Plants
have long been known as the lungs of the Earth, but a new finding has found
they may also play a role in electrifying the atmosphere.
Scientists
have long-suspected an association between trees and electricity but
researchers from Queensland University of Technology (QUT) think they may have
finally discovered the link.
Rohan
Jayaratne, PhD, and Dr Xuan Ling from QUT’s International Laboratory for Air
Quality and Health (ILAQH), led by Professor Lidia Morawska, ran experiments in
six locations around Brisbane,
including the Brisbane Forest Park, Daisy Hill, and Mt Coot-tha.
They
found the positive and negative ion concentrations in the air were twice as
high in heavily wooded areas than in open grassy areas, such as parks.
Jayaratne,
who is also a member of QUT’s Institute
of Health and Biomedical
Innovation (IHBI), said that natural ions in the air were mainly created by ionization
due to two processes—radiation from the trace gas radon in air and cosmic
radiation from space.
Radon
is a byproduct of the radioactive decay of radium which is present in minute
quantities in rocks and is continually exhaled by the ground.
“Because
radium is found in rocks and radon is soluble in water, ground water is particularly
rich in radon,” he said.
“Trees
act as radon pumps, bringing the gas to the surface and releasing it to the atmosphere
through transpiration—a process where water absorbed by the root system is
evaporated into the atmosphere from leaves. This is especially prevalent for
trees with deep root systems, such as eucalypts.”
The
QUT scientists estimated that, in a eucalyptus forest, trees may account for up
to 37% of the radon in the air when transpiration rates were highest.
Jayaratne
said though there was still a lot more research which needed to be done in
relation to the role of ions, the findings, which were published in Environmental Science and Technology, have potentially
important implications for the atmosphere, climate, and human health.
“Although
there is an established link between airborne particles and human health, the
role of ions is largely unknown,” he said.
“However,
we do know that approximately one-half of the particles that we inhale during
normal breathing are retained in our respiratory system and it has been shown
that charged particles were more likely to be deposited in the lungs than
uncharged particles.
“We
do not believe that ions are dangerous—the danger comes from the pollutants. If
there are no dangerous particles in the air to attach to the ions there is no
risk of ill health.”
