Cloth masks offer poor protection against air pollution

Boston: Inexpensive cloth masks commonly used by people in India and China to reduce exposure to air pollution may not be effective and could be giving users a false sense of security, scientists have warned.

Researchers at the University of Massachusetts Amherst believe this is the first study to rigorously test disposable surgical masks and washable cloth masks, which are widely used in Asia and Southeast Asia for personal protection against
airborne particulate matter. The study showed that "wearing cloth masks reduced the exposure to some extent," but "the most commonly used cloth mask products perform poorly when compared to alternative options available on the market."

Particularly in the developing world, users should not assume that such masks convey protection, "especially if an individual makes personal choices not to avoid high concentration environments because they assume they are protected from these contaminants," said Richard Peltier from University of Massachusetts.

It was during an earlier air quality research project in Nepal that researchers were struck by how many people wore surgical or reuseable cloth masks on the street. Kathmandu has poor air quality because high polluting gasoline and diesel engines are common, as is burning tires and garbage. "We found ourselves wondering how effective these masks are. I was shocked that we couldn't find any research studies investigating them," Peltier said.

While the standard industrial hygiene mask known as the N95 is well tested, such masks are not readily available in most developing countries, and would be too expensive for most consumers. By contrast, reuseable cloth masks cost little and can be washed and worn for months.

With an experimental mannequin, researchers tested four masks: one pleated surgical type, two cloth and one cone-shaped cloth with exhalation flaps.
They tested for several variables and effectiveness in filtering out five different synthetic aerosol particle sizes plus three particle sizes of diluted whole diesel exhaust, which simulated real-world conditions. Among the cloth masks, the one with exhaust valves performed fairly well, removing 80-90 per cent of synthetic
particles and about 57 per cent of diesel exhaust.

Plain cloth masks were "only marginally beneficial" they said, in protecting people from particles smaller than 2.5 micrometres, often considered more harmful than larger particles because they can penetrate the lungs more deeply. The least expensive cloth masks removed just 39-65 per cent of standard particles of 30, 100 and 500 nanometres, and one and 2.5 micrometres.

All masks performed worse for diesel combustion particles compared to monodispersed particles, the researchers said. Peltier said this study has implications well beyond Nepal, because these masks are very common in China and India, and across much of southeast and southwest Asia. The study was published in the Journal of Exposure Science and Environmental Epidemiology.