Measuring the level of magnetism of tree leaves could be a powerful tool to monitor the air quality of streets. A new study has shown that leaves along bus routes were up to ten times more magnetic than leaves on quieter streets. The magnetism comes from tiny particles of pollution, such as iron oxides from diesel exhaust, that float through the air and either stick to the leaves, or grow right into them.

Geophysicist Bernie Housen and colleague Luigi Jovane collected several leaves from 15 trees in and around Bellingham. Five of the trees lay next to busy bus routes. Five sat on parallel but much quieter side streets. Five were in a rural area nearby. Using two measurement techniques, Housen and Jovane found that leaves along bus routes were between two and eight times more magnetic than leaves from nearby streets and between four and ten times more magnetic than rural leaves.

The inhalation of particulate matter has been linked to a number of negative health consequences, including breathing troubles and even heart problems, because tiny particles get deep into the lung tissues. For this reason the researchers say tree leaves could be a simple and effective way to measure the load of particulate matter in the air for cities planning biking routes and walking paths.

“Using trees is a nice, low-tech way to do these studies and you don’t need to use fancy particle collectors,” Housen said. “If it works, you could easily collect a lot of data from a region. You could even have kids collect leaves. That makes it a powerful tool to see variation of particulate matter on a very detailed level.”

The researchers admit that many details still need to be worked out as theirs is one of the first studies to apply the magnetic pollution measuring technique in the United States, although European researchers have been exploring the idea for a while.

The results of the study by Housen and Jovane from Western Washington University in Bellingham, WA, USA, will be presented at this month's Annual Meeting of the Geological Society of America in Portland, Oregon.

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