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What is the AQI?
The AQI is an index for reporting daily ground level air quality. It tells you how clean or polluted your air is, and what associated health concerns you should be aware of. The AQI focuses on health effects that can happen within a few hours or days after breathing polluted air. EPA uses the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established national air quality standards to protect against harmful health effects. The State of North Carolina uses the same definitions and terms as EPA, except for special cases. For example, the NC Air Awareness program uses "ozone AQI" values the during the summer ozone forecasting season. In winter months, the AQI (maximum among pollutants) could be due to PM2.5, ozone or carbon monoxide for a particular area. High ozone levels are the primary cause of higher AQI values in summer months. AQI ranges and health notices are: 0 to 50 = Good Air Quality; 51 to 100 = Moderate; 101 to 150 Unhealthy for Sensitive Groups; 151 to 200 = Unhealthy; 201-300 = Very Unhealthy.
Are these REAL-TIME readings?
No, but by definition the AQI is taken from a set of hourly readings. The smallest increment of readings from continuous gas instruments is one-minute averaged values, however, these readings are hourly averaged values acquired several times per day. Ozone and continuous PM2.5 measurements are aggregated into one hour averaged values and then the polling from the site occurs several times per day, but NOT hourly.
What do you mean by "latest AQI readings"?
"Latest AQI readings" refers to those AQI values taken from the stream of hourly values for the set of pollutants monitored. Ozone AQI is taken from a set of the latest correctly computed hourly values (last 24 hrs of valid eight-hour averages). Note the highest of those most recent 24 values could be from ozone observations of 25-30 hours before the current clock time.
Where do I get more air quality data?
For NC data collected by DAQ, send your requests to Ask_DAQ_Ambient.
For access to Forsyth County air quality data, click here.
For access to Mecklenburg County air quality data, click here.
In addition to DAQ, one may obtain data from the US EPA web page. The EPA web page for accessible NAAQS data by the web is located at: http://www.epa.gov/air/data/index.html.
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Why display the AQI on a WEB page?
The internet provides another way in addition to news media for North Carolina to publicize the AQI. The newspapers can check the AQI values without relying on emails or calls to or from the North Carolina Division of Air Quality (DAQ). The federal register requires state agencies to display or advertise the AQI for metropolitan areas. Posting real-time data is not part of the requirement.
What do you mean by "time recorded"?
"Time recorded" refers to the hour the pollutant responsible was reported as a maximum. The hours start at midnight (00), and are reported as 12 AM if the value for that pollutant reached its maximum between 00:00 and 00:59 min:hrs. Since the AQI is the maximum chosen among all reported averages for the past 24 hours, a time recorded could be more than 24 hours before the time one is viewing the web page. For example, assuming one is viewing the web page at 6pm today and ozone is the responsible pollutant, the ozone readings for the AQI could involve values from yesterday between around noon to present.
Why are the AQI values shown today from yesterday's data?
The AQI values computed for each pollutant are calculated differently. The DAQ's "standard" AQI report is defined as the maximum among all AQI values that can be calculated during the 24 hours prior to the time the report is created. Sometimes this will indeed be an AQI that occurred on the previous day.
Can I look up the AQI from this date last year? Last month?
Send an email to Ask_DAQ_Ambient to inquire or obtain AQI data from the Data Management and Statistical Services Branch, Division of Air Quality, Raleigh, NC
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