The city sits in a valley surrounded by mountains and volcanoes, which results in poor air circulation and a tendency for air pollutants to stagnate over the city. Due to the extremely rapid pace of urbanization in the twentieth century little consideration was given to environmental planning. By 1987, air quality had deteriorated so much that one day thousands of birds appeared dead on the sidewalks of the city. Environmentalists attributed this to air pollution. This shocking event encouraged authorities to implement measures to improve air quality. Most heavy industries (glass, car and steel factories) and oil refineries were relocated outside of the city and unleaded vehicle fuels were introduced.
Today, the air quality is in much better. Ozone and carbon dioxide levels are falling. Although the smog layer is visible nearly every day, its effects in terms of breathing and eye irritation are barely noticeable and it should not be cause for concern for visitors. Pollution is in maximum effect in the hot, dry season of spring, from late February to early May and there is a greenhouse effect that appears during winter from late November to early February. You can check the current air quality on the Atmospheric Monitoring System website . This government body established an index denominated IMECA (Metropolitan Index for Air Quality) in order to make the population aware of the current air pollution situation.
When the index exceeds 170 points, an "Environmental pre-contingency" is issued and people are asked to refrain from performing open-air activities such as sports. In the case of an "Environmental Contingency," only vehicles with a zero or double zero emissions sticker can circulate.
The Most Frequently Asked Travel Questions about Mexico City
Where To Stay & Best Hotels in Mexico City - updated Sep 2023
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Mexico City Travel Guide from Wikitravel. Many thanks to all Wikitravel contributors. Text is available under Creative Commons Attribution-ShareAlike 3.0, images are available under various licenses, see each image for details.
