for National Geographic News
Tree leaves are "magnetized" by air pollution, and the phenomenon may offer a new and inexpensive technique for quickly identifying air-pollution hot spots, scientists say.
The technique, they add, could help city officials plan healthier bike paths, walkways, and running paths.
Vehicle exhaust and other sources of air pollution spew out metallic fragments that then adhere to nearby tree leaves, said study leader Bernie Housen, a geophysicist at Western Washington University in Bellingham, Washington.
Conventional tests for measuring the amounts of these tiny particles are often expensive and time-consuming, Housen said.
"But they are very easily detected using magnetic techniques," he said.
Even "a strong magnet wouldn't [attract] the leaf, but it definitely gives you a detectable signal."
Housen, who bikes to work, was inspired to look for leaves' magnetism when he found out what diesel exhaust from passing buses might be doing to his lungs.
"Particles [from the exhaust] are deeply inhaled into our lungs," he said. "There is growing concern about the health effects of fine-particle exposure."
For example, studies suggest that particulates can cause asthma and scarring of lung tissue and, because of strain on the lungs, can even lead to heart problems.
Housen's study revealed that leaves plucked from trees along regular bus routes were up to ten times more magnetic than those on quieter streets.
While the finding wasn't exactly a surprise, it could inspire big changes among local governments.
"Up here in Whatcom County, there is only one air-quality monitoring station," Housen said, "so there isn't really any detailed picture on how variable air quality concentration is and what sorts of effects there are as to heavy traffic, et cetera."
With the new technique, "we can pinpoint places that have significantly higher particulate matter."
That information can then be used to help city planners design healthier transportation networks. (See related pictures of plans to make Paris a greener city by 2030.)
"You don't need to use fancy particle collectors," he added in a statement. "You could even have kids collect leaves."
Housen presented his findings Sunday at a meeting of the Geological Society of America, in Portland, Oregon.
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