Valley of Mexico - History of Human Habitation - Air Pollution

Air Pollution

Mexico City is vulnerable to severe air pollution problems due to its altitude, its being surrounded by mountains and the winds patterns of the area. The altitude, with its low oxygen levels makes for poor combustion of fossil fuels leading to unsafe levels of nitrogen oxides, hydrocarbons, and carbon monoxide. The valley is surrounded by mountain ranges with one small opening to the north. The surrounding mountains and climate patterns here make it difficult to clear out the smog produced. The valley has internal wind patterns with circulate around the valley without a prevailing wind to push contaminants in a single direction. The most significant climatic phenomena here is "thermal inversion," which is prevalent in the winter months when the cooler air of the valley is trapped by relatively warmer air above. Adding to this is that prevailing winds outside the valley move from north to south, in through the Valley's one opening, where incidentally most of the region's industry is located. These factors diminish in the summer and the situation is helped by the arrival of the rainy season, but the valley's southern latitude and the abundance of sunlight allows for dangerous levels of ozone and other dangerous compounds.

While still considered one of the most polluted places on the planet, the valley's air pollution problems are not as bad as they were several decades ago. One major problem that was brought under control was the lead contamination in the air with the introduction of unleaded gasoline. Two other contaminants that have been brought under control are carbon monoxide and sulfur dioxide. The contamination problems that remain are primarily with ozone and fine particles (soot) (between 2.5 micrometers and 10 micrometers). Thirty to fifty percent of the time, Mexico City's levels of fine particles of ten micrometers, the most dangerous, exceed levels recommended by the World Health Organization. In the 1940s, before large-scale burning of fossil fuels in the area, the visibility of the valley was about 100 km (60 mi), allowing for daily viewing of the mountain ranges that surround the valley, including the snow-capped volcanoes of Popocatepetl and Iztaccihuatl. Since that time, the average visibility has come down to about 1.5 km (5,000 ft). Mountain peaks are now rarely visible from the city itself. While reduced visibility in the valley was due to sulfur emissions in the past, it is now due to fine particles in the air.

The effects on humans living in an enclosed, contaminated environment have been documented, especially by Nobel Prize winner Dr Mario J. Molina. He claims fine particle pollution is the greatest concern because of lung damage. According to him, the city's residents lose about 2.5 million working days every year due to health problems associated with fine particles.