Mexico City: The Country's Worst Air Pollution

Mexico City (CDMX) consistently ranks as Mexico's most polluted major city—and among the world's worst for PM2.5 and ozone.

Why CDMX?

• Basin topography: 2,240 m altitude, surrounded by mountains — traps pollutants.
• 21M+ metro population: 5M+ vehicles, dense industry, construction.
• Climate: Intense sun (ozone formation), dry season (Nov–May) = stagnant air.
• Sources: Vehicles (60%+), industry (refineries, power), area sources (cooking, dust).

Health Impact

~15,000 premature deaths/yr (IMCO). Asthma, CVD, lung cancer, cognitive decline in children. Contingencia Ambiental alerts trigger driving restrictions (Hoy No Circula), school closures, construction halts.

Policy Responses

• Hoy No Circula: Plate-based driving bans (incl. Saturday).
• Vehicle verification: Semiannual emissions testing.
• Metro/Metrobús/RTP expansion: 12 Metro lines, 7 BRT lines.
• EVs: Incentives, charging, electric taxis/buses.
• Refinery closure: Azcapotzalco (1991), Tula (partial).

Progress & Gaps

Lead (gasoline) eliminated. SO2 down 90%. But PM2.5 and O3 remain above WHO guidelines. 2023: 120+ contingency days. Megacity geography + growth = persistent challenge.

Other polluted: Monterrey (industrial), Guadalajara (vehicular), Tula (refinery). But CDMX = scale + basin = unique trap.