Mexico City's Menacing Air

By Christine Gorman.

The people of Mexico City call it nata, or scum. It is the sickly brown cloud that stubbornly hangs over the megalopolis, home to 23 million people. Composed primarily of carbon monoxide, sulfur dioxide, nitrogen dioxide and ozone, the smog has made the winter of 1991 the most toxic in Mexico City history, triggering a 16% to 20% jump in the incidence of respiratory infections, nosebleeds and emphysema. Since September, the city has enjoyed only six days in which noxious gases did not exceed danger levels. "The atmosphere has no time to recuperate," says Homero Aridjis, president of the Group of One Hundred, an environmental organization. "We have reached a chronic situation."

Last week the worsening conditions prompted Mexican President Carlos Salinas de Gortari to step up his antipollution campaign by shutting down the giant oil refinery at Azcapotzalco in northwestern Mexico City. In operation since 1933, the facility had provided 34% of the city's gasoline and 85% of its diesel fuel. But it also spewed as much as 88,000 tons of contaminants into the atmosphere each year and was responsible for up to 7% of the city's industrial air pollution.

Curbing the toxic cloud does not come cheap. The oil facility's shutdown will cost $500 million, put more than 5,000 people out of work, and require Mexico to import, at least temporarily, some refined petroleum. But even this dramatic move represents only a beginning. Three-quarters of Mexico City's air pollution comes from the capital's antiquated fleet of 15,000 smoke-belching buses, 40,000 taxis and almost 3 million automobiles. Already the government has revamped 3,500 buses with new, less polluting engines. Last week President Salinas announced a $1.3 million program to replace outmoded taxis and buses. "Let's leave a clean capital in the hands of our children," he said.

The improvements come none too soon. Since 1982, the amount of contaminants in the air has more than tripled, to 7 million tons. Because the capital lies 2,240 m (7,347 ft.) above sea level, fossil fuels do not burn efficiently, producing more ozone than normal. During the calm winter months, the mountains that encircle the city trap the polluted air close to the ground in atmospheric sandwiches known as thermal inversions.

Fortunately, inversions generally dissipate after a few hours, and there is a break of at least a few more hours before another inversion occurs. As the air grows more polluted, however, environmentalists fear the creation of a lethal inversion that remains fixed for days -- like the one that killed 20 people in the smokestack town of Donora, Pa., in 1948 or the killer fog that claimed the lives of 4,000 people in London in 1952. Even with the closure of the Azcapotzalco refinery, both Mexico's government and its industry will have to work harder at controlling pollution for years to come before the people of Mexico City can breathe easier.

With reporting by Laura Lopez/Mexico City