When smog descends on Beijing or other Asian cities, people rush to buy face masks.
But how effective are the masks at filtering out tiny, harmful particles of pollution?
The effectiveness varies tremendously, depending on factors like type, brand and fit. Simple, loose fitting masks do little to combat pollution, according to the United States Food and Drug Administration, whereas more advanced, government-approved respirators that bind tightly to the wearer’s face can help but may be uncomfortable. More public education and research are urgently needed about face masks, health professionals say.
“Consumers simply just don’t know which of those masks are the best,” Richard Saint Cyr, a physician in Beijing who writes a health column for the Chinese-language T Magazine once a month, said in an email. “And some indeed may be worse than helpful if people are falsely reassured and spend more time outside using a mask which doesn’t work.”
Many masks worn around Asia are simple surgical-type masks. But these are designed to prevent problems like splattering blood, not to block tiny particles, Benjamin Cowling, an associate professor of public health at the University of Hong Kong, said in an email. “It is pretty common knowledge that surgical face masks have almost no filtration efficiency against pollutants,” he said.
Surgical masks are made of polypropylene, according to Wallace Leung, the chair professor of innovative products and technologies in the mechanical engineering department at the Hong Kong Polytechnic University. His tests found that at a standard airflow velocity, basic masks captured only 20 to 25 percent of tiny particles of 50 to 500 nanometers — a size common in diesel vehicles’ exhaust. Such particles, less than 1 percent of the width of a human hair, are of particular concern because they can get buried deep in the lungs and end up in the bloodstream. The figures do not include any gap between the mask and the face that allows air to come in, further reducing efficiency
“What it means is, if you wear a face mask, you get 75 to 80 percent into the body,” Dr. Leung said. “So that’s not good.”
A better bet, experts say, are respirators that guard against at least 95 percent of small particles. Sometimes known as N95 respirators, they use thick layers of polypropylene, according to Dr. Leung, and are designed to fit tightly to the face. In the United States, such masks get tested by the National Institute for Occupational Safety and Health and must be shown to keep out at least 95 percent of all tiny airborne particles to gain approval. They are often used by industrial workers and are generally disposable.
One widely sought-after brand is 3M. The Minnesota-based company recently announced that it would invest $15 million in a Singapore plant to increase production of its N95 respirators by 70 percent.
“We definitely are seeing an increase in sales for respiratory protection” for use in China and elsewhere in Asia during hazy conditions, said Nikki McCullough, the technical manager for 3M’s personal safety division. The company said the price for its disposable respirators ranges from 30 cents to $6.70.
The respirators block particles in a number of ways as the airflow encounters layered fibers.
But respirators that guard against small particles can make it more challenging to breathe. That is especially true for people with heart or lung problems, said Tze-wai Wong, a research professor at the School of Public Health and Primary Care at the Chinese University of Hong Kong.
To improve breathability and increase filtering efficiency at the same time, Dr. Leung of Hong Kong Polytechnic University wants to create masks and respirators that use multiple layers of nanofibers. He received a United States patent last year, and “a number of companies have approached us,” he said.
Another issue is that while N95 respirators guard against small particles, they do not combat another form of traffic-related pollution: gases like nitrogen oxides or volatile organic compounds.
Some companies have created cartridges that can connect to certain respirators to block some gases. But they are expensive and cumbersome — and, Dr. Leung said, not a good choice for the public in Asia.
Dr. Leung hopes to create a system that uses sunlight and oxygen to turn nitrogen oxides and volatile organic compounds into “harmless substances, like carbon dioxide or water.” Eventually, he hopes to be able to join it to a regular, particle-filtering respirator.
More testing of existing brands of masks and respirators should be a priority, Dr. Saint Cyr said.
Aided by his blog, Dr. Saint Cyr is trying to organize independent testing for 40 brands that are commonly available in China. But he recently put the project on hold, citing the need to gain academic and scientific backing for the project.
“I feel it’s very important to warn people against masks that don’t work, as well as to tell them which work well,” Dr. Saint Cyr said, adding that research is also needed on household air-purifying machines.
Dr. Wong said that one low-tech method of combating air pollution might also be the most effective — encouraging people not to go jogging or engage in other strenuous activities during times of heavy smog. The goal, he said, is “really to try to change the behavior of people on high-pollution days.”