The messy science of clean air
By: Hyphae Design Laboratory
Tags: Environmental Justice, Environmental Issues, Ecology, Nature, Urbanism

How hot wax, a kitchen hand mixer, a suitcase stuffed with leaves, and dried instant noodles help people breathe healthier air.

Wax covered her lab coat. It dripped down the saran wrap protecting her laptop. One hand held a package of dried instant noodles from the neighborhood Asian grocery while the other wiped hot wax from her goggles. Old architectural designs and scrap paper captured flecks of wax flinging across the studio.

Mei Visco, Hyphae Design Laboratory Ecological Designer, thought to herself that if someone heard the small motor of our kitchen hand-mixer and walked in to see the studio draped with plastic, they might confuse it for a Dexter-style kill room.

Imagining the concerned look on their face, she considered what she’d do: point to the garbage bag filled with small leaves at her feet and say, “Don’t worry! We are measuring the surface area of leaves to see if more green space leads to positive health outcomes.”

If they still ran away, they would miss hearing how this novel and messy experiment helps produce positive health outcomes for people.

Spinning Wax (Not Just for DJs)

Mei and Daniel “Fletch” Fleischer, Head of Research at Hyphae, devised this wax-spinning process to measure leaf surface area, one step in their work to develop more specific measurement tools that support the science of understanding how variables of the built environment, like “greenness” in a neighborhood, can impact health outcomes. Many studies have developed correlative relationships between urban greenspace and both psychological and physical health outcomes but there was a need for a clinical trial.

Hyphae partnered with the Center for Healthy Air, Water & Soil at the University of Louisville’s Envirome Institute, led by renowned cardiovascular researcher Dr. Aruni Bhatnagar. With support from the Nature Conservancy, the National Institute of Environmental Health, and local donors they launched the Green Heart Project, a long-term randomized clinical trial to address the gap in research needed to establish stronger evidence for a causal relationship between green space and health outcomes. The project is measuring people’s health in a Louisville neighborhood before and after planting 8000 trees compared to a control group.

How do you evaluate the impact of “greenness?”

To establish a baseline, Hyphae Design Laboratory used normalized difference vegetation index (NDVI), a metric of greenness acquired from satellites and drones that measures wavelengths of light that likely indicate vegetation. While this metric is useful because you can collect data from across the globe, it is low resolution and not a reliable indicator to account for the myriad ecosystem benefits that one plot of greenness delivers to a person. This makes it incredibly difficult to measure before and after effects of greenness for a large-scale health study.

Based on their work on Greenheart and previous projects in Oakland, Hyphae saw a void in higher spatial and temporal resolution environmental data needed, particularly for a health study, to create a more nuanced understanding of people’s exposure to greening. Much like the complex metabolic processes tested for a pharmaceutical trial, the body’s interaction with the environment is infinitely complex and needs to be better understood and measured.

To help tackle the complex problem, Hyphae received a grant from the National Science Foundation Small Business Innovation Research (SBIR) fund to develop novel greening measurement tools and metrics.

This SBIR grant helped fund the laborious task of dipping evergreen conifer leaves in wax, then clipping the small leaves to a spinning device, that Hyphae’s team used to meticulously measure the change in weight used to determine the total amount of leaf area in one location(aka leaf density) and how it differs between different species.

Wax worked well because it coated the leaf and helped account for airflow through trees and over each leaf. Previous studies use satellite imagery to measure leaf density, but those images don’t account for aerodynamics or how air flows through a tree and not just around a tree. Mei and Fletch were thinking about leaf surface area because of a tree’s incredible ability to capture air pollutants on its leaves.

Their hypothesis: Higher leaf area means more pollutant capture, and more pollutant capture means better health outcomes. To measure a tree’s ability to do this, it is important to get a multi-dimensional measurement of leaf cover beyond a tree’s length, width, and circumference. So, Mei and Fletch left their wax dripping experiment in Oakland and flew to the Bluegrass state to measure leaf area density of an entire neighborhood.

Lite-Brite Kentucky and a Suitcase of Leaves

They logged forty hours crawling along at 12 mph in their rental car outfitted with a metal rig to hold a LiDAR scanner. LiDAR is the same technology used in self-driving cars. It uses lasers invisible to the human eye to create a 3D representation of an object. The scanner produced a 3D bunch of points called a point cloud. Their images look like high-tech Lite-Brite drawings of colorful tree-shaped constellations of points. On a grand scale, these help Hyphae measure the leaf area density of an entire neighborhood, but first they had to validate the measurements of the scan.

There is no quick and easy way to do this well. They drove to a tree-farm in Goshen, Kentucky with the LiDAR scanner and ready to stuff suitcases with leaves. Each leaf — yes, one by one — destined for a dip in hot wax at Hyphae’s Oakland studio.

Tree-Man-Extraordinaire Mr. David Listerman met the pair with 23 trees piled in the back of his trailer. Each tree was a different conifer species or cultivar that they were considering planting in the Green Heart project: junipers, arborvitaes, spruces, a pine, and a cedar. Listerman’s crew lined up the trees for them. Scanning the trees was the easy part. They drove by them at 5 different distances going 12 mph, the same speed they drove through the neighborhood. But between each scan, they would stop and partially ‘denude’ three of the trees. Cutting the leaves off of them, they removed leaves evenly from all over the tree and put the leaves in labeled freezer bags. Then, they did another set of scans, to see if the scanner picked up the change in leaf area density. After five rounds of scanning and denuding they had removed all the foliage from three of the trees. Mei and Fletch take samples of the rest of the 20 trees to test the leaf surface areas of different species.

With leaf-filled suitcases in tow, the two flew back to Oakland, rushed to the studio, and stuffed the office fridge with leaves. Even if their colleagues would have nowhere to store their Tupperware lunches and would soon have to brace for flying wax, the two returned home excited to test the wax-spinning experiment. Mei prepared the studio:

“I set up a little wax dipping chamber in a studio corner, covering things in saran wrap and hanging plastic sheets to block the spray of hot wax. Then, I carefully weighed each leaf, measuring its length and thickness, and then weighed it again after dipping it in wax. I repeated this motion hundreds of times over a few weeks at the studio. Instead of sitting at my computer working on drafting landscape plans or researching Kentucky native plants, I put on a wax-coated lab coat each morning and grabbed a bag of leaves out of the fridge.”

So, what about the dried noodles?

Mei needed to create a standard. If she could easily calculate the surface area of a metal wire or another object using the wax dipping and spinning experiment, she could extrapolate the results to help us determine the surface area of the leaves. Mei tried four gauges of metal wires — 14, 18, 20, and 24 — but wasn’t sure if wax coated the hot metal differently than the tree leaves. Next, she tried wood, thinking it might be more similar to leaves, but the wood pieces sold at the store weren’t small or flexible enough.

“So at this point, I am either hungry or experiencing a genuine Eureka moment,” said Mei. “I walked to the local Asian grocery and purchased spaghetti, vermicelli, and banh pho dried noodles. Though brittle, the noodles worked pretty well, and from there we use our data to calculate the surface areas of the different leaf species.”

She filled up a small pool with wax, fires up the hand mixer, and starts spinning leaves. Wax flew across the studio in the name of science and in the pursuit of data that might lead to healthier communities in Kentucky and hopefully other neighborhoods. Hopefully, the data from this project helps create a stronger case for society to invest in green spaces in the city environment. Trees might be more than a pleasant addition to a park, they might save lives.