If you love that new-car smell, brace yourself
While that smell evokes feelings of ‘fresh’ and ‘new’, it’s the byproduct of materials like paint, carpet and plastics leeching potentially carcinogenic compounds such as benzene into the air.
These materials are found all around our built environment, from our homes to our workplaces and our vehicles. The cumulative effect is that indoor air can have two to five times the concentration of pollutants than outdoor air.
“No one believes it. Everyone thinks ‘oh, it’s polluted outside, so I’m going to go indoors’,” says Associate Professor Fraser Torpy, Director of the Plants and Environmental Quality Research Group at University of Technology Sydney (UTS).
“One of the challenges we have is people thinking that ‘new smell’ is associated with new things, therefore it’s good. But all of those materials are giving off these harmful gases, and they accumulate indoors.”
So, what can we do about it? To answer this question, UTS researchers looked to something that has a proven track record of improving air quality while also being eco-friendly: plants.
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It was a massive discovery to detect that it was the bacteria that grow on the roots in the rhizosphere that’s responsible for this.
A silent threat
Plants’ potential to oxygenate indoor spaces is well studied. Decades ago, NASA even explored the idea of using plants to provide air for astronauts on the International Space Station. They found oxygen levels increased, but they also made a surprise discovery: while the plants were expelling something helpful, they were also removing something harmful.
“What they found was the air inside the Space Station … all these toxins were gone, and they thought it was the plants that actually removed the toxins,” Torpy says.
“So we thought, ‘well, that could work in our indoor spaces as well’, so we started looking at it from that angle. Twenty-something years since then, we’ve tested every type of air pollutant, every type of plant we can.”
In a world-first, this research looks specifically at pollutants found in petrol vapours. While not immediately harmful, the effects of inhaling these compounds over time can contribute to the development of cancer and other chronic illnesses.
“The analogy I like to use is brushing your teeth: you’re not going to see overnight changes from brushing just once, but you will from continuously brushing your teeth,” says Dr Peter Irga, Senior Lecturer in the School of Civil and Environmental Engineering at UTS.
“It’s that consistent and persistent exposure to whatever the toxin is that has a cumulative effect.”
Petrol vapours, surprisingly, are found in high concentrations in indoor spaces because of the popularity of underground car parks and attached garages.
“When studies have gone out and measured the effects, they’ve found that the biggest source of highly dangerous carcinogens in non-smoking individuals – it’s the bloody car garage,” Torpy says.
“When someone starts up their engine, they’re creating volatile compounds from petrol vapours and that’s going straight into the buildings.”
But it’s not just petrol fumes from vehicles that are the culprit. Air pollutants can be generated from carpet, lacquer and paint, plastics and other synthetic materials.
“We can’t fix building design – we do plants and air quality”, Torpy says, “so the experiment became obvious.”
Small but mighty
Irga and Torpy are both leaders in the growing field of using nature-based systems to address air pollution, the urban heat island effect, biodiversity and a host of other challenges. Between the two of them, they have more than four decades’ worth of experience in green infrastructure, as well as numerous accolades including a Tall Poppy Science Award for Irga.
Torpy and Irga teamed up more than a decade ago to research how green infrastructure can be about function as much as form. Irga has an engineering background, while Torpy has a background in biotechnology and microbial ecology. Their combined expertise alongside colleagues in the UTS Faculty of Design, Architecture and Building as well as the Institute for Sustainable Futures makes for a formidable force. This research collaboration was further strengthened through a partnership with Ambius, a leader in indoor plantscaping solutions.
This mix of expertise and experience was particularly useful in devising experiments to test plants for their air-filtering abilities, as well as translating the results into practical solutions.
There are roughly 120 different chemicals within petrol, so first the team needed to work out the rates at which each chemical is filtered out. The team placed Ambius green walls comprising different plant species within a sealed chamber and subjected them to petrol fumes. Various configurations, types of air flow and filters were used to test different scenarios. Gas chromatography and photoionization detectors determined the chemical composition of the air within a set timeframe after exposure. What they found astonished them.
Results showed the plants were able to remove nearly all of the most toxic petrol-related compounds from the air within eight hours. Even more astounding, the plants preferentially degraded and removed the most dangerous chemicals first, including benzene, formaldehyde and alkanes (sometimes called paraffins).
Contrary to what you might think, the main method of pollutant removal is not through the leaves. It’s actually bacteria housed in the plant’s roots – called the rhizosphere – that do the dirty work.
The pollutant removal is not characteristic of specific bacteria, either.
“There are billions of bacteria in soil and millions of species, so it’s this whole community that’s operating here,” Irga says.
“We’re currently running experiments to see how that community responds to pollutants and how we can encourage those specific bacteria so that we can increase the rate in which plants remove air pollutants.”
24%
of toxins are removed by plants within 8 hours of exposure
We bring together every discipline, and that’s so critical in today’s day and age. That breadth of transdisciplinary expertise is really important and really useful. There’s always someone who can answer any question.
Green is good
The impact of this is that green walls aren’t just decorative, but a promising technology. However, a challenge remains: how to set up these living filtration systems inside actual work and living spaces.
According to the researchers, you need more than 200 plants to filter the air inside a space. Most office spaces or homes are lucky to accommodate a handful given available floor space.
“That’s our greatest barrier: the plausibility factor,” says Torpy.
With horizontal space at a premium, the only viable solution is to build vertically.
Working with industry partner Ambius is allowing the team to take lessons learnt from this research and trial different methods for constructing active green walls in a real-world context.
The team has been experimenting with green walls placed near air vents and HVAC systems to draw air through the plant substrates. This exposes the bacteria in the rhizosphere to toxins in the air and provides ample opportunity to degrade and filter them.
Researchers are also exploring different substrate combinations to ensure that plants placed near air vents aren’t unintentionally introducing different harmful particles into the air, such as plant spores.
“We’re not saying strap a fan to any green wall,” Irga says.
“We’ve done substantial R&D on substrate development to have a system more or less optimised for air pollutant removal.”
Another option they’re exploring is to place plants as part of green roofs, again near air intake units to ‘pre-filter’ the air before it’s drawn into the building. For a fully integrated green solution, the team even recommends co-locating plants with rooftop solar. In this scenario, the plants do double duty: they help filter out toxins in the air while keeping the solar panels cool enough to operate at their most efficient temperature range.
Although there is still work to be done, Torpy and Irga envision a future where indoor and outdoor spaces are completely bathed in green.
“Every time you envision a future city, what does it look like? It looks like a utopia that’s covered in plants, right?,” Irga says.
“It always has. And even if that’s idyllic, even if that’s a vision, we’re working towards that vision.”
22%
average amount of their time a person spends indoors
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