In its fifteenth annual "State of the Air" report, the American Lung Association gave Missoula an "F" for 24-hour particle pollution levels.

"Missoula actually ranked among, unfortunately, our most polluted [counties] for something we call short term particle pollution. What that means is that there were too many days when high levels of fine particles spiked to levels that were unhealthy and could be unhealthy for people to breathe, causing a whole host of problems.

The study looked at air quality between 2010 and 2012. Nolen says small particles in the air are particularly harmful.

"Particles are little bits of things, often they are ash or soot, but even finer than that, they are things that are roughly one-thirtieth of a human hair, and they can pass through the bodies defense mechanisms and lodge deep in the lungs and can cause real problems to your health."

On a postivie note, Missoula received an "A" grade in the same report for having low levels of ozone in the air. Curiously, although the 24 hour study on particle pollution gave Missoula a failing grade, Missoula received an "A" for particle pollution when looked at on an annual