Last updated: August 19, 2020


I first wrote this doc in response to the horrendous air pollution/smoke in Seattle/Vancouver in August 2018.

This doc should be applicable to residents of other cities experiencing similar problems in different time periods (i.e. SF Bay November 2018, Oct 2019, Aug 2020)

I’m not an expert (though I was interviewed on TV recently 😛), but I’ve lived one year in eastern China in 2013 and part of this summer in Paris (air pollution is not just a developing-country phenomenon), so I’ve dealt with my share of air pollution and done my research.

Want to discuss/comment on this doc? Go to the commentable google doc here.

Want to reach me directly? Probably best to send me a tweet.

Disclaimer: Some of the product links in this doc are Amazon affiliate links, which means I receive a few percentage points of the product sale price if you do buy the product. My primary motivation for writing this doc is public education (in 2018 I took all proceeds and put them into running google ads for the website to promote awareness), and I only intend to use the proceeds to fund upkeep and future improvement costs to this site (maybe upgrade from a low-tech google doc at some point  😛). If you’re not comfortable with supporting this site in this manner, just clean up the Amazon URL after you click through.

Finally, obligatory legal disclaimer: the information contained in these topics is not intended nor implied to be a substitute for professional medical advice, it is provided for educational purposes only.

Okay, let’s go to the actual information you came here to look for!

2-minute Summary:

What’s happening? What is bad about this air pollution?

If you’re reading this, you probably know what’s happening. Wildfires in Washington State + British Columbia  has led to Seattle, Portland and Vancouver being blanketed in smoke on and off for the past few weeks

Here’s an article that examines this more in detail:

There’s a link between climate change and these wildfires becoming more frequent and intense:

The primary danger of the air pollution from wildfire smoke is from PM2.5 (particulate matter smaller than 2.5 micrometers). These particles are especially dangerous because they can be absorbed into the bloodstream, causing inflammation, cardiovascular problems and other short-term and long-term health issues**. More info here: 

Other pollutant components of air pollution include:

PM2.5 and PM10 are categorized as particulate pollutants and can been filtered easily given the right equipment (see below)

Gas pollutants however, are trickier to filter, as we’ll see.

Here’s a good overview on the types of air pollution

The EPA has standards on levels of various air pollutants considered acceptable: (thank you Clean Air Act!)

**Common misconception is that particulate matter’s effects are primarily on sensitive populations and on the lungs, but more and more studies are are showing that the effects even at low levels on health young people are real and causes inflammation in the short term. Here’s a good overview article: Here’s a twitter debate I’m attempting to have with a UW physician who claims that the pollution is just fine for most healthy people.

How to deal with particulate matter- masks and HEPA filters

Fortunately there are some easy ways to deal with PM2.5 and PM10 pollution:

1. Wear a mask when outdoors

I recommend this 3M N95 mask ($20 for a 10 pack on amazon). Make sure to fit it properly (note this video shows a valveless model, but same fit instructions apply). Here’s another way to check if your mask fits properly**.

This mask in particular I recommend for several reasons:

I’ve seen a lot of Seattle-ites wear bandanas or surgical masks. These provide *some* protection, but really, you should just spend the $2 and get 99% particulate protection.

If you’re worried about looking weird, come on, this is Seattle, we’re very accepting of eccentricities :-P.

Worse case, you’ll get caught by an AP reporter in Gasworks park and be interviewed for national radio/TV 😛

I wore a mask some of the time when I was in Paris, fashion capital of the world, earlier this year, and hardly anyone batted an eye. In fact some friends wanted to take selfies with me :)

Oh, and when to wear a mask? I typically use this app, which gets data from various government feeds, and wear a mask if PM2.5 surpasses 25 μg/m3 (10 μg/m3 if you want to be conservative). 25 and 10 are the World Health Organization’s 24-hour and annual guidelines, respectively.

If you wanna be extra lazy, you can just follow the app’s advice and wear a mask when it recommends you to, but I don’t really trust the AQI conversion scale and prefer to use the raw PM2.5 numbers to inform my decisions.

Here is an Economist article on why air indices tend to underreport the harmful effects of pollution

**A lot of physicians will claim that these masks are useless unless fitted professionally. That's not really the case. Two separate fit tests by Richard Saint Cyr and Thomas Talhelm have shown that even a “badly fitted” mask achieves 80-90% fit effectiveness.

