We hit the streets and did the math to find out what you’re exposed to—with and without a mask.

Photo: R-PUR

The Plume Labs community spends a lot of time on two wheels—biking to and from work (and school), training hard, or simply for the joy of riding. Naturally, we get a lot of cycling related questions. 

A recent study done by academics at several universities1 (including Imperial College London and Hasselt University in Belgium) found that peaks in pollution add significantly to people’s overall exposure level—and cyclists most of all 😷 

We’re not going to stop riding our bikes and neither should you. The more cyclists, the closer we get to fresh air! 

So what are your options when you’re out pushing the pedals? Masks come up in this conversation a lot so we decided to run a thought experiment. How much can a mask reduce pollution exposure while riding?

Luckily we have our most excellent Plume Labs Strava Cycling Club posting up some awesome pollution-dodging rides—making this a great starting point for our work. 

To find out what kind of pollution levels cyclists are exposed to, we pulled our data and atmospheric science teams together to look at what the Strava Club might be breathing over the course of a week.

But we didn’t stop there. 

Our users keep asking about it, so we also looked at what a pollution mask might do to change these results. We teamed up with the pollution mask experts at R-PUR to figure out just what kind of reductions in exposure our average cyclist would have gotten by wearing the new R-PUR Nano mask in Paris, New York, Los Angeles, and London.

Which city had our rider breathing the most pollution? 

City pollution level comparison (Plume AQI)

It was a close run competition between cities, but our average rider would have been exposed to the most pollution if they were in Los Angeles that week. New York City had the cleanest air breathed overall. In the middle: Paris was second worst, followed closely by London.

However, our two most polluted cities (LA and Paris) put our rider’s exposure in the Moderate level (21 – 50 of the Plume Air Quality Index (Plume AQI).  At the Moderate level you’ll be increasing the affection risk of respiratory and cardiovascular systems after a year of exposure. Our London and LA rider would have been breathing clean air (Low pollution 0 – 20) for their rides.

And with the mask?

Well, we passed on the results of our calculations to the experts at R-PUR and, based on their lab testing, they were able to show what level of filtering a good mask can provide. Across all pollutants, the concentrations are reduced to negligible amounts—into the Low (Fresh Air) category of the Plume Air Quality Index. 

How we did it ⚠️ STEM Warning ⚠️

The nutshell

Step 1: Collect biking data
Step 2: Figure out how much air a person breathes
Step 3: Calculate pollution averages for select cities
Step 4: Calculate average exposure levels for our average cyclist with/without a mask

The details

Step 1: Collect biking data

We gathered stats from the Plume Labs Cycling Club for the first week of September.

It turns out, the average rider bikes for a total 105,08km In an average of 4,93 rides a week. They spend approximately 4 hours and 57 minutes riding at an average speed 21,17km/h. 

Step 2: Figure out how much air a person breathes 

Then our team calculated how much air and average person breathes in per hour of cycling at this speed based on the 2009 study Minute ventilation of cyclists, car and bus passengers: an experimental study2 (table 3).

Now we know that bike commutes are associated with average minute ventilation of 22 and 28 L/min for men and women, respectively. Extrapolated to the 5 hour bike ride described above, we reached 6600 and 8400 liters of air breathed during the rides by men and women, respectively. Since a cubic meter of air is equal to 1000 liters, the mass of pollutants breathed by commuters can be derived by combining the average pollutant concentration with the total volume of air breathed.

So now we know how much air our average Strava Club member breathed in during their riding that week in September.

Step 3: Calculate pollution averages for select cities 

Next we went over to our data team to put these riders in 4 different cities Los Angeles, New York City, London, and Paris so we could figure out what they would be breathing if they were riding in those environments. 

Cityaverage pollution (µg/m3)

LOS ANGELES25.112.833.2
NEW YORK22.35.915.5

Step 4: Calculate average exposure levels for our average cyclist with/without a mask.

