Tuesday, September 18, 2018

Why is autumn air so wonderful?

I can't tell you how many people have commented to me the last few days about the wonderful quality of the air they are breathing.   Some are almost exultant, describing their pleasure in inhaling air that is brisk, clean, and cool---just perfect.    It is true--their is something about autumn air that is wonderful. 

So let's check on some of the characteristics of the air we are enjoying today.

First, it is clean---really clean--with the smoke of summer a distant memory.

For example, the particulate level (PM2.5 small particles that are bad for your lungs) is way down, as low as it goes around here (see plot since June 1 below).  Other pollutants, like low-level ozone, are also down.

With a lack of particles, the sky has been very blue, when the clouds were not there.  The image from the Seattle Space Needle Panocam shows the azure skies.  Blue skies and sun are a psychological plus, even for cloud-accustomed Northwesteners.

What about relative humidity?  According to a number of studies, the optimal relative humidity range for human health is around 40-60%, with low relative humidity promoting flu and breathing problems.  No problem.  Ou relative humidities the past few days have rarely dropped below 50% and have been around 50-60% every afternoon! (see plot below for the past 12 weeks)

Cool, crisp air is a pleasure for the lungs, but not too cold.  The plot of air temperatures at the UW for the last 12 weeks shows our perfect situation the last few days.  High temperatures in the mid-60s, but with temperatures only dropping into the mid-50s.  Ideal.

And there is something else, some essence of fall air that I can not describe with available numbers--some aroma from the falling leaves, a smell of rain on the previously dry ground---you know what I mean.

Clean, cool, unpolluted air of the proper humidity.   Fall is here...time to take a deep breath.  And time to appreciate living in one of the rare locations where it all comes together in such a wonderful way.


  1. Thanks for putting into words the feeling I get in the fall from light hiking with my small dogs at Westcrest Dog Park. It has been stunningly wonderful, a great way to get those 10,000 steps in with a couple of flop eared friends.

  2. Yes, it's fresh, if a little sad, with the rapidly waning daylight. I do like to see rain. The trick is getting sun and rain in the same month.

    But the ground is still dry a few inches down. We need yet more rain.

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  4. We moved to Whidbey two years ago (from the Midwest). Mornings through the fall and winter on 2016-17 (and since) we have woken to firs swaying in the breeze and the clean, fresh PNW air blowing overhead through the open windows. Sometimes just laying in bed for 20 minutes soaking it all in. All the while being thankful not to be breathing in raw, polluted midwestern air. A total delight!!!

  5. Thomas, how'd you like the forest fire smoke blowing in through your windows over the past three years? It's all relative, and if you live near the Great Lakes you don't experience much air pollution anymore.

    1. Eric, the smoke certainly was a bummer this year. It wasn’t as bad on Whidbey as I think it was in Seattle. Still it was a health concern and worrisome as a potentially routine event in years to come.