How Good are N95 Masks For Pollution?

UPDATE: This article is old, from 2009; I have an updated article here from 2013 with a review of the best research as well as a review of three independent comparison tests of masks.

I get a lot of questions from expats, especially bikers and people walking to work, who wonder whether any type of mask is helpful. I also bike to work so I was curious as well. We’ve talked a lot about N95 masks for the flu, but how well do they work for pollution?

I previously discussed a fascinating small study done here in Beijing, with subjects walking along second ring road wearing masks. They had researched common masks and decided on the 3M company’s 8812 mask as the best for the study, which is N95 rated and also has an exhalation valve to help breathing and prevent fogging of eyeglasses. They compared this to other masks and decided that the 8812 was the best option for this test due to effectiveness, price and comfort. Here again is the graph:

The “N95” literally means that 95% of fine particles are blocked by this mask. Note that the 8812’s effectiveness in blocking particles over PM0.5 was over 96%; note also that this was far better than all 4 tested cycling masks, as well as the simple cloth masks we now see all over Beijing. Unfortunately, they did not specify which brand of cycling mask was tested. Also of note is that the simple cloth masks that are popular now in the winter (kouzhao 口罩) are minimally effective against fine particulates, only blocking 28%.

The 3M company is highly regarded as making professional-grade safety products, and they have a big line of dust respirators geared mostly for construction teams. I couldn’t find this 8812 locally, so I used Taobao and had a few boxes delivered from southern China.

My Routine

I bike to work and back, so in the mornings and evenings I will check the website to see the hourly-updated air quality at the US Embassy, only a couple hundred meters from me and therefore highly relevant. If the AQI is high (anything over 200) I will definitely use the mask on the way to and from work. Since it is at least 95% effective, that means that the most air-toxic days with AQI of 500 would bring my exposure down to 0.05% of that, or 25, which is considered safe by the WHO. So, indeed, these masks can work very well against fine particulates, the most serious pollutant. Yes, I get some looks but that’s a small price to pay for breathing better. At least in the winter it is less noticeable as most everyone is wearing some type of face mask (kouzhao) as a warmer. Today, I just bought a simple black kouzhao for 3RMB on the street and will try to wear it over the N95.

The Bottom Line

I’m very comfortable with the 8812’s effectiveness against air pollution. As for comfort, the yellow straps are fairly comfortable and the foam-lined mask is very comfortable. Plus, my eyeglasses do not fog up, a big problem with the regular N95 masks I previously used. And as for aesthetics, I do wish it were a bit snazzy and may get self-conscious in the spring and summer, but again, the health benefits far outweigh any loss of coolness.

What about other pollutants? Yes, it’s true, there are vapors, ozone, nitric oxides and others which may not be blocked by this mask. But fine particulates have the most evidence regarding long-term and short-term health risks, and are considered the most serious risk by the WHO.

What does everyone think?

I’d be very interested in having people write comments below as to what, if anything, they use, and when they decide to use it.

UPDATE: for more information, please read my N95 Masks Buyer’s Guide as well as my air pollution archives.

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37 thoughts on “How Good are N95 Masks For Pollution?”

  1. Oil-based is for use with volatile organics VOC's , i.e. paint mist/fumes, etc. you want the non-oil based masks. As much as I like riding and exercising I can't imagine doing it when the air is bad. I would suggest getting regular tests for lung capacity as a minimum, spherometers are cheap and can be done by yourself.

    1. The overall use of spirometry for lung function won’t really help people make better health decisions. Sure, it’d be interesting to see how much worse your lungs may be after a bike ride, especially an asthmatic. But with or without testing, the issue of air quality is the same. I think on the worst days, optional weekend bike rides even with a mask probably aren’t a good idea. But bike commuters don’t have that luxury…That 3M 8511 looks the same as the 8812; where did you buy it, and how much?

  2. I use the 3M 8511 mask. Comfortable and the flexible M-clip on the top allows for a close fit around the bridge of the nose. The exhalation valve is a must-have. I wear it running and walking in the morning; after about 4-6 hours of usage the filter looks brown; i cut them open each time and looking at the stuff they stop from going into your lungs is amazing!

    I'm curious how 3M has separate classifications for "non-oil based" and "oil based" pollutants — the 8511 is for non-oil pollutants.

    I presume car exhaust is an "oil based" pollutant and therefore it would be better to get one that has the oli based protection?

  3. I use the Respro Techno mask when I bike around town. If the sky looks particularly dusty I'll do a check on the Beijing API pollution index and if it's above 100 then I'll wear it when I'm walking around too.

