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Myth of Air
Filters
By Bryan Walsh
Posted Monday, December 13, 2004; 20:00 HKT
Air is the one commodity that everyone on Earth has to share—it's
tough to find bottled oxygen—so we can only protect ourselves from
pollution through collective effort. But that hasn't stopped the
circulation of half-truths and outright errors about how to shield
yourself. A guide to what you need to know:
MYTH: A surgical mask can screen out air pollution.
FACT: Absolutely untrue. Surgical masks can't filter out the
relatively tiny particles and gases like nitrogen dioxide that cause
the most damage to your body. Gas masks with fine air filters can
offer some protection, but the filters need to be changed often and
the masks are uncomfortable, especially in warm weather.
MYTH: You can escape air pollution by living near the top of tall
apartment towers.
FACT: Not really. Although it's good to be away from intense
roadside pollution, bad air rises well above the apartment level.
Andrew Cheng, a physicist with Hong Kong's City University, has used
laser measurements to show that pollution levels in Hong Kong often
remain steady at heights of up to 700 m. The best way to avoid air
pollution is to live in an outlying area with low traffic density
and away from power plants. Still, if you work in the city center,
you'll get a hefty dose of pollution on your long commute.
MYTH: A filter can keep air pollution out of your home.
FACT: There's little data to show conclusively that air filters
are worth the money. Most filters fail to screen the fine particles
that cause the most damage. Dr. Seamus Ryan, chair of family
medicine at Beijing United Family Hospital, suggests that sensitive
children in dry climates can benefit from sleeping in a room with a
humidifier and a High Efficiency Particulate Air filter, which
screens particles as small as 0.3 microns and costs up to $500. "At
least that way they're getting better air for 10 hours a night," he
says. Of course, they'll still be exposed to pollutants during the
day in school or outside.
MYTH: Air pollution causes asthma.
FACT: There are no concrete studies that directly link asthma to
air pollution. The asthma rate in heavily polluted Beijing is
actually lower than the rate in Hong Kong, which is itself lower
than in many cleaner cities. But asthmatics who move to polluted
cities do find themselves at greater risk. "There's no question that
once you have asthma, you're more vulnerable to air pollution," says
Dr. Anthony Hedley of the University of Hong Kong.
MYTH: Closing your windows and turning on the air conditioner
will keep out pollution.
FACT: Unless your apartment comes equipped with an air lock and
an independent oxygen supply, this won't help much. Indoor air
pollution from cooking or aerosol fumes can quickly make an
unventilated apartment more toxic than the pollution outside. It's
best to try to keep a well-ventilated indoor environment, although
that can be problematic if you live near heavy traffic or other
pollution sources. If that's the case, there's not much you can do
beyond holding your breath.
With reporting by Adam Shemper/Hong Kong
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