Magnetic leaves could see trees used as low-cost air quality monitors
Advances in technology have allowed for some high-tech ways to monitor air quality, from satellites that orbit the Earth to art installations that light up when pollutants are low. Scientists at the University of Utah have come up with a relatively low-tech solution, demonstrating how the buildup of magnetic particles on tree leaves can be used to gauge the quality of the surrounding air.
The research was actually carried out by geologists who normally investigate the makeup of former continents by studying the magnetism of rocks. As part of this, the team looked at previous research that demonstrated how leaves can trap magnetic particles released from vehicle exhaust and fossil fuel emissions, and could therefore be used to track airborne pollutants through urban environments.
These particles are often too small to see with the human eye, but some contain iron in high enough concentrations to be detected with the magnetometers the geologists use in their typical line of work. So the researchers set out investigate the potential for tree leaves to serve as air quality monitoring stations in their local area.
This involved collecting pine needles from four evergreen trees on campus, three of which were near a heavily used road but each being located farther from the traffic than the last. The fourth was situated well away from the traffic. The scientists gathered samples at two points, once after a 2017 summer of relatively good air quality and once in the midst of a winter, when the air quality was at its worst for the season.
Using magnetometers and electron microscopes, the team found that the magnetization of the needles collected in winter was around three times higher than those collected in the summer. These winter needles were found to be significantly dirtier, with the scientists uncovering evidence of other elements in the particles such as titanium, vanadium and zirconium, and others associated with brake dust, fossil fuel combustion and exhaust fumes.
The team found that the concentration of magnetic particles was lower in samples collected farther from the road, which they say may be due to the distance from vehicle traffic but could also be due to elevation, with the line of trees following an incline.
To take this concept further, the researchers have developed an artificial pine branch, 3D printed with needles to gather its own particulates. The scientists will use these experimental platforms to gain a better understanding of how the magnetic particles accumulate on these needles, and explore the effects of other factors, such as rain.
“If we get a strong rain we can go and collect before and after that rain and see if this signal is just being washed away every time you have a rain event,” says study author Grant Rea-Downing. “Or are the biological needles actually absorbing material and actually holding onto that signal for longer than the synthetic needles?”
All going well, the team sees great potential in this approach as a way of offering precise data on air quality in urban areas, possibly revealing variations in areas only tens of feet apart. Working in its favor is the fact that the infrastructure is already in place, offering a cheap and simple way to implement the method on a large scale.
“Wherever you have a tree you have a data point,” says Rea-Downing. “A tree doesn’t cost $250 to deploy. We’ll be able to map particulate matter distributions at a very high resolution for very little cost.”
The research was published in the journal GeoHealth.
Source: University of Utah