  4. You should also ensure that the seal around the mask is intact. Hospitals use a test to ensure there are no leaks. Put your mask on and find something highly aromatic (they use vanilla) and put it near your face. If you can smell it, then you have a leak. Certain masks may not be shaped to your face or head. The problem area is often the nose piece, which does not fit snugly enough. Wearing an N95 while cycling would be uncomfortable due to the reduction of air you'll experience, but if I was in Beijing I'd use one. There are canister-style (canister is disposable) masks as well, also certified for N95. They are bulkier but may fit better.

  5. You may also be interested in totobobo mask, a transparent mask which is easier to ensure fit. I use it last time when cycling in Vietnam. I can see that it helps to block a lot of dirt from entering my lung. The best part is that the mask is reusable, and the filters are very cheap.

  6. I use constantly the Totobobo maks, with 96% filters. I think they are very good. However, I’m not a physician, so I actually would like to hear what *you* think about this kind of masks. I hope they are good — since I use only them.

  7. Yeah, is there any update on the situation? I am thinking of buying one, but it still seems very hard to get one in China. What is your opinion on the totobobo mask?

    Kind regards,

    1. I think the masks are an excellent option. As for availability, I was trying to get World Health Store and others to stock them but haven’t had any followup…

  8. Does anyone have any idea how long the industrial masks last? Obviously the totobao ones have replacable filters, but the disposable ones never really say exactly how long they are good for.

    1. I think I once read info from 3M, they said it’s ok to wear multiple times until it gets a bit dirty. But maybe not an objective source…

  9. I hope Dr. Richard and others will NOT cover their air-filters with Rmb10 cotton covers.

    By showing the air filter, one contributes to the awareness of the( local) population.
    Raising that awareness is VERY important.

    And thank you for all your info.

    Pity it is only in English, not in Chinese.
    But we understand of course: “we” have to remain behind the Great Wall (of language nowadays).

    1. Thanks for the tip. By the way, my information is also sometimes in Chinese and is shared with thousands of Chinese people on my Weibo microblog (at The awareness of air pollution, masks, the US Embassy’s monitor, PM2.5 — it has skyrocketed in the last couple months in China…

  10. Hi,

    I can only find 3M 1870 (healthcare, surgical) in my city. It’s “N95” too.
    Do you know if that’s any good against pollution? (that is, protecting the user).
    I have very few days before my trip to China so I’m inclined to buy a few of those before my trip if I still can’t find anything better.


  11. I’m wondering how many of these masks, or filters, I should buy for the seven months we’ll be remaining in Beijing. I’m having some trouble finding information on how long a single mask can be used. Some previous comments suggest only a few hours, but at almost $20/mask, I can’t afford that on my teachers’ salary.
    I’m also wondering if any one mask is better than the other. A quick look at reveals that even within the 3M 8812 category there are a number of choices.

    1. Any disposable mask can be worn for days, as the filter fabric stays the same. In fact some pollution actually filters even better but then there’s more breathing flow restrictions with more gunk. I use 3M masks at least a few days. It’s usually the smell or dirtiness that would make me switch to a new one.

      Richard Saint Cyr MD

    2. Any disposable mask can be worn for days, as the filter fabric stays the same. In fact some pollution actually filters even better but then there’s more breathing flow restrictions with more gunk. I use 3M masks at least a few days. It’s usually the smell or dirtiness that would make me switch to a new one.

      Richard Saint Cyr MD

  12. Thank you for this article. I just purchased three different brands of P100 rated masks, in preparation for a stay of several months in severely polluted Xi’an. Each has a face-seal and exhalation valve. The reason I chose these instead of an N95 mask is that N95 masks only filter particulate matter – Not vapor, gases, many hazardous chemicals, or any smoke with oil content. Since I don’t feel secure that I’m not being bombarded with chemical vapor and other hazardous smoke, I chose the highest-rated mask, and ordered a variety of styles so that I can select the one with the best fit (without a complete seal, the product will not be effective). Finally, I tried one mask which also included a carbon layer – This is supposed to filter out fumes and odors, acting mainly as a comfort and sensation filter. Anyone with more knowledge about the function of the carbon filter, or about the measurement of Chinese pollution content (what is in that filthy smog? I smell everything from coal to burning garbage and wood – and what is the best filter, based on the chemical makeup of the haze?) is encouraged to enlighten this thread 🙂 Thanks again.

  13. I would also consider the 3M R95 masks with activated charcoal filtering of organic vapors (though it does not have a valve). I found it extremely difficult to find any sort of mask while I was in Beijing recently.

