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The city environment department plans to plant gardens atop several city
buildings this summer as part of a U.S. Environmental Protection Agency
program studying ways to help cool cities and reduce smog. Dark-roofed buildings
-- along with miles of pavement -- absorb the suns rays, making Chicago
a huge heat island and adding as much as 4 to 6 degrees to city thermometers,
said William Abolt, acting commissioner of the city environment department.
Out of the Darkness
"The city's wearing dark clothes and it's making the city hotter,"
Abolt said. "We want to dress the city in lighter colors." Hotter
temperatures increase smog by forcing electric plants to work harder and
emit more pollution, city and EPA officials said. Pollution reacts with
heat and sunlight to create smog. That's a big issue for Chicago, which
consistently violates federal air quality standards. The rooftop gardens
could begin with City Hall and other public buildings, such as schools,
said Alexandra Holt, deputy director of the environment department. The
first gardens could be planted this year.
Trees and Lighter Pavements
The city also will plant trees and other vegetation in medians to help cool
pavement, and will consider light-colored paving surfaces, she said. Nobody
knows how many roofs would have to be resurfaced or trees planted to make
a measurable difference in heat and smog, said Virginia Gorsevski, program
analyst with the EPA's office of air and radiation. Computer modeling predicts
that widespread heat-reduction measures could easily lower a city's temperature
5 degrees, said Hashem Akbari, a researcher at Lawrence Berkeley National
Laboratory in California, which performs the modeling. But no city has ever
implemented wholesale changes to test the models accuracy. Chicago is one
of five cities participating in the EPA program and the only one promoting
rooftop gardens, Gorsevski said.
Go Away, Sunlight!
The others -- Baton Rouge, La.; Houston; Sacramento, Calif.; and Salt Lake
City -- are concentrating on roofing materials that reflect sunlight, Gorsevski
said. Holt said Chicago officials focused on gardens because roofing might
make buildings more difficult to heat during the winter. Akbari said gardens
would offer benefits similar to those of reflective roofing, but could be
more expensive. Still, researchers are eager to see Chicago's results, Gorsevski
said, adding that she knows of no U.S. city where such gardens have been
tested. Abolt said reducing emissions from vehicles and small, unregulated
businesses -- the biggest contributors to smog -- or cracking down on industrial
smokestack emissions isn't enough. Large industry contributes only about
20 percent of the pollution, he said. "We don't think traditional approaches
to dealing with smog will solve the problem," Abolt said.
Cooling City Is the Best Smog-Fighter
"He's right," Akbari said. "Based on modeling and results
of small-scale testing, cooling a city could reduce smog more than almost
every other pollution-fighting measure," Akbari said. "The chemicals
need an oven to cook in to produce smog," he said. City officials will
encourage private corporations to plant rooftop gardens. But the city must
first monitor the benefits of its own project to prove it works, he said.
The city is working with engineers and designers to plan the first gardens,
which could be simple prairie grass or more elaborate plantings, Abolt said.
He said the gardens must require little maintenance and the roofs must be
able to bear the weight of the gardens, which will not be designed for people
to use. "The point is to make it green and efficient," Abolt said.
Akbari said the potential benefits make the project worthwhile. "It
is a win, win, win case," Akbari said. "You have a better environment,
lower temperature and you save energy. "This is not rocket-science
type of business."
David Foley Holland and Foley Building Design
232 Beech Hill Road Northport, Maine USA 04849
P: (207) 338-9869 f: (207) 338-9859
E: dmfoley@acadia.net
Published by City Farmer
Canada's Office of Urban Agriculture
cityfarm@interchange.ubc.ca
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