As wildfires were raging across the American West this summer, NPR ran a story on pollution masks people can use to protect themselves from all that air pollution.
As a non-expert nerd who has dedicated years to understanding how to live under Beijing’s particulate cloud, I was eager to see what the story got right and what the story might be missing. Here’s my rundown:
1. “When you inhale these really small particles, smaller than a few microns, they can land in your lungs and cause respiratory symptoms.” They can even pass into your bloodstream.
That’s right! Scientists are generally more concerned about the small particles. And if they’re really small, they can even enter our bloodstream.
2. For people who have underlying heart conditions or respiratory illnesses — such as asthma or chronic lung disease — exposure to wildfire smoke can be serious.
Believe it or not, the World Health Organization estimates that particulate air pollution kills a LOT more people every year through heart attacks than it does through lung problems like lung cancer or emphysema.
That means people with heart conditions should be especially careful. Studies have found more people have heart attacks on days with bad air pollution.
3. The best way for everyone to minimize the risk when skies are smoky is to stay inside.
I’ve seen many people question this logic. Our air indoors comes from outdoors, so isn’t it just the same as outdoor air?
The data says “no.” In my tests in Shanghai, Beijing, and Delhi, indoor air had 50-60% of the particulate compared to outdoor air. The US EPA found a similar number in their much more rigorous tests.
4. A standard dust mask that you can buy at the pharmacy won’t do you much good…it won’t filter out the microscopic particles that can get into your lungs.
Wrong! This is a common misconception.
Scientists have tested surgical masks against really tiny particles, and the results are surprising. Even cheap 25-cent surgical masks that researchers bought on the streets of Nepal and Beijing were 80% effective against particles down to .007 microns. Surgical masks aren’t as good at sealing around the face, but even in fit tests (1, 2, 3), surgical masks block close to 100% of particles at 1 micron and around 60% of particles at .03 microns. That’s really far from “won’t filter out.”
Of course it’s better to wear a mask designed for air pollution, like any of these masks I personally fit-tested in Beijing or these masks Smart Air tested in India. But this point about surgical masks is important because:
- Surgical masks are cheap. For some people, they’re the only affordable option.
- Surgical masks are available at many stores–pharmacies, grocery stores, and even some convenience stores.
- Sometimes surgical masks are the only option people have without waiting days for high-grade masks to be delivered.
If NPR is repeating this common misconception about surgical masks, it will discourage people from using surgical masks when they’re the only option available. When I’m in Beijing, and I don’t have a pollution mask on hand, I wear a surgical mask because it significantly reduces the amount of particulate pollution I breathe—even the really tiny particles.
5. An N95 mask can filter out 95 percent of smoke particles, but only if it’s fitted properly and dirty air doesn’t leak around the sides.
This is true by definition, but misleading. I think of how my aunt or my friend’s mom listening to this story would interpret this statement: “Bah, if I don’t get a proper fit, the mask is going to be nearly useless.”
What this statement gets wrong is that even masks that aren’t professionally fitted do an incredible job. For example, one mask study on 22 volunteers found a median fit score of 99.5%! So basically, if you take one of these masks off the shelf, chances are it’s doing a fantastic job.
But telling people that masks need to be professionally fitted will make a lot of people think, “Eh, I don’t know. That fit stuff sounded complicated. Even if I do buy a mask, it might not even work anyway. Too much hassle.”
Based on this fit test data, let’s say you’re worse than average. Let’s say you’re worse than 75% of people in the fit test. Shucks, their data says you’re breathing air that’s only 99.3% better than outdoor air.
Unfortunately that study doesn’t report the lowest score they found, but taking my fit data, Smart Air co-founder Anna’s, and Beijing-based Dr. Saint Cyr’s, the single worst datapoint for 3M masks was 84.4%. That’s still a heck of a lot better than nothing.
Bottom line: Even if you can’t get a professional fit test for your mask, it’s most likely filtering out a high percentage of particles. And you can boost that percentage by doing this simple poor man’s fit test in just one minute.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.