Leaves used to measure pollution

Tree leaves may be used as a means to monitor air quality and plan biking routes and walking paths, suggests a new study by scientists at Western Washington University in Bellingham.

Leaves along bus routes were up to 10 times more magnetic than leaves on quieter streets, the study found. That 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 are trapped in them.

Geophysicist Bernie Housen and colleague Luigi Jovane collected several leaves from 15 trees in and around Bellingham in Washington. 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 10 times more magnetic than rural leaves.