Is there a mask that filters all pollution and gives 100% clean air or close to it?
Thomas here, the nerd behind Smart Air's DIY filters. I'm not an expert in air pollution, but when the air outside my window in Beijing looked like this... ...I started researching how to protect myself, and I started to nerd out with open-source tests of purifiers. Do masks work? Masks and purifiers are a technical topic, and many of the billion Chinese people around me are awakening to these same questions at the same time as me. Fortunately scientists were working on these questions before the rest of us got interested. So what'd they find? I'll break this question down into two smaller questions:1. Do masks capture the really small particles? While the population started tackling these questions for the first time, I heard some skeptical voices. Probably the most common skeptical statement I heard was: "There's no way those things get the really small particles." People are concerned about the very small particles because they can penetrate deep into our lungs and even enter the bloodstream. We're talking about particles smaller than 2.5 microns. How small is that? By comparison, a grain of sand is about 90 microns. So can masks capture particles that small? Jeremy Langrish at the University of Edinburgh tested this question by running diesel exhaust through different materials and masks and measuring how many particles penetrated the masks. Here's my super scientific rendering of his test setup: In the diagram above, I put a picture of my own particle counter, but Dr. Langrish's machine was far more sophisticated, measuring down to .007 microns--far smaller than 2.5 microns. He found that a simple cotton face cloth blocked about 30% of particles. That's not fantastic, but it's also not completely useless. But when he tested different commercially available pollution masks, the results were much better. Masks like this 3M 8812 blocked over 95% of these very small particles. 2. Do they actually work when you wear them? The second most common form of skepticism I heard is: "Sure, they work. But when you wear them, all the air just leaks in around the sides, so they're worthless!"This question is harder to test because you need to somehow test the mask while you're wearing it. But it can be done! In fact, I pestered 3M long enough for them to let me use their mask fit testing machine. Here's what it looked like while I was doing tests:The white tube draws air from inside the mask to see how many particles made it inside the mask. The blue tube tests how many particles are in the air outside the mask. Here are my results and the results of Beijing-based Dr. Richard Saint Cyr MD:Many of the simple disposable pollution masks captured over 90% of particles. Published academic studies have found similar results (1, 2). Conclusion: masks can significantly reduce the amount of particulate pollution we breathe. 3. Can we get near 100% protection? The most common type of mask is the N95, which captures 95% of particles above (and below) 0.3 microns. For me, 95% is plenty good. But there is higher protection available. The 9332 model above is an N99, which captures (you guessed it) 99% of particles. Dr. Saint Cyr and I both fit tested the 9332, and we both found it captured 99% of particles. Conclusion: N99 masks can protect us from particulate pollution at near 100%. 4. One exceptionSimple disposable N95 and N99 masks are enough to make me feel more comfortable about my health while living in Beijing. However, you'll notice that I've been talking about particulate pollution; I haven't mentioned gas pollutants like ozone and NO2. Gases are harder to capture, and I've seen fewer studies on the effectiveness of masks targeted at gases. That said, particulate pollution is what I'm more concerned about. The WHO focuses more on particulate pollution than gas pollutants. In my own experience, wearing these particulate masks has completely stopped the symptoms I used to feel while biking in Beijing--coughing, tight throat, and dizziness. However, gas pollutants are an exception to the "100% protected" criterion. More mask nerderyIf you're interested in learning more about these tests, I wrote more about mask tests in this answer: Are there any anti-pollution masks that work? I also describe a scientific study on whether masks actually have a benefit on our health in this answer: Is there a medically proven advantage to wearing a pollution mask when cycling? Breathe safe!