Four members of the U.S. Olympic cycling team sparked outrage Tuesday when they disembarked in Beijing wearing masks covering their mouths and noses. The U.S. Olympic Committee has issued several hundred respirators to its athletes to use as they prepare to compete at the Games. Will those masks actually help?
Yes—as long as they have activated carbon in them and the athletes put them on correctly. If you're going for gold in the Madison cycling event at the Olympics, you are probably most anxious about two types of pollution: particulate matter and ozone. (Readings for other hazardous pollutants, like sulfur dioxide, nitrogen dioxide, and carbon monoxide, haven't been quite as bad in Beijing.) For competitive reasons, the USOC is not revealing the secrets behind its masks, but a team physiologist has claimed that they'll keep out "between 85 percent and 100 percent" of Beijing's pollutants.
How plausible is that claim? The simple act of holding a hankie over your nose and mouth might screen out about 20 percent of dust particles that are 3 microns in diameter. Respirators are designed to protect against the smaller particles that do more damage to your lungs. The National Institute for Occupational Safety and Health certifies respirators that are effective at filtering out at least 95 percent of all particles as small as 0.3 microns. (See, for example, this in-depth guide.) Some doctors, however, worry that NIOSH doesn't test for even smaller, "ultrafine" particles. A recent University of Cincinnati study suggested NIOSH-certified masks weren't reaching the 95 percent-protection level for ultrafine matter, but the best masks did score well enough to suggest the USOC's goals are within reach. (For a 2003 Explainer describing why surgical masks don't catch tiny viruses, click here.)
It's a bit trickier to filter out ozone gas—which has been found to inflame the lungs and restrict air flow. NIOSH recommends that workers exposed to ozone concentrations higher than 0.1 parts per million—a threshold Beijing has broken before (PDF)—should use a mask with a chemical filter. Keeping with that advice, the USOC has revealed that its masks include activated carbon, which binds to the ozone and prevents it from passing through. While there is limited evidence about the use of activated carbon in respirators, studies have confirmed that it can be effective at removing ozone in other contexts. Those studies found that quality varies significantly among different commercial filters, however. And filters meant to block ozone—like those for particulate matter—can become less effective the longer they are in use.
Even the best masks will work only if the athletes are putting them on correctly. A 2004 study (PDF) estimated that more than one-quarter of people who tried to follow the manufacturers' instructions for donning NIOSH-certified masks failed to wear them in a way that achieved the government-mandated level of protection. (Fitting a mask can be particularly tough if you have a beard or you wear glasses.) But regardless of whether they can put them on properly, don't expect to see many athletes sporting the masks on TV: Even if they get heavy use in the Olympic Village, U.S. officials say the athletes won't wear them during competition.
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Explainer thanks Ken Rundell of Marywood University and Tom Pouchot, Jeff Peterson, and Terry Thornton of the National Institute for Occupational Safety and Health.