The DNR uses weather forecasts and data from air monitoring sites to determine air quality in the state, and notifies residents when pollutants reach unhealthy levels based on the Air Quality Index (AQI) [exit DNR]. The AQI corresponds to the national ambient air quality standard for several air pollutants regulated by the Clean Air Act. To protect public health, as resources allow, DNR may issue an air quality advisory for a county when the AQI exceeds, or is expected to exceed, the level of the ozone or fine particle (PM2.5) standard.
The ozone AQI is calculated from 8-hour rolling average concentrations. The PM2.5 AQI is calculated using the 24-hour rolling average concentrations from the continuous monitors.
| AQI Levels of Health Concern |
Numerical Value | 8-hr Ozone (ppb) | 24-hr PM2.5 (ug/m3) |
|---|---|---|---|
| Good | 0-50 | 0-54 | 0.0 to 12.0 |
| Moderate | 51-100 | 55-70 | 12.1 to 35.4 |
| Unhealthy for Sensitive Groups | 101-150 | 71-85 | 35.5 to 55.4 |
| Unhealthy | 151-200 | 86-105 | 55.5 to 140.4 |
| Very Unhealthy | 201-300 | 106-200 | 140.5 to 210.4 |
| Hazardous | > 300 | > 201 | > 210.4 |
The U.S. Environmental Protection Agency (EPA) establishes the national air quality standards at levels that protect human health, and reviews and updates the standards periodically based on the latest available science. In 2015, EPA strengthened the ozone standard from 75 parts per billion (ppb) to 70 ppb.
The AQI for ozone was adjusted in 2016 to reflect the updated ozone standard. In general, the level of the standard corresponds to an AQI value of 100. Values up to 100 are typically considered protective of human health. Under the new 2015 ozone standard, an AQI value of 100 corresponds to an ozone concentration of 70 ppb. Under the previous standard, an AQI value of 100 corresponded to a concentration of 75 ppb.
Air quality advisories are issued when the AQI reaches, or is expected to reach, a value of 100. Because the ozone standard has been lowered to 70 ppb, the department may issue air quality advisories more often and for a greater number of counties than in previous years, even if the air quality itself has not changed.
For this reason, a more frequent issuance of air quality advisories does not necessarily mean the air quality in any particular county is worse than before. In fact, air quality has been improving across the state. For more information, visit Wisconsin's air quality trends. For more information about the 2015 ozone standard, visit Ozone.
| AQI Levels of Health Concern |
Numerical Value | 8-hr Ozone Concentration (ppb) | |
|---|---|---|---|
| 2008 Ozone Standard | 2015 Ozone Standard | ||
| Good | 0-50 | 0-59 | 0-54 |
| Moderate | 51-100 | 60-75 | 55-70 |
| Unhealthy for Sensitive Groups | 101-150 | 76-95 | 71-85 |
| Unhealthy | 151-200 | 96-115 | 86-105 |
| Very Unhealthy | 201-300 | 116-374 | 106-200 |
| Hazardous | > 300 | > 375 | > 201 |