Treasure Valley air quality has improved so much that the Boise metro area (including Nampa) has been listed among the Top 25 cleanest cities for annual particle pollution in the United Sates.
The American Lung Association's State of the Air 2012 moved Ada County smog levels from an "F" ranking in its last report up to a "C" grade. Ozone (smog) is the most widespread air pollutant, created by the reaction of sunlight on emissions from vehicles and other sources. Ozone is blamed for wheezing, coughing, asthma attacks and premature death.
On the downside, Benewah, Lemhi and Shoshone counties all received an "F" in the latest report for short-term particle pollution.
The air is a bit clearer in Butte and Kootenai counties—two of the cleanest, when it comes to ozone.
But the Lung Association still warned that more than 40 percent of people in the United States—more than 127 million people—live in areas where air pollution continues to threaten their health.