If you got up today, or even late yesterday afternoon, and got a feeling that the sky was “not right”, you were right! We have a well-mixed smoke layer above us, “well-mixed” meaning you don’t see any gradations in it. That in turn, means its been up there for a LONG time, and the gradations have been mixed away by turbulence. (If it was from a fire even as close as California, you would probably notice thicker and thinner portions of the smoke.)
Where did the smoke layer over us come from?
Probably from northern China or Russia. Haze can be lofted to high levels and then can race across the Pacific to the West Coast and beyond in the jet stream. Sometimes its even dust, but that’s a little more unusual than smog, that is, smoke and haze from regular pollution from urban areas and fires.
Below are backtrajectories for the air over Tucson ending at 5 PM AST yesterday afternoon just as the smoky air was arriving over us. That was the latest global dataset available for this calculation from NOAA’s Air Resources Lab. Estimating that the smoke layer is at 16,000 feet or higher, backtrajectories for three levels above the ground are shown, ones between for 16,ooo, 22,000 and 30,000 feet above the ground. The calculation goes back four days (96 h). The star is where the air trajectory ends, over us. (Note: you can make these yourselves, BTW, at the ARL site using their Hysplit model.)
You can see that the air over us yesterday afternoon, and certainly today as well, came from Asia. The model thinks the haze layer was already at a high level (look a the height of the air four days ago in the lower elongated graph) while exiting Asia. So, this smoke layer is no doubt from even farther west east Asia
BTW, if you were on a plane departing or arriving in Tucson yesterday or on one today, you would doubtless pass through this smoky layer and see it as a thin black or dark brown line. Maybe you could ask a stewardess to ask the pilot or pilotess or his/her many helpers up front to tell you the level at which he passes through the thin dark line. I would, certainly. But usually nothing happens…. Oh, well. Below some “just in shots” of the not-so-blue-sky. The whitishness of the sky is caused by “forward scattering” of the sun’s light off the tiny aerosol smog particles. “Back scattering” from these particles, when you look at the sky opposite the sun, is pretty nil with smog particles, and so the sky doesn’t look quite as whitish as toward the sun, but its not the intense blue we should have.
Yes, we are a global community of smog producers, and here is one example.
The End.
