20,000 lightpost filters scrub Mexico City's dirty air

World's most-polluted city is installing outdoor air filters to make

The notion that technology should be able to solve the world's pollution problems is being put to the test in smog-clogged Mexico City - with 20,000 outdoor air filters.

Faced with some of the world's worst air pollution, the city is turning to homegrown technology in the form of streetlight-mounted air filters to try to bring down high levels of airborne particulates.

The first 20,000 of the stoplight-size filters are being installed in the city's central district. But the filters' developers say their "Made in Mexico" technology has global promise, since many of the world's urban centers are caught in clouds of the very kinds of suspended particulates that the filters are designed to reduce.

Backers of the plan to purify the air of this city of 10 million people make the awe-inspiring claim that the filters can reduce suspended particulates in the lowest levels of air, where humans live and breathe, by up to 60 percent. The airborne microscopic specks include metals, chemicals, fecal matter, and just plain dust that experts say constitute one of the Mexican capital's most serious health hazards.

But project detractors say the plan is at best one more misguided attempt at an easy fix for what the Washington-based World Resources Institute dubbed earlier this year the world's most polluted city.

Real solutions to the air pollution problem in general and suspended particulates in particular, critics say, lie in much tougher and unpopular public policies against deforestation and invasions of the city's green spaces. At worst, other critics add, the filtering plan could add up to a negative environmental impact, if the polluting effect of the energy used to run the filters outweighs the filters' benefits.

"We're always looking for magical solutions, for some miracle device that will solve these devastating environmental problems at no personal cost or without the necessary citizen participation," says Homero Aridjis, a prominent Mexican environmentalist.

Mexico City has seen grandiose proposals come and go for cleaning up its air: from huge fans that would blow the dirty air over surrounding mountains, to a plan to blast away one of those mountains to create a bad-air escape route. More recently some urban planners have called for a partial rebuilding of the huge lakes that once occupied the Valley of Mexico where the metropolis now sprawls. Among other benefits, the increased water coverage would reduce dry areas that generate dust.

But developers of the Respira, meaning breathe, filters say their plan is different. Instead of a macro solution to a macro problem, the developers concentrated on a micro response.

"We started with the idea that to light a city, you don't put up one gigantic spotlight, you install tens of thousands of small lights where people are," says Lino Clurana, director of Mas-O-Dos - which means "More Oxygen" - the company that developed the outdoor filters.

The filters, with different layers of materials to screen different particulates, suck in dirty air from above and "exhale" purified air toward the ground. Each filter runs off electricity supplied by the lightpost it is attached to.

The Respira project is attracting interest from neighborhoods outside the pilot project area - but also from a fair number of naysayers. "Our position is that these pie-in-the-sky solutions don't serve any purpose," says Luis Manuel Guerra, president of Mexico City's Autonomous Institute of Ecological Research. He says some Mexican scientific institutes have proven with "mathematical calculations" that it's not feasible to remove atmospheric pollutants.

"Filters only work effectively in a closed environment," says Mr. Guerra. "Then there's the problem of energy use to run the filters," which he says inevitably results in a "negative environmental balance." And even if the filters did some good, adds Mr. Guerra, there's the problem of "what you do with all those dirty filters once they're used up." But Mas-O-Dos engineers, who have the backing of the Engineering Institute at Mexico's National Autonomous University, say all those criticisms have been addressed by developing low-energy-use filters that can be fully recycled.

While not yet ready to dismiss the air-filter plan, Mr. Aridjis says it can only be viewed as a partial response, while real solutions lie elsewhere.

"If the levels of suspended particulates in the air have increased, it's because deforestation and the destruction of greenspaces in the valley have increased," he says. It's no mystery why the city is experiencing higher temperatures and dirtier air, adds Aridjis, when the natural "lungs" that filter the air and help keep down temperatures are being destroyed.

But reversing the green destruction isn't easy, since population pressures and entrenched political interests are two powerful forces behind it.

"The problem is corrupt and populist politicians who are most interested in the benefits they can reap from offering dwelling sites in these green areas," says Aridjis.

The city's environment secretary, Alejandro Encinas Rodrguez, also says the number of red-flag days for high particulate pollution has fallen from 1998's 181 to just 16 this year. At a press conference inaugurating the filters, he credited a Mexico City greenspace-recuperation program and a reduction in forest fires for the improved results.

But the encouraging numbers are nothing to be lulled by, Aridjis says. "The year's worst pollution season is still to come, when the air inversions that trap in the pollutants return with the fall," he says.

By then, most of the 20,000 filters should be showing what they can do. "We realize that the solution to our air pollution problem is complex and long term," says Mas-O-Dos director Muoz .

"In the meantime we've come up with an immediate response to help make conditions a little better."

(c) Copyright 1999. The Christian Science Publishing Society

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