    1. It shouldn’t be difficult at all, really — any 7-11, convenience store or pharmacy has N95 masks, as well as all the expat supermarkets…

  14. We (a family with two teens) are struggling between single use, “ugly” filters like 3M and cool style like Vogmask. I have an engineer education thus feeling washable filters, after a few wash, cannot really fulfill the same specifications which new filters do. So practically we should choose between a good and healthy vs cool.
    Another concern is related to conditions where masks are used. PM2.5 over 300 or 500 is not very common in US. Are they really designed for conditions in China? I feel China is more like a dusty construction site where single use filters are disposed daily after used by workers.
    Totobobo filtering areas seem very small compared to 3M. Wonder what happens to inhale resistance after a few hours AQI 300? This all seems so difficult. Any comments, please?

    1. The Vogmask “filter” isn’t anything like a coating that can we washed away, it’s intrinsic to the fabric. Feel free to email them for details. Regarding “design for China”, there’s just no data for that. I’ve blogged about the research using 3M masks around 2nd ring, and they worked great, just as they would anywhere else. So no, I’m not worried about that. Construction sites easily have super high pollution if there’s welding or dust, etc. Regarding Totobobo, their published study and real world fit tests speak for themselves, it’s objective proof…

  15. I believe the fascinating small study you mention in the second paragraph was repeated using 98 coronary heart disease patients as subjects:

    Although both experiments yielded similar conclusions, they still seem to be a very indirect way to measure effectiveness of wearing a PM 2.5 mask, and not completely convincing. How do we know, for example, that the positive influence on blood pressure and heart rate variability observed in the studies was caused by decreased inhalation of PM 2.5 particles and not larger-sized particles, or even by the psychological effects associated with wearing a mask? Is there any other evidence that these masks are really worth wearing?

    I ask because a widely-read Shanghai newspaper, Dongfang Zaobao, recently published an article in which two Chinese air pollution experts basically say masks are futile for protection against PM 2.5. One of them implies that if a person really had to breath through a filter with pores small enough to block PM 2.5, they wouldn’t be able to breath a sufficient amount of air. Here’s the link to article:

    1. I honestly don’t know what to say when other people would say that masks are futile, because it’s just inexcusably flying in the face of the actual lab tests. The N95 fit tests, mostly done by Nelson but many others, literally are pushing documented particle sizes into the mask, and measuring out the other end. It’s pure science, on someone’s face, wearing the masks and moving around in different positions for 15 minutes. These tests usually look for particles PM0.3.

      This isn’t just a public health thing, this was originally for construction sites, and it’s required by USA OSHA for many difficult work environments.

      1. Thanks for replying to my post Dr. Saint Cyr. My purpose wasn’t to cast doubt on the idea that wearing an N95 mask is a good idea in Beijing, but rather to draw attention to these statements made by Chinese pollution experts in a major newspaper. I wanted to do this because I would like to contact the said experts, as well as the newspaper, if I can find research that definitively refutes the experts’ view that wearing a mask offers no protection from air pollution. In this regard, thanks for reminding me of the fact that US OSHA requires such masks for hazardous work environments, which I think strongly suggests there is at least some benefit to them.

        You also mentioned research done by Nelson Labs. Although the company’s website looks highly professional, their study funding and profits come from device manufacturers and so one could easily accuse them of bias. They almost seem to invite such accusations on their About page: ” While we are known for exceptional quality and rigorous testing standards, we are also keenly aware of the bigger picture. It’s what we call The Science of Success™. It’s partnering with you to achieve your business goals and being fully committed to your long-term success.”

      2. The best evidence I had recently seen was what I already mentioned, those tests done right here in Beijing walking around the streets…I would assume there’s a lot of literature about construction sites or coal mines and pollution exposure reduction from N95 masks. Perhaps the NIOSH website is a good start for research. As regards Nelson, I think they’re the biggest but not the only one. So I do indeed feel they are “independent” and have valuable results.

        But it still irks me that any “expert” out there could totally disregard every NIOSH and N95 report, not to mention China’s own standards, as well as Europe’s. All of them test masks for particulate matter and all can objectively rate masks. How can anyone rationally say masks don’t work against PM2.5?

  16. I have benefitted very well from your articles and the many feedbacks form readers. Am very concern for my family and friends residing in Beijing.

    Have your heard of Pasture F550G masks which is FDA cleared, Niosh and N95 certified?

    Thought it is a very good mask in terms of comfort and fit and many can benefit from this affordable and effective disposable mask.

    1. Thanks! No, I’ve never heard of Pasture masks, but the NIOSH website has a huge list of N95 certified masks, not just 3M, which all should work just fine…

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