The number and size of plants determines their effectiveness as botanical air filters.

Irga found that three 4-inch plants performed air-cleaning at the rate of one 8- or 9-inch plant. Wolverton indicated one plant of the larger size (a 6- to 10-inch pot) would suffice as a filter for 100 square feet in a tightly closed space.

The great number of plants required was one of the major objections raised by the EPA in arguing against the use of plants and for mechanical means of air quality control, despite the ongoing costs of the latter.

Kamal Meattle provided an exception to this EPA assessment.

Kamal Meattle purified air in a 300-person office without accessing outside air, using 1200 plants as botanical air filters.

NEW DELHI—On the roof of an office building in India’s capital, the world’s smoggiest city, Kamal Meattle has a unique tactic for cleaning the air: a greenhouse with 400 common plants, including mother-in-law’s tongue.

Meattle, the CEO of Paharpur Business Centre, has 800 other plants spread throughout the building’s lower six floors, greening each room and hallway. Their job: remove soot and other chemicals from the often charcoal-colored outdoor air.

In India, where almost no one wears filter masks on the streets as many do in China, Meattle is seen as a radical. He says he’s even been dubbed the Mad Hatter of Nehru Place, a high-tech hub that’s home to his leafy building and an adjacent lot he converted from a slum into an oasis of 2,000 trees.

He uses rainwater collected in cisterns to spray the trees so they can grow faster and absorb more pollutants. He’s urging India’s new government to require rainwater harvesting and to paint roofs, and buses, white. And he’s pushing to build one of the world’s largest energy-efficient office parks, complete with greenhouses.

Meattle hardly seems a firebrand. A soft-spoken grandfather, he’s a scion of India’s elite who attended school with Rajiv Gandhi and later earned a chemical engineering degree from the Massachusetts Institute of Technology. He sees his efforts, touted in a 2009 TED talk that’s attracted more than two million views, as common sense.

“Sustainability is good business, and energy efficiency is low-hanging fruit,” says Meattle, whose 25-year-old building was India’s first to earn the top rating (in 2010) for a retrofit from the U.S. Green Building Council. He says it uses one-fifth as much energy per square meter as the average office building in India. At least 10 percent of its energy savings is due to plants, which obviate the need to pump in ambient air.

His horticulture is also a practical nod to ancient tradition. “Why did Buddha sit under the peepul [or bodhi] tree?” he asks, adding that the sacred fig with heart-shaped leaves releases oxygen even at night, allowing those beneath a light sleep.

Good Business—and a Health Imperative

As Meattle tells it, he really had no choice but to try something new. “My doctors told me to leave” India in 1992, he says, citing his reduced lung capacity because of the city’s air pollution. He decided to stay, seeking instead to solve a society-wide problem that’s become increasingly dire. (See related story: “In Climate Talks, Spotlight Turns to India.”)

“Delhi’s unfit for living between October and March,” Meattle says, noting how often its air pollution veers into the “very unhealthy” or even “hazardous” category. The U.S. Embassy, which posts its air quality data on outdoor monitors, has issued warnings against letting kids play outside.

To see the rest of this article, click here.

See Kamal Meattle’s TED talk here.

See the next page for a Do-It-Yourself system to convert soil plants to hydroculture.