As noted in prior posts, significant lung damage has been
associated with the PM2.5 particulates; they are a major health hazard. Additionally, diesel is a significant source
of such particulates. Thus, researchers
considered potential options for assessing air quality in an inexpensive
researchers analyzed leaves collected at several sites along streets in
Bellingham, Washington, they found that the leaves along bus routes were as much
as 10 times more magnetic than leaves collected on quieter residential
streets. The increase in magnetism came
from iron oxide particles in emissions that were trapped on the microscopically
rough surface of the leaves.
particles smaller than 2.5 micrometers across are typically magnetic, while
those larger than 10 micrometers aren't.
Rain washes away no more than 30 percent of all the particles stuck on a
leaf, and even ultrasonic vibrations can't fully cleanse the surface. These characteristics thus make tree leaves a
good candidate for pollution monitoring.
Other pluses, according to researchers: Leaves are cheap, and they
provide information about the air near ground level where people are, not high
above the street where most air quality monitoring equipment is installed.
still must assess how the number of iron oxide particles trapped by leaves
relates to the total number of particles of different chemical classes in the
air. Because many air quality standards
are based on exposures for short periods of time, such as eight-hour or 24-hour
intervals, researchers must also assess how to estimate short-term air quality
from leaves, which accumulate particles throughout their growth.
The results of the pilot study on this strategy can be found