Mexico City a Living Laboratory for Smog Study
Whether this city has the most polluted air in the world is a matter of debate: Indignant Mexican officials lobbied to have it stricken from the Guinness Book of World Records this year after it held the title two years running.
What’s not in question is its attraction for the hundreds of atmospheric scientists who are wrapping up a monthlong study of the reach and repercussions of Mexico City’s pollution: Where does it go? What does it become? What is its effect on climate and weather?
The answers could prove useful in cleaning up the air in other smog capitals, such as Cairo, Beijing, New Delhi and Los Angeles.
“We don’t want to say that Mexico City is polluting the whole world,” said Eric Hintsa of the National Science Foundation, one of the sponsors of the $25-million study. “But together, all the mega-cities are having an impact.”
Picking Mexico City was a no-brainer, scientists say. The air here stinks.
Like a giant San Fernando Valley, Mexico City is surrounded by mountains. This valley, though, is 7,000 feet closer to the sun -- better to cook the effluence of an estimated 9 million vehicles, oil refineries, a volcano and hundreds of thousands of leaky propane tanks hooked to stoves.
More than 20 million people are crammed into the greater Mexico City metropolitan area. By comparison, Los Angeles County is about twice as large but has only about half as many people. And everybody here seems to be burning something. Tiny particles lodge under contact lenses and deep in lungs, stoking allergies and worse. Colds last longer. And asthma sufferers really suffer.
It’s got the whiff of the familiar to chemist Jeffrey Gaffney, 56, who grew up in Riverside and is here studying how soot affects weather for the U.S. Energy Department. Mexico City, he said, is a lot like Los Angeles in the 1960s and 1970s.
Although it has improved in the last few years, Mexico City’s air quality most days still falls short of basic standards. This, despite the cleansing effect of a rainy season that runs from June to September.
Scientists already have tracked urban pollution as it moves from continent to continent -- from China to the West Coast of the United States, and from the Eastern Seaboard to Europe. This study examines regional movement.
Scientists and graduate students have been working 14-hour days to measure the giant plume of gases, dust and particles that rises out of Mexico City each day and generally drifts to the northeast, sometimes as far as the Gulf of Mexico.
Over the course of hours, the emissions mix and are altered by sunlight to create so-called secondary pollutants -- some only irritating, others carcinogenic. Using instrument readings from ground equipment, weather balloons, airplanes and NASA satellites, scientists hope to figure out how they form and how far they travel.
“I’m sure we’ll learn things we didn’t expect, answer some hypotheses and in some cases end up with more questions,” said Sasha Madronich, a chemist from the National Center for Atmospheric Research in Boulder, Colo.
Madronich and colleagues from U.S. and Mexican universities and labs have collected enough pollution data to keep them busy for years -- compiling, comparing and double-checking. They expect to announce their findings in 2007 or 2008, said Luisa Molina, an MIT chemist and one of the study’s organizers.
Getting lab-quality measurements in the field was one of daunting tasks for the project, whose unwieldy name shortens to the acronym MILAGRO -- miracle in Spanish. But the first job was moving the equipment across the border.
“We got all the stuff to the border a month early but it was still delayed four to six weeks,” said Barry Lefer, a geosciences professor at the University of Houston, who worked at a measurement site about an hour’s drive north of Mexico City.
He spoke from the roof of the Technological University of Tecamac, where he pointed out some of the exotic gear that to the layman -- and probably to customs officials -- looked sinister: sun photometers, cloud cameras, ambient particulate samplers, aerosol samplers and devices to measure solar radiation, ozone, temperature, humidity, wind and particles smaller than the width of a human hair.
Some are made by specialty manufacturers, others by hand.
Chika Minejima tinkered with her thermal decomposition laser-induced fluorescence device set up on the roof of a nearby trailer. It looked like a prop in a sci-fi thriller, but in fact measured trace amounts of a rare nitrate gas that neutralizes some pollutants overnight.
“I’ve been working on this for 3 1/2 years with another graduate student, who had been working on it three or four years before me,” said Minejima, 28, who is studying at UC Berkeley’s College of Chemistry. “I inherited it and made it more sensitive.”
It was unique, until a second one was built by scientists in Japan. “But ours is better,” said Minejima, who also built its wooden shipping container for the trip south.
In the equipment-packed trailer next door, Peter McMurray, head of mechanical engineering at the University of Minnesota, collected data for studying the transformation of airborne particles.
Clouds form when water condenses on these tiny specks. McMurray and others want to understand how pollutants create new particles over the course of a day and to be able to predict, for example, whether they will trigger more or less rain in a region. “My life’s dream is to explain these processes,” he said.
Some of the work was more old-school.
Robert Long, a graduate student in meteorology at Penn State University, was inflating an oversized weather balloon to carry an ozone monitor packed in a plastic foam six-pack holder sealed with duct tape.
“It will go up a little more than 20 miles and that will take about two hours,” he said. “It will end up over the Gulf of Mexico.”
The midday launch attracted a small group. When the balloon inflated to a diameter of about 8 feet, the plastic foam box was tied on with string. At the count of three, the balloon was released and flew skyward. And the box fell to the ground with a thud.
The scientists gathered briefly and came to a consensus: It needed stouter string.
“Let’s try it again,” Long said.
