Cleaning Big Cities' Air "Not Rocket Science," Expert Says

John Roach
for National Geographic News
October 27, 2005
Hemmed in by mountains on three sides, the basin that houses Mexico
City, Mexico, has some the dirtiest air in the world.

Pollutants spewed by power plants and tailpipes have nowhere to go. They stay within the city and compromise the health of thousands of people.

But it doesn't have to be this way, according to Mario Molina, a Nobel laureate in chemistry who is affiliated with the Massachusetts Institute of Technology in Cambridge and the University of California, San Diego.

"Technologies exist now, clean technologies that produce a lot less pollution," he said in a broadcast of the Pulse of the Planet radio program that aired yesterday.

(The National Science Foundation funds the radio program and this related National Geographic News series.)

Molina directs the Integrated Program on Urban, Regional, and Global Air Pollution, a project that seeks to resolve air pollution problems in the world's largest cities. Mexico City, Molina's hometown, is the initial focus.

The project has helped the Mexican government transition the country to unleaded gasoline and to make significant reductions in vehicle and power plant emissions.

Clean Technologies

The high altitude and ample sunlight of Mexico City create an ideal environment for pollutants to accumulate and linger, Molina said.

One major culprit, ground-level ozone, forms due to a sunlight-fueled chemical reaction between nitrogen oxides and volatile organic compounds. Commonly called smog, ground-level ozone causes a host of respiratory ailments, according the U.S. Environmental Protection Agency.

Particulate matter is the term applied to the tiny bits of dust, soot, dirt, smoke, and liquid droplets that accumulate in the air and give smog its color.

Breathing particulate matter also causes respiratory ailments. In addition, it adversely affects the environment by changing the acidity of lakes, streams, and forests.

John Walke is director of the clean-air program at the Washington, D.C.-based National Resources Defense Council, an environmental advocacy group. He says technologies exist to clean the air in the U.S. and abroad.

According to Walke, existing pollution-control technologies include:

• So-called scrubbers, which typically use chemicals or water to remove sulfur from gases produced in coal-fired power plants.

• A process known as selective catalytic reduction, which relies on the use of chemicals like ammonia to start a reaction that removes nitrogen oxides from tailpipes and smokestacks.

• Baghouses—cloth bags used to filter gas streams3which can remove particulate emissions from smokestacks.

• High-temperature incinerators that can destroy toxic pollutants.

"It's not rocket science," Walke said. "Of course there are sophisticated variations on the basic technology, but those four have more or less been in use for the last 10 to 20 years and in some cases much longer."

Use of all these technologies simultaneously is important for combating air pollution, Walke added. Each technology targets a different kind of pollution, he said—there is no "single silver bullet."

But Walke says that political will for implementing such technologies is lacking.

"Merely requiring uncontrolled [coal-fired power] plants to adopt technologies that have been around for 10 to 20 years would solve air-pollution problems in this country, at least as far as smog and soot are concerned," he said.

The utilities industry has long fought such legislation, saying that refitting existing plants with modern pollution-control technologies would be prohibitively expensive, as would building new, more efficient plants.

For example, building new oil refineries would take up to ten years and cost three billion U.S. dollars, according to the National Petrochemical and Refiners Association.

"New grassroots refineries are not necessarily the best answer for the industry," ExxonMobil chairman Lee Raymond told CNBC television. "What we really need is a streamlining of the regulations."

Technology Transfer

According to Molina, industrialized nations such as the U.S. that currently have clean-air technologies ought to work with developing countries to reduce air pollution on a global scale.

"It will be very important for the industrialized world to collaborate very closely with the developing world, so that the rich countries do not just export old, obsolete, and dirty technologies," he said.

According to Walke, the process of transferring well-developed clean-air technologies to the developing world requires the U.S. to first mandate their use at home.

"History proves that [pollution legislation is] the strongest driver for technology development in this country," he said.

"And then history has further shown that those modern technologies developed in the U.S. are adopted abroad. The rest of the world has followed our lead."

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