Every winter, when the AQI rises across northern India, masks start selling out.
Not every face covering offers meaningful protection against the fine particles in polluted air. If you are choosing a mask for pollution, here is what the evidence shows.
What are you protecting against?
One of the main concerns in winter smog is PM2.5, fine particles that can travel deep into the lungs.
A particulate respirator is designed to filter these particles. However, the protection you actually receive depends on two factors: the filter media efficiency and the facial seal. [1]
Which face coverings offer the most protection?
| Face covering | Protection from particulate pollution | Why |
|---|---|---|
| N95 / FFP2 / KN95 respirator | High, when properly fitted | Certified particulate filter media combined with a tight facial seal to minimise edge leakage. |
| Surgical mask | Limited and variable | Filter material catches some particles, but the loose fit allows polluted air to leak around the edges. |
| Cloth mask | Low and variable | No filtration standard, so performance depends on the fabric, layers and fit. The loose fit allows leakage. |
| Scarf / dupatta | Very limited | Not designed or tested as a particulate respirator, and does not seal around the face. |
This table provides practical guidance based on design and fit, not a comparative laboratory ranking.
What works?
N95, FFP2 and KN95 respirators
Technically called filtering facepiece respirators, these devices are designed to filter airborne particles and seal closely against the face.
The standards originate in different jurisdictions: N95 is a US NIOSH standard (42 CFR 84), FFP2 is European (EN 149), and KN95 is Chinese (GB 2626). [1, 7]
Under these specifications:
- N95 and KN95 require at least 95% filtration efficiency. [7]
- FFP2 requires at least 94%. [7]
- In India, the Bureau of Indian Standards certifies filtering half masks under IS 9473:2002 (which covers FFP1, FFP2 and FFP3 classes). [6]
The standard test benchmark of 0.3 micrometres refers to the most penetrating particle size (the size hardest for mechanical and electrostatic filters to capture), not an absolute cutoff. [2]
However, a printed label is not an automatic guarantee of performance:
- International standards vary in testing protocols, with some foreign classifications requiring as little as 80% filtration. [1]
- In two rounds of NIOSH testing in 2020, covering 356 assessments of non-NIOSH-approved international respirators, every unit tested filtered below 95% in 124 of them (about 35%). [8]
Fit matters
A high-grade filter is much less effective if air bypasses it through gaps:
- Straps: Many consumer KN95s use ear loops, while most N95s use two head straps. A small 2023 pilot study found that converting N95s from head straps to ear loops significantly reduced fit, because ear loops hold the respirator less tightly against the face. [9] Prefer models with two head straps where available.
- Nose seal: The bridge of the nose and the sides of the mask are common leak points. [5] Mould the metal nose clip firmly against the bridge of your nose.
- Facial hair: A beard or stubble where the respirator meets the skin can break the seal. [3]
What does not work as well?
Surgical masks
Surgical masks are loose fitting. They are designed mainly to stop contaminants from the wearer reaching the people around them, not to seal against the face and filter the air the wearer breathes in. [2]
Cloth masks and dupattas
There are no filtration standards for cloth masks, so it is very difficult to know how much they filter, and they are loose fitting. [1] A scarf or dupatta is not designed or tested as a particulate respirator and does not seal around the face.
Respirators with an exhalation valve
Valved respirators are suitable for air pollution. A respirator with an exhalation valve still protects the wearer, and the valve may make it more comfortable over longer periods of use. [10]
The trade-off is for the people around you. Exhaled air can leave through the valve unfiltered, so a valved respirator may not protect others as well as one without a valve. [1, 10] That matters if you are unwell, not for smog.
Particle filters do not remove gases
Particulate respirators only capture solid and liquid particles. They do not remove gaseous pollutants common in traffic and industrial smog, such as nitrogen dioxide (NO₂), sulphur dioxide (SO₂) or ozone (O₃). [4] Protection against gases requires a different type of respirator fitted with the appropriate cartridge or canister. [1]
Practical buying and usage rules
- Verify the standard and strap configuration: Look for certified markings (N95, FFP2 under EN 149 or IS 9473, or KN95). Prefer dual headband straps over ear loops for a better seal.
