01 · The problem
What is happening
Mexico City sits in a high basin surrounded by mountains, where intense sunlight and weak ventilation favour ozone formation from vehicle and industrial emissions. Once considered one of the most polluted cities in the world, it made significant progress from the 1990s through fuel reformulation, catalytic converters and driving restrictions (Hoy No Circula). Ozone remains a persistent problem, and the metropolitan environmental commission activates environmental contingency phases during severe episodes.
High severity. Serious, widespread effects requiring sustained action. Severity is descriptive editorial metadata summarising documented effects. It is not a measured index or a score.
02 · Causes
Why it is happening
- 01
Vehicle emissions
A large vehicle fleet emits ozone precursors.
- 02
Basin topography and altitude
Mountains and inversions limit dispersion; strong sunlight drives photochemistry.
- 03
Industry and solvents
Industrial and household solvents emit volatile organic compounds.
03 · Impacts
Who and what it affects
- 01
Respiratory health effects
Ozone irritates airways and aggravates asthma.
- 02
Activity restrictions
Contingency phases restrict driving and outdoor activity.
04 · Solutions
Documented approaches
Hoy No Circula
Driving restrictions based on licence plate and vehicle emissions.
Expected effectReduces traffic emissions, particularly from older vehicles.
Public transport expansion
Metrobús, cable cars and cycling infrastructure.
Expected effectProvides alternatives to private cars.
Regional environmental commission
Coordination through the Comisión Ambiental de la Megalópolis.
Expected effectAddresses pollution across the wider region.
05 · Key indicators
What can be measured
No reliable quantitative indicator is included for this issue. TerraLens shows figures only where a credible source supports them — consult the sources below for current data.
06 · Sources
Where this comes from
- [1]Secretaría del Medio Ambiente de la Ciudad de MéxicoGobierno de la Ciudad de Méxicosedema.cdmx.gob.mx(opens in a new tab)
- [2]WHO global air quality guidelinesWorld Health Organization · Sept 2021who.int(opens in a new tab)
Links open the publishing organisation's site. Some point to the publisher's main page, where the named report or dataset can be found.