Areas of NC is the AQI required to be published?
AQI reporting is mandatory for MSAs with populations greater than 350,000 in the most recent 10-year census. In NC, these areas include: Charlotte-Gastonia-Rock Hill (1,499,000), Greensboro-Winston-Salem-High Point (1,252,000) and Raleigh-Durham-Chapel Hill (1,188,000).

Is the State of NC responsible for Charlotte and Winston-Salem AQI system? What is a local program?
The Mecklenburg County and Forsyth County governments operate autonomous monitoring networks separate from the state. Each agency has a different arrangement for sharing its data with the DAQ.

What about carbon monoxide and cars?
DAQ monitors for carbon monoxide specific areas of NC, but the concentrations have decreased by more than 75% in the last 20 years. The carbon monoxide levels are higher in the winter season CO levels are reported as running eight-hour averages of hourly recordings.

How does do these AQI values differ from forecast AQI values?
The AQI is a reported set of observed values, whereas the forecast AQI is a predicted index value for a region. All AQI data are permanently stored at the end of the summer ozone season.

How do near real time readings differ from the web displayed AQI values?
After real-time ambient data has been polled and screened, the data are stored in NC and the EPA Air Quality System database. Archived data will be "quality assured" to a greater extent, which could result in slightly different data values from the web displayed AQI site values. We also may calculate historical AQI results obtained from different instruments than those used for the daily AQI reports. These different instruments using different measurement technology may in fact report slightly different concentrations and AQI numbers for identical samples of air.

     

What is eight-hour ozone?
The eight-hour ozone value is the average of 8 contiguous hours recorded. The maximum of all such values that day is the eight-hour ozone daily max.

What is a Metropolitan Statistical Area (MSA)?
DAQ is obligated to report the AQI for all ambient air pollutant data monitored under the requirements of the Clean Air Act Amendment of 1990. The MSA is defined by the US Department of Commerce, Bureau of The Census. MSA is a geographic entity designated as one or more counties in a metropolitan area, except in New England, where MSA is defined in terms of county subdivisions.

What is a "critical pollutant"?
A "critical pollutant" is the pollutant with the highest recorded Air Quality Index (AQI) number among all monitors in the area during a given time period.

Where do I get the AQI for Jacksonville (Roanoke Rapids, Eden, Mount Pilot, Kure Beach, etc.)?
AQI reports are required for Metropolitan Areas of a certain size, and none of these areas are that large. However, upon special request, the DAQ can provide appropriate information about those areas in which we operate the same kind of monitors.

How often does this page update?
The AQI page is refreshed with new data on a fixed schedule throughout the day at about: 5:00 am, 7:45 am, 11:45 am, 3:45 pm, 7:45 pm, 11:15 pm. Additional updates during the summer ozone season occur at 2:45pm and 6:45pm.

How do I know what hour the highest value occurred?
AQI calculations are based on pollutant concentrations averaged over 8 hours (CO and ozone) or 24 hours (PM), so the highest single hour is not readily available; either the beginning hour or the ending hour of the highest-average time interval is reported, depending on conventions established by the EPA.

Can I look up the AQI from this date last year? Or one from last month or last week?
The AQI data reported daily are provisional estimates of recent air quality. However, the values could change as result of data QC procedures. Approximately 2 months after any given date, NC DAQ can provide a "historical" value of the AQI from our data archives.


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Last Modified: Mon October 06 08:05:09 2008

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