We were then able to look at our historical data for each city and calculate an average exposure for our average rider. Here’s what that looks like broken down by pollutant:

Pollution breathed WITHOUT a mask

MEN mass of pollutant breathed (µg)

LOS ANGELES165.6684.48219.12
NEW YORK147.1838.94102.3

WOMEN mass of pollutant breathed (µg)

LOS ANGELES210.84107.52278.88
NEW YORK187.3249.56130.2

R-PUR steps in

R-PUR took over with their calculations based on lab testing of their new mask the R-PUR Nano®. Because the mask is composed of 5 successive layers, it filters gases, odors, pollens, bacteria, fine particles/diesel, and toxic particles. 

The nanofiltration layers (see image above) will stop the ultrafine particles PM1 as well as particles up to a size of 50 nanometers or PM0.05 (but we’re not measuring those here).

Pollution breathed WITH a mask

MEN mass of pollutant (µg)

LOS ANGELES8.117340.042240.10956
NEW YORK7.211820.019470.05115

WOMEN mass of pollutant (µg)

LOS ANGELES10.331160.053760.13944
NEW YORK9.178680.024780.0651

For particulate matter (PM2.5 and PM10) the mask filters all traces. However, the resulting numbers are not 0 because they have to account for a certain amount of leakage along with filtration efficiency. For example, for an “elongated” face type, air filtration is 99.97% efficient. But in the case of an “oval” shaped face, filtration is at 99.90% efficiency.

To account for this range, the team at R-PUR used a filtration efficiency of 99.95% (between 99.97% and 99.90%) in their calculations.

In terms of gas filtration with the carbon filter, the range of efficiency is also calculated to account for  variations in fit.

In any case, these levels of filtration put riders exposure into the ‘Low’ or ‘Fresh Air’ category of the Plume Air Quality Index. 

But what about fit?

There are a lot of different masks on the market right now and we have tried out a ton. Fit and comfort are really difficult to quantify because everyone is so different (we see this even within our team of 30). Lab testing for filtration and fit for different face types and situations is a good place to start.


As scientists and cyclists, we know that a pollution mask is an important tool to have in your riding kit—and we also know that a good kit contains many tools. 

The clean air community has learned over the last decade, through various research projects3, that wind and weather, humidity and heat, atmospheric pressure, and many other factors create clean air pockets in urban environments. In fact, air pollution levels change up to 8X from street to street in the city, and even more from room to room indoors! With the right info, your can take steps to reduce your exposure by being strategic about picking your path. 

For the old guard, you know this already 🙂 but if you’re new to our community, this is why we created Flow—to bridge the gap between personal and collective, hardware and software, health and the environment. Its mobile companion app helps you take action to decrease your exposure and improve your environmental health. By tracking what you breathe, you can help crowdsource air pollution levels across your city—empowering others to breathe cleaner air and supporting healthier communities worldwide.


  1. https://www.sciencedirect.com/science/article/pii/S1352231019304261?via%3Dihub
  2. https://ehjournal.biomedcentral.com/articles/10.1186/1476-069X-8-48
  3. https://www.sciencedaily.com/releases/2009/10/091005102643.htm

Join the conversation! 9 Comments

  1. Hi! I would love to take part in the study in the UAE. Pollution is never talked about here and it’s often the worst in the world. I’m often found to be the only one wearing masks and local data on the surrounding islands like Saadiyat Island and Reem Island, where lots of people cycle and walk but where there is a lot of desert and construction, there are no monitors. I would be happy to supply data and contribute to the study or even just to find out the pollution levels and also see how bad is in our parking basements that have no air filtration systems.


  2. Great piece, which makes me wonder even more if cycling through my city Los Angeles is more harmful than healthy. One question this article raises re LA is that Ozone is left out of this research, whilst it’s the most dominant and harmful pollutant in LA.
    Smog (in the title of this piece) even directly refers to Ozone.

    So I’d like to understand how bad Ozone for cyclists and if a mask will help reduce inhaling those particles?

