We’ve had heavy smoke today, from BC and the NWT fires, I assume. Air quality is rated at 11, which is a “High Health Risk” according to the Environment Canada scale.
It’s also been raining all day, quite heavily mid-afternoon, tapering off now.
Does rain affect the smoke in any way? Does it help bring the amount of smoke down?
In general yes. The soot particles get trapped in the raindrops and fall out. Soot and other fine particulates can actually act as seeds for rainfall but providing the “condensation nuclei” needed to start the process of condensing water vapor into first microscopic, then macroscopic drops.
If your rain is unusually vigorous versus the rest of the cloudiness I’d lay that vigor on the smoke. And the rain will wash a bunch of it out. Sadly, that stuff all ends up on the ground or in the waterways as real fine dust. So it won’t necessarily stay out of the air, but it’s out for now.
Interesting, thanks.
The rain has ended now, but the smoke in the air is still there. Maybe not as thick as it was in mid-afternoon, but at least not so smoke-smelly.
Anecdotal story - we tourists were in China over a decade ago. We arrived in Shanghai during a light drizzle, and the air was clean the next day. We did not realize until a few days later that it was reverting to its normal state, a haze like fog. We got to Xi’an and my first question - being from Canada - “is there a forest fire nearby?”. No, it was the pollution. the same thick haze was evident in Beijing when we arrived, and even pervaded the Great wall more than 60km out of town. Then, a day before we left, it rained - and we were surprised to see that Beijing had mountains in the distance.
Yes, rain clears the smoke and haze. But the effect is temporary. Very temporary.
I had a similar experience in New Delhi. There were only a few days when the sky was completely clear. That was caused by brisk winds.
The first thing I noticed when I got off the plane was the smell of smoke, and then saw the perpetual haze.
Anecdotal story #2
Was in a trip across northern USA a month ago.
On the section from Sioux Falls, SD to Custer, SD visibility from the Canadian smoke haze got down to a couple of miles. Crossing the Missouri at Oacoma you could barely see the other side of the Lewis & Clark bridge.
We go a hefty fall of rain that night in Custer and (once the morning fog lifted) the air was clean and smelt fresh. Through the afternoon the haze and the smokey smell started to come back, though much reduced.
Already answered, but I’ll further point out that rain is so effective at cleaning the air that industrial wet scrubbers use the same operating principle to clean exhaust gas streams:
I thought I read somewhere (I cannot find the article now…I tried) that very large forest fires create their own weather and can create rain. A LOT of water is being boiled off when trees burn (not to mention a byproduct of combustion is water…it’s all gotta go somewhere). The heat from the fire tosses that water up into the atmosphere. What goes up, must come down. So, in a way, the forest fire produces its own air scrubbing system somewhere downwind. Not 100% on that though.
It could happen:
This. When I lived there I used to refer to New Delhi as Old Smelly.
And thermal inversions make the pollution even worse. I had an apartment on the 4th floor of a building. During the winter (which can be quite chilly) I could look out from my balcony and see a column of smoke from someone burning leaves for heat rising straight up and then leveling off when it hit a layer of warmer air. Pretty neat.
But occasional winter rains definitely helped clear the air.