Here are 4 webcam views of the dirty air this morning (31 May 2013) with the views looking (from top to bottom) north, east, south and west. Mountains were partly to totally obscured when I walked at sunrise.
I went to the Air Resources Laboratory HYSPLIT trajectory page to examine the questions of where did this dirty air come from and where will it be heading today. All the trajectories I explored (all from the NAM 12 km forecast data base at 00 UTC last evening) indicated that the low-level air (below 1000 m agl) over the Tucson metro area this morning originated over northwestern Mexico. The trajectory plot below shows where the model forecasts air parcels to move to during the next 18-hours. Each trajectory begins at 500 m over TUS airport and a new forecast begins each two hours today, starting at 12 UTC this morning (a bit before the photos shown above). Some of the dirty air makes it all the way back into Mexico. However, much of it loops around during the period, remaining trapped over Santa Cruz and western Cochise Counties.
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