Every year when winter rolls around, a billion people in India are left breathing toxic, polluted air when on the streets. Be it in Delhi, Mumbai, Kolkata or Hyderabad, everyone is forced to become experts in a complicated scientific question to cope with the pollution: Do air pollution masks work?
I’ve heard doubts from smart, skeptical people all across India on this question. There’s little real data out there showing whether pollution masks work, and even less information about the brands most commonly found in India. With the help of Smart Air nerd Dhariyash, who traveled down to a pollution mask lab in Mumbai, I’ll answer those doubts!
1. “There’s no way for pollution masks to capture the really small particles.”
The skeptic case:
The most dangerous particles are the smallest particles, and levels of these are dangerously high across India. But masks are so thin! How could they possibly get those smallest particles?
The scientific pollution mask test:
Researchers from the University of Edinburgh tested different common masks by running a diesel generator (to mimic car exhaust) and piping the exhaust through different masks. They used a particle counter to see how many particles made it through the mask. This is a great benchmark for pollution in India, data shows that one of the main sources of air pollution is diesel generators (check out this report on Bangalore’s air pollution).
Here’s my super scientific rendering of the setup:
One important detail: the particle counter they used measures down to .007 microns. We’re talking about truly tiny particles here!
First, they tried a simple cotton scarf. Sometimes I see bikers in India wearing these.
Not great, 28% of particles blocked.
Next they tried a cheap surgical mask like the ones used in most of India’s hospitals:
Surprisingly good! (Fit tests generally show lower results–see below–but still a lot higher than most people’s intuition.)
Next they tried several bike masks.
Most were around 80%.
Then they tried several cheap 3M masks.
They all scored over 95%. Pretty good!
Conclusion: Masks capture even very small particles.
2. “OK, they capture the small particles, but when you wear them, all the air just leaks in the side.”
The skeptic case:
In theory, masks can catch the really small particles, but those tests aren’t on real faces! When you actually wear them, you can’t get a good enough fit, so they’re basically useless. What’s more, they’ve probably been made to fit foreign, not Indian faces!
The scientific test:
This question is tougher to answer because you have to measure the mask while you’re actually wearing it. For that, you need a US$10,000 fit-test machine. Fortunately, I begged and begged a mask company in Mumbai until they let me use their lab.
We tested a whole range of common masks you can pick up in India – including some of the most expensive, the cheapest as well as the most common. They ranged from cotton surgical masks to N90 (equivalent FFP1), to N95 (equivalent FFP2) to N99 (equivalent FFP3). Here’s the setup and the masks we tested:
And here’s how the machine works:
The blue tube is sampling air outside the mask, while the white tube is sampling air from inside the mask (more details on the methods here ).
Here are the results.
How Well Do Masks Work for the Broader Population?
It’s important to make clear: masks that fit well on Dhariyash’s face might not fit other people’s faces well. However, there is evidence from a broader population that masks fit most people well. A scientific study of 3M masks on 22 Chinese people found a median fit score of 99.5%–essentially the same as the top results from Dhariyash. Results were also nearly identical in our earlier mask tests in Beijing.
Best Mask For The Price
Best yet, the data shows effective masks don’t cost a lot of money.
Based on these results, we’re now shipping the Venus N99 masks through our online store.
Are Kids’ Pollution Masks Effective?
Two youngsters from Mumbai helped us test masks for kids. This is a crucial question for parents, because there’s far less data available on kids’ masks.
We tested a Honeywell kids’ mask with the help of Vijay (10 years old) and Pallavi (8 years old).
The Honeywell kids’ masks we tested had varying results. On Vijay, the mask captured over 90% of PM2.5. But on Pallavi, the mask captured only 50% of particles. This shows how important fit is for getting effective masks – the size and shape of your face will affect its seal.
Based on the data and the knowledge that young children are more vulnerable to air pollution, we decided to start offering these Honeywell Kid’s masks through our online store and Delhi-based office. We hope to gather more sorely needed fit-test data on a broader range of kids’ masks.
Exception: Gas Pollutants
Masks are great, but note that these are tests on particulate pollution (including PM2.5). Most commercially available masks don’t target gas pollutants like NO2 and O3, so masks are not giving 100% protection.
3. Is there a documented health benefit of wearing a mask?
This is probably the hardest question to answer. However, there are two solid studies that have randomly assigned people in Beijing to wear masks or not and measured their heart rate and blood pressure (1, 2).
While wearing masks, people had lower blood pressure and better-regulated heart rates.
We’re yet to see any tests like this done in Delhi or other cities in India, but we’re pretty certain the results would be the same.
Pollution Mask Bottom Line
Masks capture even the smallest particles—even while people are wearing them (on faces in India too!) — and they have documented health benefits. That should be enough to satisfy even the skeptics!
Paddy graduated in aeronautical engineering from Bristol University, and now runs Smart Air’s operations from Beijing. He’s an advocate for open data, free information and transparent business.