Not So Ideal Weather Using ‘Ideal’ High School Chemistry

I hope my reference to High School Chemistry didn’t conjure up painful memories from your past; a la exploding graduated cylinders, or brutal Bunsen burner burns.

If not, please read on with an open mind.chemistry_book

Very basic chemistry explains why the Willamette Valley has been cold, foggy, gloomy and literally unhealthy for those with certain respiratory conditions.

So here comes the ‘hard’ part. Take a deep breath as I now present to you a very simple equation fundamental to science. Does the Ideal Gas Law ring a bell? All of the gasses we deal with in our atmosphere can be described using this handy equation.

P = ρRT

The simple relationship says. The pressure of any gas (P) is equal to the density of the gas (ρ) times the gas constant (R) times the temperature of the gas (T)

Okay, if you’ve made it this far the rest is easy.

Using simple algebra we can easily  rewrite this equation as such:


Since the gas constant (R) doesn’t change – (duh it’s a constant) we can easily rearrange this to read:

ρ ≈P/T

This is an elegant little expression. It can be read like this: The density (basically the weight) of a gas (our air) is inversely proportionate to it’s temperature. Since our air pressure hasn’t changed much, it’s easy to see that the colder our air is (T), the denser it is as well (ρ). 

This relationship represents  the cornerstone of our weather lately.

The cold dense air is heavy and is resting right on top of us  in the lowest parts of the Valley. Since there are no buoyant forces to make this air rise, all of the dust, ash and other particles are trapped in this shallow dense air. We call this stagnant air. The longer this stagnant air sticks around, the more pollutants it adds. It’s kind of like adding a bit more salt to your soup day after day.

It’s unfortunate, because we have a giant ridge of high pressure aloft which would ordinarily give us unseasonably warm, sunny weather. Look at the temperatures on the mountain lately. 53 at Mt. Hood meadows today, 60s in the Coast Range. The low January sun angle isn’t strong enough to warm this layer up so it becomes less dense and lifts away. There is also little evidence of a major pressure change (AKA wind) to help move the gloom.

So here’s the real kicker: we may have to wait for rain to make us sunny again. How the heck can rain make it sunny you may ask?

Well, rain would mean an area of low pressure would move above us, it would also cool the atmosphere from above thus restoring the atmosphere back to equilibrium. A state where the temperature decreases with height, or the exact opposite of an inversion.


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