Fog to Smog

Let me describe this slideshow up front so you know what you’re seeing. All but the last photo was obtained on Superbowl Sunday, Feb 1, 2015. That game was held at University of Phoenix Stadium (UPS) in Glendale, AZ. Photos were taken from my front deck, which has a view of Phoenix and Glendale to the south.

  1. Phoenix at 0700, showing a layer of dense fog over the city.
  2. By 1200, much of the fog has been “burned off” (evaporated) by the Sun.
  3. By 1500, that white fog is being replaced by smog, a visibly different brownish color.
  4. By 1900, the smog reached a level that triggered an air quality alert.
  5. The inset shows UPS, 27 miles away, just barely visible through a saddle in the mountains.
  6. The reverse view, from UPS looking back to where I was shooting these photos.

Conditions that day were perfect for an inversion, with cool moist air near the ground and hardly any wind. Because the Phoenix area is more or less surrounded by mountains, a layer of air can get “trapped.” The tight capping of the fog layer, confined to about 200 meters (600 feet) AGL, is visual evidence of an inversion. The layer of smog that formed later visibly tops out around 1000 meters (3000 feet) AGL, but gradually diffuses with altitude. This tells us the inversion has broken and air layers are mixing properly.

Add bright sunlight (and its UV component) and you have a recipe for smog. And of course, Superbowl Sunday brought a huge increase in vehicular traffic, as well as an increase in cooking at food vendors and backyard barbecues. Fog contains small droplets of water that can act as reaction sites for smog-producing chemistry. We don’t get fog very often in Phoenix, but a recent rain supplied the humidity for its formation.

Here’s some (unbalanced) chemical reactions that take place under those conditions, all with unhealthy byproducts:

  • In the high-temp internal combustion engine: N2 + O2 → NO (nitric oxide)
  • When vehicle exhaust meets atmosphere: NO + O2 → NO2 (nitrogen dioxide)
  • In the atmosphere: NO2 + sunlight → NO + O+ (photolysis aka photo-dissociation) ⇒ O2 + O+ → O3 (ozone),
  • and: NO2 + O2 + sunlight + unburned hydrocarbons → CH3C(O)O2NO2 (peroxyacetylnitrate w/ CH3 methyl group)

These reaction products are harmful, especially to people with breathing disorders like asthma and COPD. Concentrations on the order of ppm (parts per million) can cause problems, and will trigger air quality advisories or alerts. How bad it can get depends largely on the vehicle emission guidelines (and compliance) in your area.

Phoenix gets these alerts frequently during the winter, and declares “no burn” days that restrict the use of fireplaces, outdoor grills, lawnmowers, and leaf blowers. I’m located about 300 meters (1000 feet) higher up than Phoenix, so unless the wind is blowing from the south, the smog doesn’t reach me. Still, when I have to drive into Phoenix for business, I often return with stinging eyes, congestion, and a scratchy throat. It’s nice to know the science behind smog — unfortunately, that knowledge confers no immunity.

In case you missed the big game, the New England Patriots beat the Seattle Seahawks 28-24. IMHO, the Green Bay Packers should have been there instead of Seattle. But I digress. This was Superbowl XLIX (49). Interestingly, the next one will not be Superbowl L (the following Roman numeral). Instead, it will be branded Superbowl 50. After that, they’ll return to Roman numerals: Superbowl LI, LII, LIII etc. Apparently, the league didn’t think “Superbowl L” had enough visual impact. Thankfully, their decision also spares us the word-play of how “it’s gonna be an L of a game.”

Next Week in Sky Lights ⇒ Strange Cloud Explained

February 20, 2015 Triple Conjunction
Strange Cloud Explained