Every tree, even evergreen trees, can be used as an air quality monitor. This is the conclusion drawn by researchers at the University of Utah, who measured the magnetic properties of particulate matter on evergreen tree needles on U campus. They found that this measurement is related to overall air quality, which indicates that needle analysis (a relatively simple and low-cost process) can provide high-resolution images of air quality throughout the year.
“As long as there is a tree, there is a data point.” said Grant Rea-Downing, a PhD student in geology and geophysics. “Deploying a tree does not cost $250. We will be able to map the particle distribution with very high resolution at very low cost.”
The results are published in Earth health.
How the magnetic particles end up on the leaf
Rea-Downing and his colleagues – Associate Professor Pete Lippert and graduate students Coursey Wagner and Brendon Quirk – are both geoscientists in the Department of Geology and Geophysics, and their routine research is quite different from that of pine needles.
Lippert said: “We use the magnetism of rocks every day to find out the geographical environment of previous continents, thereby moving mountains and closing ocean basins.”
In a course called “Magnetic Earth”, Lippert introduced Rea-Downing, Wagner and Quirk to the papers of British researchers who measured the magnetism of fallen leaves to assess air quality. Lippert said: “I know that students will be surprised by what the research shows and the meaning of the discovery.”
There are many sources of particulate matter in the air, including natural wind blowing dust, brake dust, and by-products of burning solid or fossil fuels.
Lippert said: “The air is full of things, and it must come out at some point.”
When it falls from the air, some of it will of course fall on leaves and evergreen needles. The high-precision magnetometer used by Lippert in his geological work can detect iron in some of the particles. He said that iron-containing particles in the air are too small to be seen, but magnetism is an invisible method.
These documents left a deep impression on Rea-Downing, who saw the air quality in Salt Lake City contrast sharply with the normal clean air in coastal California. He can easily apply the method in Lippert’s research laboratory.
He said: “For this purpose, the kind of mountain to be climbed is actually very flat.” “We have trees outside and our seasonal air quality is poor. We have a well-equipped paleomagnetic laboratory, which means I actually Just go outside, pluck the leaves from some trees and paste them in the magnetometer.”
Lippert said: “We are not the first to explore the magnetism of pine needles to monitor air quality, but no one has tried this method to study the winter reversal in the western basin of the United States.”
With financial support from the Center for Global Change and Sustainable Development at American University, the researchers began their work.
The team selected four Austrian pine trees for sampling on U campus. Three of the trees are in a line with North Campus Drive (a frequently used campus artery), and each tree is far from the road. The fourth is near the Union Building, with inconvenient transportation. They collected pine needles twice: once in June 2017 after the summer when the air was relatively good, and once in December 2017 when the air quality was the worst in that winter.
Wagner put on a particulate filter dust mask and collected samples from December, calling them “freezing fog” because the temperature reversal across the valley caused thick yellow fog and frost on the pine needles. After returning to the laboratory, the research team used ceramic scissors to carefully cut the needle into short sections to avoid any metal contamination, and placed it in the magnetometer.
One of their experiments showed that the magnetization of the December needle is nearly three times that of the June needle. Another magnetic experiment conducted at ultra-low temperature showed that the iron-containing particles deposited during the reversal process were very small (some as small as 1/5000 the width of a human hair), and they were found to be composed of magnetite (an iron mineral) As the name suggests, it has natural magnetism. The team also checked the needles under an electron microscope and confirmed that the needles in December were obviously dirty. Other studies have linked the concentration, size and composition of particles to the health risks of air pollution.
They also studied the elements present in the particles. Lippert said that the iron content in the dust is related to the content of other elements such as titanium, vanadium and zirconium, as well as various other substances related to the combustion of brake dust or fossil fuels.
He said that other elements in the particles are related to the catalytic converter, which uses a chemical catalyst to detoxify the exhaust gas. “There is no doubt that the attention is focused on the side of the road.”
Comparing trees at different distances from the carriageway showed that the concentration of magnetic particles decreased within a distance of 50 to 150 feet. The researchers said that this may be due to the distance from the car, or it may be due to the elevation of the tree’s cross section rising a little from the hillside.
Now, the team is collaborating with atmospheric scientist Gannet Hallar and chemical engineer Kerry Kelly to discuss other issues raised by the study. They developed a new type of passive air monitor-3D printed artificial pine branches with needles to capture particles. Artificial needles and natural needles are installed side by side, which can be used as an experimental platform to better understand how and when particles settle on evergreen needles. The results can be directly compared with the particle distribution measured by the equipment in Hallar and Kelly laboratories .
Rea-Downing said: “If it rains heavily, we can collect rainwater before and after it rains to see if the signal is washed away every time it rains.” “Or the bioneedle is actually absorbing material and actually compares The synthetic needle keeps the signal longer?”
With each tree as a potential data point, pine needle analysis can provide a more comprehensive understanding of the time, causes and causes of air pollution in urban areas, thereby showing changes in air quality on a scale of tens of feet. Lippert said this analysis is simple and cheap.
Lippert said: “There are already many trees in the landscape.” “They cost very low. So this democratizes our ability to monitor air pollution throughout the valley. This is easy to export to any community. It enables us to Doing more with less, this is our hope.”
In the future, the pine needles on the old Christmas tree may become paint and food sweetener
Grant Rea-Downing et al. “Evergreen Needle Magnetization Technology” replaces particulate pollution in the urban environment. Earth health (2020). DOI: 10.1029 / 2020GH000286
Provided by the University of Utah
Citation: Evergreen needles act as an air quality monitor (September 16, 2020), retrieved from https://phys.org/news/2020-09-evergreen-needles-air-quality.html on September 16, 2020
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