Air Pollution

In 1992, the United Nations described Mexico City’s air as the most polluted on the planet. Six years later, that air earned Mexico the reputation of “the most dangerous city in the world for children” — a reputation Mexico has been working hard to improve. But despite more than a decade of stringent pollution control measures, a haze hangs over the city most days, obscuring the surrounding snow-capped mountains and endangering the health of its inhabitants.

Many factors have contributed to this situation: industrial growth, a population boom (from three million in 1950 to some 20 million today), and the proliferation of vehicles. More than 3.5 million vehicles — 30% of them more than 20 years old — now ply the city streets.

Mexico city’s geographic disadvantage

Geography conspires with human activity to produce a poisonous scenario. Located in the crater of an extinct volcano, Mexico City is about 2,240 metres above sea level. The lower atmospheric oxygen levels at this altitude cause incomplete fuel combustion in engines and higher emissions of carbon monoxide and other compounds. Intense sunlight turns these into higher than normal smog levels. In turn, the smog prevents the sun from heating the atmosphere enough to penetrate the inversion layer blanketing the city.

Geography conspires with human activity to produce a poisonous scenario. Located in the crater of an extinct volcano, Mexico City is about 2,240 metres above sea level. The lower atmospheric oxygen levels at this altitude cause incomplete fuel combustion in engines and higher emissions of carbon monoxide and other compounds. Intense sunlight turns these into higher than normal smog levels. In turn, the smog prevents the sun from heating the atmosphere enough to penetrate the inversion layer blanketing the city.

Solving this problem has been a priority of the Metropolitan Environmental Commission. Recent efforts to curb emissions have been relatively successful. In the 1990s, for instance, the government introduced air quality improvement programs — PIICA and PROAIRE — that include a rotating one-weekday ban on private car use. On days of high pollution, the ban extends to every second day and some manufacturing activities are curtailed. In addition, car owners must have their vehicles certified every six months. But if lead, carbon monoxide, and sulphur dioxide are now under control, pollution levels of other contaminants are still far above air quality standard