While yesterday did not have the drama of the prior few days, there was aerosol drama anyway, a real battle took place against the forces of evil, represented by air loaded with urban smog, and good, clean air to its north, in which we were initially immersed.
A rare fog bank streamed out of Tucson toward Marana, Continental Ranch, and south Oro Valley and beyond. The moist air near the ground associated with our recent deluge, and capped by an inversion, combined with very light winds allowed fog to form in the first place. Its westward trajectory into the southern reaches of Oro Valley is associated with the normal sloshing of winds in Tucson, from southeast in the morning, to northwest in the afternoon on “undisturbed” days. On most mornings, all we see is a haze layer close to the ground that streaming out of Tucson down that way. In this case, the smog layer was in the form of fog, droplets wreaking with all kinds of untoward particles and chemicals like sulfates, nitrous oxides, hydrocarbons, etc., these from cars, wood burning stoves, factories, etc, all the things associated with modern life in an urban center except for wood burning stoves. As a smog-containing fog, it was pretty, however.
However, most of the time, maybe nine out of ten, that thin smog layer stays south of Catalina, can’t quite get here. But yesterday, the forces of evil resulted in an advance of the smog-fog to Catalina. A southwest wind came up in mid-morning, and like a tidal wave, that low thin layer slurped its way up the Catalina Mountain sides and Oro Valley, rolling over everything, growing deeper as the long absent sun warmed the ground, dissipating the fog, leaving the aerosol contained in it, “naked”, as it were.
It seemed for a time that a slight north wind might rule the day, and the smog would stay south of us as it usually does. Instead an ugly southwest wind developed, as often happens here in the afternoon, as air starts rising off the Catalinas to form Cumulus clouds.
And that’s part of what happened yesterday to bring us smog, besides us being in the protected lee of the Catalinas due to northeast winds aloft. When you’re in the lee, sometimes moisture and aerosols remain trapped there, like those cattails I used to pop open at the north entrance of the University of Washington’s Atmospheric Science Department on days with a strong southwest wind and those seeds would circulate in the lee for maybe an hour in really interesting swirls that could be seen due to all the seeds floating around and around, incoming people waving their arms to get them away because they would stick on your clothes. I was younger then (40s maybe), and I guess it was pretty childish. I’m not like that today, as demonstrated by this blog. I wish I had some cattails today, though.
No rain in sight.