In the last day or so there was a small thread in BorisGr's log concerning air quality/pollution during the summer. I thought the following EPA air quality site would be of general interest.
EPA AIRNow
Of particular significance is the hourly reports. In general, the worst time to run is in the late afternoon and evening. Conversly, even on orange/red days, the morning is still green. Because of that and the Dallas heat all my workouts shift to the morning hours during this time of year.
And it should be noted that while there are no reports from WY, that is only because the gov. hasn't yet establish badger-odor safety levels, which, whatever they are, are certainly exceeded in most WY towns.
Today in the big-D: high of 94, with "red" level air. Wonderful... not.