What you can do
	Sorry, That Mask Won't Help
	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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