Masks to protect against China's smog not always effective, tests show
Study's lead author recommends masks marketed for workplace, which are held to a higher standard
Face masks available to consumers in China for protection against air pollution vary widely in their real-world performance, suggests a recent study.
Although a mask may filter tiny particles as advertised, face size and shape as well as movement can lead to leakage as high as 68 percent, researchers report in Occupational & Environmental Medicine.
"Even if the filtration efficiency of the mask is high, and the mask fits the person initially, the mask may not continue to give a good fit as the person goes about their daily activities — walking, talking, and more," said senior study author Miranda Loh, an exposure and environmental scientist at the Institute of Occupational Medicine in Edinburgh, Scotland.
"It is important for people to understand that not all masks are effective at reducing exposure to particles in air pollution," Loh said in an email. "And none of these masks reduced the concentration of pollution gases such as nitrogen dioxide."
Although masks sold for workplace use generally must meet rigorous standards, there are few controls on masks marketed to consumers and little information on which mask will offer the best protection, the study team writes.
Their assessment of a sampling of masks in Beijing is part of a larger project funded by the Research Councils UK, examining air pollution in the Chinese capital and its health effects.
Air pollution causes an estimated 1.6 million premature deaths in China each year, the study team notes.
At consumer outlets in Beijing, Loh and colleagues purchased nine different mask types that claimed to protect against fine particle pollution known as PM2.5, which includes soot, droplets and other particles smaller than 2.5 microns in diameter.
These tiny particles are components of vehicle exhaust and industrial emissions and can penetrate deep into the lungs, and from there, enter the bloodstream.
Researchers first tested each mask's filtration efficiency by drawing airborne diesel exhaust through a section of the material for 30 minutes and measuring the particulate matter and black carbon concentrations on both sides. They also tested four masks on 10 volunteers who were exposed to diesel exhaust in a lab while performing tasks such as talking, sitting, standing, bending over and walking in place.
In the filtration tests, the average particle and carbon penetration ranged from 0.26 per cent to 29 per cent, depending on the mask material. In the volunteers, the average leakage around mask edges ranged from 3 per cent to 68 per cent during sedentary tasks and 7 per cent to 66 per cent in active tasks. Only one mask had an average leakage below 10 per cent in both active and sedentary tests.
"If it's important for you to protect yourself or your family with masks, choose the best one you can and look for one marketed to workplaces," said lead author John Cherrie, of the Institute of Occupational Medicine.
"Don't choose the cheapest option," Cherrie said in a telephone interview. "Choose the one that's most likely to do the best job."
The researchers are now exploring whether people tend to wear face masks only on high pollution days. They also want to know if the proportion of particles removed by the mask is enough to provide health benefits, and how long people must wear a mask to see those benefits.
"Air pollution is a global problem that is important for not only Beijing, but also Boston and Barcelona. Breathing pollutants, especially particulate matter, is very harmful, causing millions of early deaths across the world," Richard Peltier of the University of Massachusetts Amherst, who wasn't involved in the study, told Reuters Health by email.
Future studies should recruit more volunteers, Peltier said, and focus on the main reasons why masks seem to fail - whether the material itself is faulty, the masks don't fit different people well, or they don't seem to work well for daily living conditions.
"Air pollution exposure is a universal burden that affects us all, and somehow we are the ones obligated to find ways to reduce our exposure with these insufficient tools," he said. "A far better solution is to prevent pollution at its source."