Air Quality Suffers with Northwest High Pressure and Skier's Hope

There has been a lot of  talk about the West Coast drought, particularly with its impacts on mountain snow pack and future water resources.

But the persistent high pressure over the eastern Pacific that has caused the drought is also having another effect:  creating low-level inversions and reducing air quality in many Northwest locations.   It has also made this a particularly foggy fall/early winter.

As an aside, one unfortunate side effect of  the persistent fog occurred on New Year's Eve with FogFireworks, where the upper portion of the display  at Seattle's SpaceNeedle was either invisible or muted for much of the performance.

 Picture courtesy of KING-5 TV Seattle

In December at Seattle-Tacoma Airport, 20 of the 31 days reported fog, many with dense fog. 16 days with fog in November   And who can forget Fogmageddon in October?   I can't tell you how many people have complained to me about the persistent low clouds this year.

The villain has been the persistent high pressure ridge over the eastern Pacific, like this one that occurred at 1 AM on January 1st (upper level, 500 hPa map shown).  You see how the height lines bulge northward?  That's the ridge.  At low levels this is associated with high pressure.

Ridges cause inversions and stable air in two ways.  First, strong sinking with high pressure aloft causes warming above the surface.  High pressure produces clear skies aloft that allows good radiational cooling at the surface.  And high pressure usually brings light winds, thus very little turbulent mixing of air at the surface.   Heat above, cool below, and don't mix....what do you get?

An inversion in which temperature increases with height! 

 Inversions are very stable situations that prevent air from mixing with height.   Pollutants concentrate over time near the surface and as air cools near the surface fog often forms.  This has been the story of much of our fall and early winter.

So what has the air pollution situation been around here?  The Puget Sound Clean Air Agency has a wonderful website where you can plot pollution data from around the state.  Let's take a look at the amount of small particulates (smaller than 2.5 microns, called PM2.5) at a few locations.  Such small particles are quite nasty, capable of being drawn deep into your lungs where they can lessen your respiratory capacity, initiate asthma attacks, or cause heart attacks.

Let's start with Lynnwood, north of Seattle.  The biggest spike of bad air:  July 4th!   You notice that air quality is far better during the summer than during the winter.  That makes sense;  no need for heating during the summer so less combustion byproducts.  And inversions or stable air situations are more frequent during the cooler season with the long nights that allow strong surface cooling.  But this fall was clearly particularly bad, worse than last fall/winter because of the persistent high pressure and inversions. (the previous year is also shown)

Going south to Lake Forecast Park, a location with a significant air quality issue, we see the same pattern, if not worse.  This fall the air quality has been particularly bad...not Beijing or Shanghai bad, but noticeable.

I could show you sites in Seattle, Tacoma, and elsewhere west of the Cascades but the story would be similar.

As long as we are talking about air quality, here is an interesting fact:  air quality varies substantially during the day.  To illustrate, here is a plot at Lynnwood for the last week or so.  Many days have an identifiable peak during the evening hours, a drop during the early morning hours, and a rise during the afternoon.

Makes sense.  Folks turn their heat down at night.  Warm the house for only a hour or so in the morning before heading to work or school.  Turn it up later in the afternoon or early evening.  Also meteorology helps such a pattern, with the atmosphere stabilizing during the late afternoon as the sun declines and the surface cools.  So try to do most of your breathing during the day.  Clearly, a better time for strenuous exercise if you worry about the quality of the air.

SKIERS REJOICE

      A major circulation change may produce substantial snow in the Cascades later this week:  here is the 72h snow totals ending 4 AM on Saturday.  Several FEET OF SNOW

Fracking and Ozone

UW Professor Becky Alexander has established a page on the Microoryza crowdfunding web site that outlines her project  to understand why natural gas fracking often leads to high ozone values over snow (go here to see it). If you want to learn more about this important project and how you can help it happen, check out the web site.  She is now at 52% and will get nothing if she doesn't reach 100%.  So if you know folks interested in the fracking issue, please let them know about this.