As the evening thunder turned to nocturnal rainfall last week, residents here seemed to breathe a collective sigh of relief — savoring both the cooling and cleansing effects of long-awaited spring showers.

For more than a month, Mexico’s capital had been in the grip of a prolonged stretch of unseasonable heat, sparse winds — and some of the worst air pollution the city has seen in more than a decade.

The photochemical cloud hovering over the city of 20 million-plus residents had schoolchildren eating their lunches indoors and forced authorities to implement strict new traffic reductions that further strained an overtaxed public transport network.

“Fortunately, it finally rained and the heat has gone down a bit,” Rosaura Garcia, a 42-year-old dentist, said last week after the first showers dispersed the stagnant and stultified air. “The previous days were a nightmare, with so much heat, the contamination and a collapsed public transport.”


See the most-read stories this hour >>

Mexico City has long been identified with some of the planet’s vilest air pollution, a noxious, sun-irradiated fusion of vehicular and industrial fumes trapped in the high-altitude valley where the sprawling urban expanse sits. Thermal inversions linked to meteorological conditions in the dry months have threatened residents’ health and dampened moods.

In the 1980s, the air was so famously foul that stricken birds were reported to have tumbled from the sky in mid-flight, as the toxic brew contributed to elevated mortality among humans. The United Nations labeled Mexico City the world’s most polluted city in 1992.

But all that had changed — or so it appeared. The narrative after the late 1990s became how tough government action — including strict controls on emissions and limits on vehicular traffic — produced a stunning turnaround. The city achieved substantially reduced levels of lead and other toxic components in the air, and a rise in the number of radiant days when strollers downtown could catch a glimpse of the majestic, snow-capped volcanoes of Popocatepetl and Iztaccihuatl.


I arrive home every day with a headache. We’ve suffered from terrible heat on the one hand, and a saturated public transport system. Carla Medina, 35

The international air pollution focus gradually shifted to such unfortunate capitals as Beijing, New Delhi and Tehran. Many experts held up Mexico City as a success story, a model for other developing nations coping with toxic atmospheres.

But the capital’s upbeat eco-storyline has stalled. In mid-March, authorities declared the first air pollution warning since 2005 and pronounced an environmental emergency. The pressing culprit was ozone, a key component of smog, but officials also cited high readings of other toxic substances.

The crisis culminated this month, when authorities took the extreme step of banning about 40% of the more 5 million vehicles that daily transit the city and suburbs, forcing many residents onto public transit and creating tortuous commutes. People spoke of trips to work that normally took an hour mutating into two- and even three-hour odysseys.


“I arrive home every day with a headache,” complained Carla Medina, 35, a secretary in the capital, speaking before last week’s rains afforded some respite. “We’ve suffered from terrible heat on the one hand, and a saturated public transport system.... The lines are so long to get into a bus, and when you finally get in it’s completely packed; the heat and the odors are terrible.”

Many young people had never confronted full-blast Mexico City smog. Some had consigned the experience to a distant past.

Then there are those who see an otherworldly force in the tribulations of a city that radiates out from what was once the capital of the storied Aztec empire.

“I believe that Tlaloc is very vexed with los capitalinos,” offered Javier Diaz, 21, a student, pointing the finger at the temperamental Aztec rain deity. “This is a punishment for not keeping the city clean, for keeping it so contaminated, and above all for having such terrible politicians.”


Environmentalists and other critics complain that after the early improvements in pollution, authorities failed to follow up decisively on further regulation of vehicular and industrial emissions, improvements to public transport and controls on chaotic urban expansion.

This year’s weather conditions served to expose the shortcomings.

In a recent report, the National Autonomous University of Mexico’s Center for Sciences of the Atmosphere cited “the decisions affecting the disorderly growth of the city, the lack of investment and planning in public transport, among other factors.”

Indeed, as columnist Leo Zuckermann noted in Excelsior newspaper, car sales rise steadily in part because residents seek to “emancipate themselves from the buses and trains where they travel like canned sardines — and, on top of everything else, lack security.”


Mexican President Enrique Peña Nieto conceded that things had gone amiss.

“Lamentably, the quality of air in the metropolitan zone, particularly in the Valley of Mexico, has been deteriorating notably in recent months [and] in recent years,” he said at a public forum in March, referring to the vast area that includes Mexico City and environs.

The president called on federal, state and municipal authorities to adopt bold new measures. There have been new official vows to tighten emissions controls and get 1.7 million more pollution-belching vehicles off the streets, in part by detecting cheaters who manage to beat the system.

In a city where official pronouncements are regularly viewed with skepticism, however, many are dubious. They point out that the government so far has failed to impose strict controls, for example, on emissions-heavy mini-buses, or take decisive steps to ease the city’s constant state of traffic gridlock.


“To reduce the numbers of cars circulating is not the solution,” said Marisela Ortega, 21, a psychology student. “On the worst days [in May] almost half the cars were not circulating, and there was no difference in the air. Our eyes and noses still burned. The authorities need to have better strategies.”

patrick.mcdonnell@latimes.com

Cecilia Sanchez in the Mexico City bureau contributed to this report.

ALSO


U.S. intelligence warns of Venezuela collapse

In post-impeachment Brazil, the new conservative Cabinet is 100% white men

Obama administration plans new raids that would deport Central American children