The Air Quality Index reflects air pollutants of the greatest concern in Minnesota: ozone, which causes respiratory problems, and fine particles, which cause respiratory and cardiovascular problems. When this index reaches a certain threshold, an air quality alert day is called. Air quality alert days may be called in one or more of the nine regions distributed across the state. The number of days in Minnesota with Air Quality Alerts is an indicator of the quality and cleanliness of the air in Minnesota. While on the majority of days the air is healthy to breathe, there may be a few days each year when air quality becomes unhealthy. Fewer of these air quality alert days is better. Many factors contribute to poor air quality, including local air pollution emissions, weather, wildfires, and emissions from sources outside of Minnesota's boundaries.
In 2017 there were zero air quality alert days, which is a good result by historic standards and represents an improvement from five air quality alert days in 2015. Weather conditions can greatly affect the number of air quality alert days from year to year and Minnesota Pollution Control Agency staff attributes some fluctuations in recent years to such factors.
This document (.xlsx) provides the indicator data in table format.