Wildfire smoke from Canada, and the smoke from fires within Montana dropped the Air Quality Index (AQI) in parts of Montana by dozens of points on Wednesday. Thursday isn't looking too promising either with Air Quality Alerts and Heat Advisories in effect for large portions of the state.
Yellowstone National Park, along with most counties in western Wyoming are still dealing with unhealthy air quality. The air quality index for YNP has been hovering around 100 which is "unhealthy for sensitive groups".
A couple of air quality monitoring stations around Billings had readings in the "unhealthy" range on Monday (7/26), and with a high concentration of pollutants expected to continue from western wildfires, being outdoors will make it hazardous for some groups this week.