By Chris Bowman
Bee Staff Writer
Sacramento (May 12, 2007)- Arden Middle School just happened to be in the right place at the right time. Five years ago, the local chapter of the American Lung Association enlisted atmospheric physicist Thomas Cahill to lead a volunteer study on the effects of vehicle exhaust particles in the Sacramento region.
Cahill, an international authority on the invisible but toxic floating specks, began by laying a ruler somewhat arbitrarily across an area map and drawing a line between his hometown of Davis and the foothills community of Shingle Springs, 47 miles northeast. He mounted air monitors along the transect, which happened to cross the Arden school at Watt Avenue and Arden Way.
So began a sparsely funded experiment that has produced brow-raising discoveries and low-tech pollution controls for schools and homeowners along busy roads.
The Arden school, which is sending 20 eighth-graders to Wichita, Kan., as finalists in next week’s National Science Olympiad tournament, has become a community science project in itself.
The PTA, the county roads department and even a fraternity at California State University, Sacramento, have helped plant fast-growing evergreen trees to buffer the chronic spew of harmful soot from six lanes of heavy Watt Avenue traffic flanking the school’s west side.
“When they see a problem, our parent community gets together and takes care of it,” said Peggy Piccardo, who as school principal invested some of her own sweat in the mass tree planting last fall.
The Sacramento Tree Foundation donated the young valley oaks and deodar cedars planted on the Watt Avenue side. The PTA raised $10,000 to extend the leafy pollution barriers along the campus perimeter.
When fully grown, rows of trees will form a tall green wall that should act as both a filter and a disperser of the particle pollutants, Cahill theorized. The UCD professor emeritus said he knew of no studies supporting his hypothesis when the volunteers embarked on the tree project.
A recent test of Cahill’s theory, however, suggests that the green barriers will be effective. Preliminary results announced Monday of a wind-tunnel study showed the leaves and needles of live oaks, the cedars and redwoods collecting 75 percent to 95 percent of the particles under calm or stagnant conditions.
“It’s an extremely efficient way to reduce air pollution,” Cahill told Sacramento area members of the nonprofit Breathe California, formerly the local lung association chapter.
Parents and staff mobilized a couple of years ago after Cahill gave them the surprising news that levels of particle pollution next to the school were at least as high during the day as those near Interstate 5 in downtown Sacramento, where traffic volume is four times as high. San Juan Unified School District officials upgraded the filters in the school’s ventilation system and shortened the replacement schedule to four times a year. UCD testing of the indoor air indicated that the electrostatic filters cut the pollution by at least half, Cahill said.
A growing body of studies shows that these “very fine” and “ultra-fine” particles can slip past the body’s defenses to reach the bloodstream, potentially causing heart attacks and death. Such particles are far smaller than those in wind-blown dust and typically are produced in the combustion of gasoline and diesel.
The particles, so tiny they stay aloft as an aerosol, stick to the surfaces of the trees’ leaves and needles and eventually drop to the ground in concentrations that do not harm the oaks and cedars, Cahill said. These species were selected for their resilience and fast growth rate and because they keep their foliage in the winter when concentrations of particle pollutants peak.
Once tall, the row of trees at the Arden school also should act as smokestacks, channeling the hot vehicle exhausts up and over the school’s sports fields, thereby dispersing the plume, Cahill said. The chimney effect is evident in air-monitoring studies along sections of freeways that run deep below grade or are flanked with sound walls, he said.
While the concrete structures help carry the plumes of exhaust particles aloft, they apparently are no match for trees in removing the specks from the air, according to preliminary results of a recent U.S. Environmental Protection experiment at a high-traffic highway in Raleigh, N.C.
Cahill said the EPA study, which he learned about just this week, is the first he has seen that parallels his own examination of trees and filters of ultra-fine exhaust particles from combustion of fossil fuels. “The particles seemed to hang up in the trees,” he said of the EPA study, which is still under review.
The Sacramento Bee– Health Column
The Sacramento Bee– Science Column
Sacramento Tree Foundation
Arden Middle School
American Lung Association
EPA Traffic Study