Looking at the NOAA HMS Smoke and Fire Product (top left), the small red dots indicate groups of fires, particularly the agricultural burns in Saskatchewan and Manitoba. Dust blowing over from Asia has mixed with this to create an area of increased aerosols in eastern Montana and Wyoming. The MODIS Terra image (top right) shows raised AOD values near this area, although data retrieval was inhibited by cloud cover over the eastern portions of these states.
To check to see how the aerosols are potentially affecting air quality, the middle left image is a webcam photo from Grand Teton National Park at 3:30 MDT. The visual range was 222 miles, significantly larger than even the visual range for the "clear" example in the comparison photo from the same webcam (middle right). Thus, the aerosols seem to not be affecting visibility too much.
The EPA AIRNow combined AQI animation below also shows good AQIs in Wyoming and Montana, so air quality seems to have stayed pretty fair even with the aerosols in the area. The East, however, has seen moderate and even small areas of USG AQIs today, with other elevated AQIs seen in Texas and Southern California. The current high AQI is in Nipomo, CA (119), although Susquehanna Valley is a close second (112).