Biogeosciences News

Rooftop Gardens Make Use of the Air We Breathe Below

Growing plants near building air vents may help them grow better, while reducing the carbon emissions from the people exhaling inside.

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Trying to make a difference to mitigate climate change can seem overwhelming, but taking a first step may be as easy as breathing—at least in some buildings at Boston University (BU).

Scientists at BU found that plants grew more when rooftop gardens were placed near air vents that released carbon dioxide (CO2) exhaled by people in the building below, according to research presented in December at AGU’s Fall Meeting 2018 in Washington, D. C.

Plants in rooftop gardens can help mitigate climate change by sequestering carbon in the atmosphere, insulating buildings, and microclimate cooling. Plus they’re beautiful.

“We need to stop emitting carbon, but at this point we also need to be removing carbon,” said Sarabeth Buckley, an environmental scientist and graduate student who presented the poster. “And if we can find ways to create something beneficial to humanity and society in the process, all the better.”

Bigger Plants with Every Breath

First, the researchers assessed the classrooms, offices, and labs in a building on the BU campus using sensors that measured CO2, temperature, and relative humidity every 5 minutes for a week. Then they placed sensors at the mouths of rooftop vents to see how much of the CO2 indoors was being released. They found that air from the vents had levels of CO2 much higher than the concentration in Earth’s atmosphere. The researchers planted spinach in 32 garden boxes around four vents on the roof. Two vents released the CO2-rich air from inside the building below. The other two recycled air from the atmosphere.

Spinach rooftop garden experiment
Spinach growth in the garden boxes just before the final harvest showed that the plants grew more when exposed to vent air. Credit: Sarabeth Buckley

Overall, plants growing near vents that blew the CO2-rich air from inside the building grew more than the others. The researchers saw this effect when they weighed spinach plants collected in their first harvest after only a week and a half. Plants that were exposed to air from rooftop vents looked bigger, had more leaves, and weighed more than those that weren’t.

By the third harvest, about a month later, they noticed an even bigger difference. This seemed to indicate that the spinach plants were growing more with continuous exposure to increased carbon dioxide. Buckley also noted, however, that there was a CO2 difference as well as a temperature difference between the indoor ventilation and the control vents. Therefore, she can’t say for sure how much growth is due to one or the other. Her next study will control for the temperature variable.

More Robust Rooftop Gardens for Urban Sustainability

This study proposes one idea that may make our cities greener, literally and figuratively. “I’m enticed by the idea. It’s a great way to use something that we think of as a waste and turn it into something useful,” said Galina Churkina, a climate change scientist at Yale University who was not involved in the study.

There are limitations with such a small-scale study, like the fact that not all buildings have rooftop exhaust vents. And for this idea to be implemented on a larger scale, there needs to be a way to funnel air from indoors throughout a large rooftop garden.

However, Buckley is optimistic about future sustainable cities. She envisions buildings covered with rooftop gardens—where people can grow food to carry downstairs to their kitchens—and solar panels to provide renewable energy. “If we spread that philosophy to the rest of the city and incorporate as much green space as possible, I think cities would be more livable and sustainable,” said Buckley.

—Sofie Bates ([email protected]; @sciencesofie), Science Communication Program Graduate Student, University of California, Santa Cruz

Citation: Bates, S. (2019), Rooftop gardens make use of the air we breathe below, Eos, 100, https://doi.org/10.1029/2019EO113477. Published on 09 January 2019.
Text © 2019. The authors. CC BY-NC-ND 3.0
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