Today’s Terra MODIS image (below left) is a dramatic depiction of both Tropical Depression Gustav, nearly stationary over the mid-Mississippi River Valley, and lingering haze in the Midwest. Haze can be seen to the south and southwest of Lake Erie (right side of left picture). Zooming out to a more regional view, Google Earth (below right) shows us the maximum AQI measured on the ground for whichever pollutant is dominating, either PM2.5 or ozone. Several readings in the Midwest are Code Orange (Unhealthy for Sensitive Groups) for both PM2.5 and ozone. Farther east, it is only ozone causing the Code Orange from Washington DC up to Philadelphia.
The rest of the country is relatively quiet in terms of air quality (AIRNow PM2.5 and ozone), except for some isolated fires in California, and a lingering plume of SO2 from the Kasatochi Volcano in Alaska. This plume is moving north and currently situated over North Dakota and western Minnesota according to the NOAA HMS text.