Growing up in Chicago means you become accustomed to days on end of kind of dingy brown air.  Those special days when the brown air cleared away and everything was outlined in sparkling light were greeted with happy sighs and delight.

If you grow up with this atmosphere, it seems "normal" to you.  It wasn't until the OmegaParentalUnits moved to the Southwest and I took to visiting them that I realized that many places do not have that continual dingy brown blanket.

When the OmegaBro lived in Hemet, California, we would drive out west to visit on a semi-regular basis.  We would drive through crystal clear desert landscapes, where the heat caused shimmering mirages over endless salt flats.  Then we would come up to the mountains and start driving through them.  As we got closer and closer to the L.A. metro area, we would see these sinuous snakes of dingy brown floating through the canyons, the smog of L.A. infiltrating outwards.

Typically, those brown tentacles of smog were low; they didn't pour over the mountaintops, but slithered below a certain altitude.

Similarly, when I would visit Chicago via airplane on sunny autumn days, as the plane approached the metro area, I would see a bowl of brown smothering the city...and as the plane made its descent, we would be plunged into the brownness.

The really bad days, like those autumn days in Chicago, are the result of inversion layers.  In an inversion layer, rather than having the normal warmer-air-sits-on-the-ground-with-colder-air-above-it, you have colder air close to the ground, with a layer of warmer air acting like a lid above it.

In the autumn, Small Mountain University Town and Hippy Dippy Enclave in the Woods get inversion layers.

What happens then is that, when it rains, the night is filled with thick fog.  If it's cold, and people fire up their wood stoves and fireplaces, the night is filled with thick smoke.  I have had mornings when I woke up, peered out the back door, and seen grey smoke filling the air as far as I could see.  The first year we lived here, I panicked a few times, thinking that there was a fire in HDEW.  Before I knew about the fire monitoring websites I could visit, I actually called the local fire station (two blocks away) to timidly inquire where the fire was.

Then there's the added factor of prescribed burns.  ("Prescribed burns" used to be called "controlled burns".  Then there was the disastrous fire at Los Alamos, the result of a "controlled burn" that, alas, quickly became uncontrolled.  [As an aside, my feeling is that any controlled burn that is started on a red flag warning day is a piece of total idiocy.  There were rumors at the time, quickly hushed up, that it was the result of DC folks overruling the locals--I don't know if it's true, but, frankly, given that the locals know what red flag days are like, it seems mighty unlikely to me that gummint folk who had acted as forest rangers in that area for 20 years and more would be willing to actually proceed with the burn as scheduled.])

Autumn is peak prescribed burn season around here.  The fuel wood is generally moist, so things won't spread.  Usually, there's low wind, or no wind.  Typically, it's cool.  And, typically, these conditions produce an inversion layer overnight.

Which means that we drive into town through dense, thick smoke.  Enough so that we have to close all the car windows and set the ventilation system to recirculate, rather than draw in outside air.

So.  Smoke gets in your eyes.  And your nose.  And your lungs.  And you start to sneeze.  And cough.  And your eyes water. 

Thank heavens those inversion layers usually lift by mid-morning.  The air clears, the smoke blows away, and we get our crystal-clear depthless blue sky back again.

Technorati: Prescribed burn, inversion layer, Los Alamos