Understanding the Air Quality Index (AQI)

An air quality index (AQI) value is assigned through the measurement of 5 variables (criteria pollutants): surface ozone, particulate matter (particle pollution), carbon monoxide, sulfur dioxide, and nitrogen dioxide.  Each of these variables is assessed relative to standards (0-500; 0-100 being the set AQI to meet air quality standards that meet satisfactory human health) set by the EPA based upon ambient air quality related to affected groups of people. Six divisions of the AQI were created to help the general public visualize and understand their localities ambient air quality in relation to individual health. This is done through the use of colors and values as shown below. If you would like to know todays and tomorrow's Air Quality for Medina, Portage, and Summit Counties click here. If interested in detailed maps of northeast Ohio's air quality select NOACA. If interested in the air quality across the United States, refer to AIRNow. Both NOACA and AIRNow provide extended forecasts.

How is our Air Monitored?

The criteria pollutants (ozone, particulate matter, carbon monoxide, and sulfur dioxide) are monitored through the use of multiple monitors specifically designed to the specified criteria pollutants being analyzed. These monitors collect samples to ensure that air quality standards are being met or trying to be obtained and so general concentrations of criteria pollutants are continuously being monitored. There are three types of monitors, continuous, intermittent, and speciation:

• Continuous monitors collect data everyday for a 24 hr. period and is downloaded at 8 A.M. and 4 P.M. to an EPA server. The criteria pollutants continuosly analyzed are ozone, PM_2.5, carbon monoxide, and sulfur dioxide.

• Intermittent monitors are only run one of three days for a 24 hour period from 12 midnight to 12 midnight. From a filter, particulate matter (PM_2.5 and PM₁₀) is manually collected,  weighed, and sent for further analysis. A similar process is used for analyzing lead.

• Speciation monitors are only run one of six days for a 24 hour period from 12 midnight to 12 midnight. Data is manually accessed at these monitors and then sent for further analysis. This monitor uses filters to collect major components of particulate matter less than 2.5 micrometers (PM_2.5). These major components are sulfate, nitrate, organics, elemental carbon, and soil (NaCl is another major component if a coastal site).