2. Get a Hepa-rated purifier indoors

Get one of these air purifiers. Most of these are rated for ~500 sq.ft. so make sure to get enough, or worse case, just run it in your bedroom at night.

a) Cheapest option: make your own DIY fan with a HEPA filter and a box fan. ~$20, 10minutes since you probably already have a box fan

Take a HEPA filter rated MERV 12 or higher (I recommend this one from 3M or this one, which is recommended by wirecutter)


Watch the video above for exact instructions and evidence that it works.

b) Cheaper option: slightly higher tech DIY option: $40, ~30minutes:

This blog post shows a slightly better option- putting the filters in triangle formation behind the fan in order to increase surface area and decrease the load on the fan. If you look at the comments in the youtube video above, there’s a huge discussion on whether a filter directly in front/behind the fan will cause current to increase and pose a fire hazard. It’s probably fine, but if you don’t want to risk it, use the method above.

Note if you choose this route, make sure to use the filters I linked above and not the one recommended in the blogpost article- the blogpost article was designed to filter out coarse dust from housework, not PM2.5

Side note,

My friend Thomas Talhelm from my Fulbright scholarship in China years started a whole company around cheap DIY air filters that are as effective as high-end filters, mostly marketed towards China and India:

Here’s an article from Thomas’ company detailing why  a DIY air filter will work just as well as a super expensive one:

c) Out of box option: expensive non-DIY air filter ($200, 5min setup time)

I trust the wirecutter’s recommendation of the Coway AP-1512HH.

It’s pricey, but the advantage of one of these over a DIY filter is that:

  1. It has a built-in sensor to tell you when the particle count is too high- and only starts the fan if that’s the case, saving on electricity.
  1. Update 2018-08-23: Thomas Talhelm alerted me that auto-mode in other purifiers often fails miserably, leaving the PM2.5 levels too high (faulty sensor, or too high of thresholds). I haven’t tested it on the coway, so for the purposes of this guide, I’m going to recommend you leave the filter on medium or high during heavy smoke days.
  1. The fan is designed with the load of a filter in mind- no fire risk
  2. It has a carbon filter for gas pollutants, although the it’s unclear the thickness of the carbon filter is enough to filter much out (see wirecutter article)

d) option most Seattle-ites won’t have

Most Seattle homes don’t have central HVAC, so it’s not an option, but you could try using an option like this:

e) Do I need to buy a sensor myself? As a review, the basic strategy with steps 2a-d is to rely on outdoor sensor data provided by the government via  Airvisual or Plume, then run your filters when the PM2.5 levels get above 10 μg/m3

This isn’t quite right, since indoor air usually has lower PM (although not an order of magnitude) than outdoor air even without filtering.

If you want to be accurate about when exactly to run your filters, you can buy a high end consumer grade particle filter.

I used smartairfilter’s accuracy tests to narrow down to 3 choices (Dylos DC1700, the Kaiterra Laser Egg, and the Airvisual Node). I then picked the IQAir Airvisual Pro, essentially a v2 of the now unavailable Airvisual Node (Amazon link here), since it seemed to have the best UI (Dylos is an industrial tool and looks ugly) and the backing of a large company (Laser Egg seems to be made by a startup still).

As of 10/25/2019, I’ve used mine for year+ now and really like it- it was great UI and syncs well with the Airvisual app.

I keep it in my home office and turn on my homemade filter whenever the indoor quality gets too low.

Airvisual Pro next to my Furnace-filter-strapped-to-fan homemade air filter. Nalgene bottle for reference

In my bedroom, I have a Coway running since it’s quieter, and did some tests with my Airvisual sensor which showed that the PM levels never get too high even on auto mode, so I just keep the sensor in the office, which is bigger and requires more filtration.

As of 10/25/2019, I’ve also purchased a Plume Flow portable air sensor, they seem to have a really accurate sensor:

*full history of the Airvisual Pro AFAICT. Airvisual Node was a indiegogo project from a startup 2 years ago. They became really successful and got bought by IQAir, a large Swiss company that makes air filters. They also make the app I recommended earlier

3. Eat more Broccoli, Brussel sprouts, cauliflower

This article has it all:

4. Get some eye drops for your eyes

My eyes have been stingy slightly the last few weeks (normally never do), so I called up my eye doc and asked what I could do.

In short he recommended treating with eye drops (he recommends Refresh Optive) and not to worry about long-term health effects on eyes given the short exposure to the pollution we’re experiencing in Seattle


Further resources/more reading

I’ll add more to this doc as time passes (please comment if you’re wondering about something), but if you want to do further reading, here are a few resources I recommend:

Complete medical legal disclaimer

The information contained in these topics is not intended nor implied to be a substitute for professional medical advice, it is provided for educational purposes only.

You assume full responsibility for how you choose to use this information.

Always seek the advice of your physician or other qualified healthcare provider before starting any new treatment or discontinuing an existing treatment. Talk with your healthcare provider about any questions you may have regarding a medical condition.

Nothing contained in these topics is intended to be used for medical diagnosis or treatment.