Evergreen needles act as a monitor of air quality


Peter Leppert (left) and Grant Re-Downing examine artificial pine branches that are tested as passive air quality monitors. Photo from September 2019. Credit: Paul Gabrielson / University of Utah

Every tree, even an evergreen, can be an air quality monitor. This is the conclusion of researchers at the University of Utah who measured the magnetization of particulate matter on the needles of evergreen trees at the U Campus. This measurement, they found, related to general air quality, suggesting an analysis of needles – which is a relatively simple and low-cost process – that could provide a high-resolution, year-round picture of air quality.


“Wherever you have a tree, you have a data point,” says Grant Re-Downing, a doctoral student in geology and geophysics. “It doesn’t cost $ 250 to deploy a tree. We will be able to map Particulate Matter distributions at very high resolution at a very low cost.”

Results are published in Geohealth.

How magnetic particles end up on leaves

Re-Downing and his colleagues — Associate Professor Pete Lippart and fellow graduate students Courtney Wagoner and Brendan Quirk — are all geoscientists in the Department of Geology and Geophysics whose regular research is on a very different scale than pine needles.

“Day by day,” Lippert says, “we close mountains and close oceans using rock magnetism to explore the geography of former continents.”

In a course titled “The Magnetic Earth”, Lipter introduced re-downing, Wagner, and Quark to paper by UK researchers who measured the magnetism of deciduous leaves to assess air quality. “I knew that students must have blown their minds about what the study showed, and what the implications of the findings were,” Lippert says.

Particulate matter in the air comes from many sources, including natural windblast dust, break dust, and the byproduct of burning solid or fossil fuels.

“It’s stuff in the air,” Lippert says, “and it’s got some time to get out.”

When it falls out of the air, it, of course, falls on tree leaves and evergreen needles. Some particles contain iron, with which can be detected by a sufficiently high-precision magnetometer that Lippert uses in his geological work. Iron-bearing particulate matter in the air may be too small to see, but magnetism, he says, is a way of seeing the unseen.

The papers made an impression on the re-downing, which saw Salt Lake City’s air quality in contrast to the generally cleaner air of its Native American California. He could easily implement this method in Lippart’s research lab.

“To do this was really quite flat like a hill to climb,” he says. “We have trees, we have seasonally poor air quality and we have a fully equipped paleomagnetic lab, which means I literally just have to wander outside and pull some leaves from some trees and stick them in a magnetometer . ”

“We are not the first to detect magnetism of pine needles to monitor air quality,” Lippert says, “but no one had tried to study winter invasions in the valleys of the American West . ”

With financial support from the UK’s Global Change and Sustainability Center, the researchers went to work.

Evergreen needles act as a monitor of air quality

Scanning electron photomographograph of evergreen needle surfaces. Images of bleaching location from both during non-inverted (left) and inverted (right) are shown. Sincerely: University of Utah

Sylvan sentinel

The team selected four Austrian cedar trees at the U campus for sampling. The three trees were in a line perpendicular to North Campus Drive, a heavily used campus artery, with each tree progressively further down the road. The fourth was near the Union Building, away from traffic. He collected pine needles twice: once in June 2017 after a relatively good wind heat and again in December 2017 during some of the worst air quality of that winter.

Wagler, with his Particulate-Matter-filtering dust mask, collected December samples of what he described as “death fog from the cold”, a thick yellowish fog on the pine needles as the temperature in the valley reversed. And frost. Back at the lab, the team carefully cut the needles into short segments and inserted them into a magnetometer using ceramic scissors to avoid any metal contamination.

One of his experiments showed that the magnetism of December needles was almost three times that of June needles. Another magnetic experiment, conducted on superlo temperature, suggested that iron-bearing particles deposited during the inverse are extremely small (as small as 1/5000 the width of a human hair) and found that they were made of magnetite, An iron mineral, as its name suggests, is naturally magnetic. The team also examined the needles under an electron microscope and confirmed that there was considerable dirt in the December needles. Concentration, size, and composition of particles have all been linked to other studies for the health risks of air pollution.

He also looked at the elements present in Particulate. The amount of iron in the dust along with the amounts of other elements such as titanium, vanadium and zirconium “and are associated with brake dust or fossil fuel combustion,” Lippert says.

Other elements in the Particulate were associated with catalytic converters, he says, which use chemical catalysts to detoxify the exhaust. “And those concentrations are, to no surprise, the highest on the roadside.”

A drop in concentrations of magnetic particles was observed at distances of 50 to 150 feet compared to trees at various distances by road. This may be due to the distance from the cars, the researchers say, but possibly even to the height, as the trees move up a slight hill.

Artificial pine

Now the team has joined forces with atmospheric scientist Gannett Hallar and chemical engineer Kerry Kelly to face other questions, which have been raised in the study. He developed a new type of passive air monitoring – a 3-D printed, artificial pine branch with needles to capture particles. Artificial needles are installed with natural needles and can serve as experimental platforms to more clearly understand how and when particles settle on evergreen needles, which results in the use of instruments in Holler and Kelly’s laboratories Measured particles can be directly compared to measurements of distribution.

“If we get a strong rain, we can go and collect before and after that rain and see if this sign is getting away from the rain every time,” Re-Downing says. “Or are biological needles really absorbing the material and actually holding that signal for longer than synthetic needles?”

With every tree as a potential data point, pine needle analysis can give a more comprehensive insight into the what, when and why of air pollution in urban areas, showing differences in air quality on a scale of tens of feet. Lippert states that the analysis is straightforward and inexpensive.

“We already have a lot of trees on the landscape,” Lippert says. “They are very low cost. So it democratizes our ability to monitor air pollution in the valley. It exports easily to any community. It allows us to do more with less, or That’s our expectation. ”


Pine needles from old Christmas trees can be turned into paints and food sweeteners in the future


more information:
Grant Ri magnet Downing et al., Evergreen Needle Magnetization as a Proxy for Particle Pollution in Urban Environments, Geohealth (2020). DOI: 10.1029 / 2020GH000286

Provided by University of Utah

Quotes: Evergreen needles monitors air quality (2020, 16 September) 16 September 2020 Retrieved from https://phys.org/news/2020-09-evergreen-needles-air-quality.html.

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