- Perform a seal check on every wear: Cup your hands over the mask and inhale sharply; the respirator should collapse slightly inward without air leaking at the edges. [4]
- Keep it on throughout exposure: Removing your mask during portions of a commute negates much of the cumulative exposure reduction.
- Do not wash or disinfect disposable respirators: Washing with soap or spraying with alcohol degrades the electret charge in the meltblown filter media, significantly reducing fine-particle capture. [11] Replace the unit when it becomes damaged, soiled or noticeably harder to breathe through. [4]
- Size appropriately: An adult respirator may not seal properly on a child's face, and NIOSH-approved respirators do not come in sizes suitable for very young children. [5]
- Check with your doctor if you have a heart or lung condition: Breathing through a tight particulate filter takes more effort.
The bottom line
A certified, well-fitted particulate respirator can reduce your PM2.5 exposure during polluted commutes.
However, a mask only protects you while you are wearing it. For your total daily exposure, indoor air quality matters too. To see how much clean airflow your home needs, use our CADR Calculator.
References
CDC/NIOSH. Respirators and Mask Types and Performance. Covers respirator types, filtration mechanics, fit, international standards, exhalation valves, and protection boundaries.
https://www.cdc.gov/niosh/ppe/php/community-respirators-masks/types-of-respirators-and-masks.htmlCDC/NIOSH. N95 Respirators and Surgical Masks. NIOSH Science Bulletin. Filtration testing at most penetrating particle sizes and mechanical distinctions from surgical masks.
https://www.cdc.gov/niosh/bulletin/2009/respirators-and-masks.htmlCDC/NIOSH. Fit Testing. Facial hair and perimeter seal integrity.
https://www.cdc.gov/niosh/ppe/respirators/fit-testing.htmlCDC/NIOSH. Filtering Facepiece Respirators. Particle filtration boundaries and gas/vapour limitations.
https://www.cdc.gov/niosh/ppe/respirators/ffr.htmlCDC/NIOSH. Community Respirators and Masks. Common leak locations and paediatric sizing considerations.
https://www.cdc.gov/niosh/ppe/php/community-respirators-masks/Bureau of Indian Standards. Product Manual for IS 9473:2002, Respiratory protective devices: Filter half masks to protect against particles. Covers FFP1, FFP2 and FFP3 classes for certification in India.
https://bis.gov.in/wp-content/uploads/2019/08/PM-9473-final.pdfRespirator standards. US: 42 CFR Part 84, Subpart K (N95). Europe: EN 149 (FFP2). China: GB 2626 (KN95). Comparative specifications tabulated in 3M Technical Bulletin: Comparison of FFP2, KN95, and N95 Filtering Facepiece Respirator Classes.
https://www.ecfr.gov/current/title-42/chapter-I/subchapter-G/part-84
https://multimedia.3m.com/mws/media/1791500O/comparison-ffp2-kn95-n95-filtering-facepiece-respirator-classes-tb.pdfCDC/NIOSH NPPTL. Filtration Efficiency Performance of Non-NIOSH-Approved International Respiratory Protective Devices. Phase One (PPE CASE P2020-0112) and Phase Two (PPE CASE P2020-0113), 2020.
https://www.cdc.gov/niosh/media/pdfs/2025/01/npptl_casereport_p2020-0112.pdf
https://www.cdc.gov/niosh/media/pdfs/2025/01/NPPTL_CaseReport_P2020-0113.pdfNiu X, Koehler RH, Yermakov M, Grinshpun SA. Assessing the Fit of N95 Filtering Facepiece Respirators Fitted with an Ear Loop Strap System: A Pilot Study. Annals of Work Exposures and Health, 2023; 67(1): 50–57.
https://doi.org/10.1093/annweh/wxac051CDC/NIOSH. Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control. NIOSH Publication No. 2021-107, 2020.
https://www.cdc.gov/niosh/publications/hcp/numbered/2021-107.htmlGrillet AM, Nemer MB, Storch S, et al. COVID-19 global pandemic planning: Performance and electret charge of N95 respirators after recommended decontamination methods. Experimental Biology and Medicine, 2021; 246(6): 740–748.
https://doi.org/10.1177/1535370220976386
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