It’s hot but it’s hazy too. Should I run the fan tonight?

Smoke and ash from the Norse Peak Fire created a haze in Tacoma and throughout the South Sound.
Smoke and ash from the Norse Peak Fire created a haze in Tacoma and throughout the South Sound. jbessex@gateline.com

The drift of forest-fire ash across Puget Sound skies has a bit of a bright side: though uncomfortable, it isn’t nearly as bad for you as what fell after the 1980 eruption of Mount St. Helens.

The foggy haze that settled across the region Tuesday was “a lot like regular weather, except with smoke,” a Puget Sound Clean Air Agency spokeswoman said.

Large ash came down, which is a better outcome than if the high-altitude, fine-particle haze was at breathing level.

The specks and flecks that fluttered through the region’s — and nation’s — air after the Mount St. Helens eruption were composed of sharp minerals. Gov. Dixy Lee Ray warned the ash flakes were half silica, a glass component.

“Hence they’re very sharp and needle like and can cause physical damage to the lungs,” Ray said in a May 1980 address to the state.

She went on to warn those who must be outside to “wear a face mask at all times when there is ash in the air.”

South Sound runners and bicyclists plied ahead through the crud, as did at least one expert on the scourge of our skies.

University of Washington professor Dan Jaffe, chairman of the physical sciences division at UW-Bothell, rode his bicycle to the office Tuesday morning while the ash flakes accumulated like early snow on buildings and cars.

Q: You biked to work in this?

A: It wasn’t this bad when I came in. I’m not biking home. I’m taking the bus.

In the morning (Tuesday), it was about my threshold, getting to work at 8 a.m. Now, I’m measuring the particulate concentrations at UW-Bothell and we’re getting about 40 micrograms per cubic meter. That’s not a good thing to exercise in.

Q: What’s in this ash we’re getting?

A: The ash is typical ash from a wood fire.

It’s a very high concentration of inorganic elements that don’t burn as well. It’s potassium and calcium carbonates, largely. It’s not that dissimilar from the ash that’s left over in your fireplace after you burn logs.

Q: We tend not to roll around in that. Is it terribly dangerous to walk around in?

A: I wouldn’t say it’s dangerous.

The bigger health concern is the finer particles in the haze you see. Ash is actually this large particulate matter. We don’t breathe it in very efficiently; it’ll get caught in our noses. Now, that isn’t a pleasant thought, but it’s better than having it get into your lungs.

The ash particles could be anywhere from a tenth of a millimeter to a couple of millimeters. This morning, I saw a couple that were 2 mm. You’re not breathing those into your lungs.

Q: What should I be worried about?

A: What is important, when you breathe it in, is the much finer stuff.

I biked along Lake Washington; when you looked across at the haze and saw it obscuring the sun, those are the fine particles. They are less than 1 micron in diameter, smaller than a human hair. Those are the ones we breathe in.

Q: How severely should we worry about those, since the effect is sending ash across our region in a way we haven’t seen since a volcano erupted?

A: If you were under the plume of Mount St. Helens, the ash was from volcanic rocks. That’s quite a bit more damaging than the ash from a fire plume.

Interestingly, the ash that’s falling is rather different from the fine particles now. The fine particles are carbon and soot, like coal dust almost, or like diesel smoke.

Q: That isn’t comforting. How do we best cope?

A: It’s going to be a hot night, and like a lot of people, I cool my house with fans in my windows.

Tonight, I’m not going to be running the fans. I’m just going to have to put up with extra heat in the house. Close up your house. Now, that’s going to make it warmer. That’s the trouble. Tonight’s not going to be the nicest night.

Q: What’s the best way to get this wood ash off our walls, windows and cars, once the wind shifts?

A: You should be good with soap and water.

I wouldn’t try anything too exotic. Vinegar would be good ... if soap and water doesn’t work.

Derrick Nunnally: 253-597-8693, @dcnunnally