I imagine this is what the dinosaurs experienced. Not 45 minutes ago, we arrived at a lake just a few miles from Cloud’s Rest in Yosemite. We had set up a hammock, chairs, and relaxed into the beaming afternoon sun.
Then, someone turned on the cloudy gray setting, sequestering the sun, and started sprinkling ash on us as a prank. We packed up in haste, found camp, pitched our tents, and spent the majority of our lazy afternoon playing liar’s poker inside our tent. The smoke suffocated our moods as we considered wrapping up our trip and heading home, only three days into a week long backpacking trip.
The next morning, it looked as if someone emptied a fire pit on our tents. Ashen makeup glossed the alpine lake, clogging our water filters. Despite our somber environment, we chose to stick with our plan to hike up Cloud’s Rest that morning.
We hiked as the sky slouched with gray clouds as if a downpour threatened. No rain was coming.
An empty summit surprised us. Recent California wildfires and smoke muted the usual throngs of Saturday hikers. After the jubilation of summiting, we took in the views with trail mix, dried apricots, and turkey jerky.
Instead of postcard vibes, we were entranced by a smoke signal floating across our view like a low San Francisco summer fog. Orange lights flickered. A wildfire, just getting started in the distance.
Not fog and not rain clouds...
I wrote about how California wildfires will worsen if we don’t take action. There are two policy options to address the megafire threat: (1) do controlled burns to clean out dead firewood or (2) continue to sequester fires, preventing natural burn, and allow nature to dictate record-breaking wildfires.
Either scenario means more smoke and days with poor air quality. The second scenario means more off-the-chart days, like 2020 wildfires turning San Francisco to an extended cut scene from Blade Runner.
PM 2.5 is fine particulate matter most common during wildfires. 2.5 indicates microns in diameter, so anything less than 2.5 microns is PM 2.5. For context, a human hair is roughly 50–70 microns in diameter.
So these are the smallest and lightest pollutants. As a result, they stay in the air longer, increasing the chances we breathe them in. Alveoli air sacs in our lungs are responsible for oxygen exchange and our lungs interact non-stop with the outside world. Combine these two and this is how fine particulate matter enters your lungs and blood stream.
For adults, PM 2.5 is a cause of all sorts of issues from heart disease and decreased lung function. In our children, it affects all stages of development and overall lung health[1].
The World Health Organization’s guideline for PM 2.5 is 10 µg/m3 annual mean and 25 µg/m3 24-hour mean. If you map that to the Air Quality Index (AQI), it corresponds to an AQI of less than 50. In the San Francisco-Oakland-Hayward region, well over one third of days last year had an AQI greater than 50.
Exercising outdoors means faster air exchange. Exercising in poor air quality means pollutants enter our bodies at a faster pace.
Last year, there were stretches of days well above AQI scores of 300. We acclimated and thought, “hey, AQI is 100 outside, it’s not too bad, I can go for a jog”.
Don’t make that mistake! Stay inside with a HEPA air filter. Take it from the very smart people that slept outside while wildfire smoke blew into their faces.
As the afternoon crawled on, we were the only ones left on the peak. We decided to stay the night on the summit of Cloud’s Rest. With wildfires and smoke, we had the summit to ourselves on a Saturday night. When do you get a chance like that?
The setting sun looked like the last day on earth, spooky with a hazy orange beauty. We ate an apocalypse appropriate last meal: a dehydrated feast of chili, mac & cheese, and Pad Thai noodles. Satisfied stomachs sank into chairs as the air filled with the hum of the harmonica. Only mental tension broke the calm as we continued our liar’s poker battle.
We brushed our teeth as ash continued to fall, a funky combination. It felt as if we were inside Nature’s home while it was on fire, sleeping top bunk on the highest floor. Smoke filled the house, collecting near the ceiling where we slept.
I tossed and turned throughout the night, wondering if it would actually be possible to suffocate from this type of smoke exposure. With an N95 mask strapped to my face, I drifted off to sleep.
The next morning, we woke up to high definition blue and a vibrant morning light. Winds shifted overnight, blew away the nightmarish 24 hours of smoke around Cloud's Rest, and we were rewarded with an improved view of Half Dome, El Capitan, and Yosemite valley.
With this knowledge about wildfires and PM 2.5, I’m not sure I’d do it again. Next time, I’ll stay indoors to watch Free Solo on Netflix with my HEPA air filter and indoor air cleaning plants.
[1] World Health Organization’s study of pollution on children’s health.
Edit: The World Health Organization revised their air quality guidelines on September 22, 2021, the first time in 15 years based on new evidence. The threshold for "good" air quality were halved.