Worried about air pollution from wildfires? Here are 3 things you can do.

The tragic recent wildfires in the Napa and Sonoma county areas have caused school shutdowns and warnings of “unhealthy air quality” throughout the San Francisco Bay Area.

As someone who lives in Beijing most of the time, dealing with particulate air pollution is a fact of daily life, so I’m going to provide some practical tips for everyone here.

Sunnyvale, CA on October 11, 2017

Tip #1: Don’t run a marathon, and certainly not outdoors

This one is obvious but is worth stating: when the air quality is poor, you don’t want to be breathing all that stuff in, and you especially don’t want to increase your respiratory rate by going for a difficult run. Now, running indoors on a treadmill may be marginally better, but I still wouldn’t recommend it.

Why is that? The “standard” guidance is that people should stay indoors when the air quality outside is unhealthy. This sounds good in theory — after all, walls and windows should keep bad air out, right? The problem is that small particulate pollution actually gets into indoor spaces extremely easily. In fact, most air conditioned indoor spaces reduce the particulate concentration between 20–40%. Better than nothing, but certainly not great. So what should you do if you have asthma or have family members who fall into the sensitive category? Read on.

Tip #2: Don’t bring in outside air

If the outdoor air quality is bad, you should close your windows and keep them closed. If you’re in your car, you should use the recirculating interior air option. I did a quick test today, and the cooling + recirculating air option on my rental car (Hyundai Sonata) provides about a 75% reduction in particulate concentration in about 10 minutes. In fact, 75% reduction is about as good as it gets without utilizing really fancy methods.

Tip #3: Buy an air filter or make your own

Air purifiers work. But typically you need a fairly large fan + large filter in order for them to work well, so when the air quality index exceeds 150 (as it has in the past week in SF Bay Area), it is likely that a desktop unit with CADR ratings of 80–90 will be inadequate for bedrooms. For reference, on normal days in Beijing, for my 700 square foot apartment, I often run two units with CADR > 150.

Also, you might have a hard time finding an air purifier. I certainly did when I visited my local Target store yesterday:

So what you do if you can’t find an air purifier?

For small spaces, you can make your own. This method is inspired by the good folks over at SmartAirFilters.com who really popularized the “Fan + Filter” DIY method. I did something similar that cost me ~$40 USD.

Here’s what I used:

  • One Filtrete Healthy Living filter
  • One Box Fan (approximately similar size)
  • Some tape / rope / something to mount the filter on the fan
you should end up with something like this

Voila! There you have it. Your very own DIY air purifier. It’s a bit noisy, but nothing unbearable. And does it work? Sure does! I have data to prove it.

I started by opening my windows to ensure the maximum amount of pollution was available in the indoor space. I then closed the windows and turned off the bathroom exhaust fan, and turned on the DIY air filter unit to low speed. Readings were taken at approximately 1–2 minute intervals in my ~300 sqft hotel room.

Oh, and if you have a central heating/cooling system, you should be able to install a HEPA filter at the intake recirculation / output vent.

Feel free to comment or ask me questions below.