    Liked by 1 person

    • Hello Giles,

      Thank you for your message.
      You are right to ask yourself the question, ozone is a secondary pollutant, formed in the lower atmosphere from a mixture of gaseous precursors composed of nitrogen oxides and volatile organic compounds, which are necessary to produce ozone and are mainly emitted by human activities and also by vegetation.
      Concerning the gases (NOx, O3) they will be well filtered by the so-called activated carbon layer.
      For ultra-fine particles, we are talking here about particles whose size is less than 1 micron, they will be filtered by the so-called nanofiltration layers.

      You can find more information on our dedicated page: https://www.r-pur.com/pages/nos-technologies

      We hope we have answered your question.
      Have a very good day,
      The R-PUR Team


  3. I would be interested in seeing ACTUAL pollution levels on the Plume monitors when one wears a mask. You’ve taken pollution levels with no mask and applied the Mask Manufacturers’ claims of purification to the data. How do we know these are accurate? They have a biased interest in claiming the masks reduce pollution levels. I’d expect masks to filtrate out certain amounts but there needs to be a way you can measure more accurately the effectiveness of these masks by using a more scientific approach. I understand it’s not easy to put a plume monitor in betweeen your face and a mask but the above is not very conclusive.

    Liked by 1 person

    • Hello,

      First of all, thank you for your message.
      It is still difficult for the Plume team to place sensors inside the mask, perhaps one day we will succeed by linking our efforts.

      As for the figures, they are not given without a scientific study.
      Our product has been tested in an independent European analysis laboratory, attesting to its effectiveness well above the FFP3 standard. You can find the test results on our dedicated page: https://www.r-pur.com/pages/nos-technologies 

      It should be noted that today, the highest recognised standard for filtering respiratory equipment in Europe is EN149-FFP3.

      One of the tests is for filtered particles up to 0.4 micrometre in size, which is the regulatory size for the FFP3 standard, the particles tested have been:
      Paraffin Oil 
      Sodium Chloride 

      The prerequisites for EN149-FFP3 require a maximum penetration of both particles of 1%.
      Our results are around 0.15%, which is well above the norm.

      A test is also carried out on the hermeticity of the mask:
      Having optimal filtration would be useless if air were to infiltrate through holes in your mask. That’s why we have developed a memory foam technique that will perfectly match the shape of your face, combined with an ergonomic attachment system that will distribute the pressure evenly over the face.
      Our mask filters between 99.86% to 99.98% of fine particles depending on the different faces.

      Feel free to write to us directly if you have any further questions.
      Have a very good day,
      The R-PUR Team


  4. They are claiming they can filter 94% of NO2 – bull*!

    NO2 is a gas, its kinematic diameter is barely larger than that of O2 (about 30% larger). Anything that was filtering out that high a percentage of NO2, would also be suffocating you.

    Don’t repeat manufacturer claims without any critical thought! Pollution levels while cycling are still lower than the exposure of car drivers – pollution masks are a means of perpetuating the incorrect view that cycling is dangerous to try and stop people cycling and making the problem worse for everyone.

    Liked by 1 person

    • Hello James,

      Thank you for your message.
      Indeed, you are right, NO2 is a gas.

      Our filter is composed of several filtration layers.
      It is the so-called activated carbon layer that will filter out gases and odours.
      Other layers will filter out fine particles such as PM10, PM2.5 and smaller.
      You also have a water-repellent layer to filter out dust and liquids.

      If you would like more information, you can visit the dedicated section on our website: https://www.r-pur.com/pages/nos-technologies

      Do not hesitate if you have any further questions.
      Have a very good day,
      The R-PUR Team


  5. […] Wearing air quality masks used to be a bit out of the ordinary. However, one of the effects COVID-19 has had is to normalize the use of face coverings to prevent the spread of the virus. We’re watching with interest to see how this trend carries over into 2021, potentially continuing even after a vaccine has been widely distributed. Masks are a great way to reduce your exposure to air pollution. Have a look at the analysis we did on how masks can help cyclists. […]


  6. […] Mask that allows us to get out and get moving even if the air is polluted. The Nano model, that we previously presented here, was originally designed for cyclists. The R-PUR team developed the new Sport Model to be more […]



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About Plume Labs

We're here to help you understand what you breathe and take meaningful action against air pollution. https://plumelabs.com/en/


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