Undated (KELO AM) - The haze you see this Monday night is the smoke from the Canadian wildfires.
Unprecedented coverage of fires from Alaska into a large portion of western Canada are creating periods of hazy skies and reduced visibility in the northern United States as the smoke becomes trapped in a prevailing northwesterly flow of air. During periods when the smoke filters to the surface, it will create reduced air quality, which can affect persons with respiratory issues and other sensitivities to small particulate matter.
Earlier this evening the Air Quality Index in Sioux Falls was in the unhealthy category.
Here are a few resources from http://www.airnow.gov which may help you decide whether it is safe for you to spend prolonged time outdoors.