As large parts of north India grapple with dangerous levels of smog, two new global studies seek to settle the debate on effective ‘green’ antidotes – one concluding that potted plants do not affect indoor air quality and the other affirming that trees near factories and other pollution sources reduce outdoor air pollution. A study by the Ohio State University, published in the journal Environmental Science & Technology, on November 6, 2019, found that adding plants and trees to landscapes near factories and other pollution sources, could reduce air pollution by an average of 27%. Another study by researchers at Drexel University in the US, said claims about the ability of plants to improve the air quality were vastly overstated.
“This has been a common misconception for some time. Plants are great but they do not actually clean indoor air quickly enough, to have an effect on the air quality of your home or office environment,” Michael Waring, an associate professor in Drexel’s College of Engineering, said in a statement. Waring and one of his doctoral students, Bryan Cummings, reviewed a dozen studies, spanning 30 years of research, to draw their conclusions and published their findings in the Journal of Exposure Science and Environmental Epidemiology.
The key finding is that the natural or ventilation air exchange rates in indoor environments, like homes and offices, dilutes concentrations of volatile organic compounds – the air pollution that plants are allegedly cleaning – much faster than plants can extract them from the air. According to Waring and Cummings’s calculations, it would take between 10 and 1,000 plants per sq metre of floor space, to compete with the air cleaning capacity of a building’s air handling system or even just a couple open windows in a house.
The study by researchers from The Ohio State University, however, shows that plants may be cheaper options than technology, for cleaning the air near a number of industrial sites, roadways, power plants, commercial boilers and oil and gas drilling sites. The researchers collected public data on air pollution and vegetation on a county-by-county basis across the lower 48 US states.
In 75% of the counties analysed, it was cheaper to use plants to mitigate air pollution than it was to add technological interventions like smokestack scrubbers to the sources of pollution, the team found. “One key finding, is that we need to start looking at nature and learning from it and respecting it. There are win-win opportunities if we do – opportunities that are potentially cheaper and better, environmentally,” said Bhavik Bakshi, lead author of the study and professor at The Ohio State University.