AQI imagery from EPA AIRNow shows areas of Moderate air quality in the southeast, southern plains, Pacific southwest, and around the Great Lakes. One area of Unhealthy showing up on the AQI loop in northern Texas. Unfortunately the area is under some spotty clouds, seen below right in MODIS AQUA imagery, so satellite data won't be much help identifying the cause.
The latest NAAPS run, shown below left, indicates dust as a likely cause, supported by reports of blowing dust and high winds from local meteorological reporting stations. Tomorrow's forecast, shown below right, shows winds in the area again, but not quite as high as today's.
The NWS dust forecast for tomorrow, below left, as well as the NAAPS run above, show that the low sitting over the Great Lakes and the areas of high pressure behind it, seen in the NWS surface analysis below right, will move the dust off to the south, before stirring up another batch of dust north of the area and blowing that south.