Leafing the Air Clean

When students at Stuyvesant High School in Manhattan returned to their classrooms four blocks from ground zero on October 9, they found a new next-door neighbor--a loading dock for debris from the disaster site--and dusty, irritating indoor air. Many complained of sore throats, headaches, fatigue and breathing problems. Although the Parent Association sought improvements to the school's air-filtration system, this would take time. But in a week, after a student's suggestion that green plants might help, and some phone calls by Annette Arroyo, assistant to the principal, 1,000 free plants had arrived, donated by members of the Florida Nurserymen and Growers Association. The growers based their choices on a study showing that common houseplants have the ability to reduce carbon dioxide and vapors from toxic, irritating volatile organic compounds (VOCs), traces of which were found in a November test of the school's indoor air.

The research, conducted by Bill Wolverton, Ph.D., for the National Aeronautics and Space Administration in the 1970s, measured how well a single plant works to clean the air in a sealed chamber. Extrapolating from these results, Dr. Wolverton says that three plants per 100 square feet in a home or office will improve air quality (the growers sent at least three plants for each of Stuyvesant's 110 rooms). But to maximize results from any filtration system, organic or mechanical, "you need a tightly sealed building that keeps polluted outdoor air from coming in," he says.

To enhance green screening, Dr. Wolverton has developed a filter system that can increase a plant's effectiveness by 200 to 300%. It includes a medium of activated carbon and clay in water, with a fan that pulls the air through and a UV light that kills bacteria, viruses and molds. Even without these embellishments, however, "having plants in your immediate breathing space will help," he says. (If you have allergies, Dr. Wolverton does advise putting a layer of aquarium gravel on the surface of the soil to reduce mold growth.)

The Stuyvesant classroom greenery lacks Dr. Wolverton's filter system. And, in any case, plants can't absorb the particulates (such as asbestos, fiberglass, lead and soot) that are of main concern here. But, although environmental testing may not prove it in this case, there's little doubt that the plants have helped to clear the air in more ways than one. "Everyone loves the plants. They give us a nice boost," Ms. Arroyo says. "Two days after the arrival of the plants, the pain in my throat went away, and the intensity of the headaches subsided significantly," Leah Rabinowitz, a Stuyvesant student, writes in her winning essay for a contest sponsored by Plants at Work, a nonprofit group. And runner-up Lisa Cao reflects on a classroom peace lily: "The name of the plant alone brings a message of hope, and looking at its cheerful white flowers is uplifting for me."

Inspired by Stuyvesant, the plants-in-the-classroom program, still supported by Florida growers' donations, has expanded to other area schools.