Mexico City Air Quality
CDMX: 21.9 million people in a high-altitude mountain basin with 5M+ vehicles. Once declared the world's most polluted city (UN, 1992), Mexico City has made remarkable progress — but ozone and PM2.5 still exceed WHO guidelines year-round.
Monthly AQI
March is worst — dry season + maximum UV = peak ozone. Rainy season (Jun–Sep) offers relief.
Key Stats
From “World's Most Polluted” to Work in Progress
In 1992, the United Nations Environment Programme declared Mexico City the most polluted city on Earth. Children were reportedly “taking drugs just to breathe.” Ozone exceeded safe levels on 355 days per year — essentially every day.
The cleanup came from a combination of policies that Mexico City implemented faster than most comparable cities:
- 1991: Mandatory catalytic converters + lead-free gasoline
- 1991: Hoy No Circula vehicle restriction (world's first)
- 1998: Ultra-low-sulfur gasoline (PEMEX Magna)
- 2000: Metrobús BRT system launched
- 2009: Ultra-low-sulfur diesel (15 ppm standard)
- 2010s: Metro expansion to 12 lines, 195 stations
The result: ozone dropped ~80% from 1990 peaks. PM2.5 fell ~50%. But rapid population growth and car ownership growth have offset some gains. Mexico City is a rare example of a megacity that genuinely improved — but the work is not done.
Health Advisory by Season
Avoid outdoor exercise 10am–6pm when ozone peaks. Sensitive groups should stay indoors during contingencias. Check SEDEMA's AIRE app for real-time data.
Best months for outdoor activity. Morning hours before rain are cleanest. Afternoon thunderstorms (3–5pm) flush pollutants. AQI typically Good to Moderate.
Improving air quality. Rain becomes less frequent and ozone starts to build again. Moderate conditions typical.
Cold dry air and winter inversions trap PM2.5. Vehicle emissions from cold starts are highest. Morning rush hours are especially polluted in the Tepito/Centro historic core.
Frequently Asked Questions
What is Mexico City's AQI in 2024?
Mexico City's annual average AQI in 2024 was approximately 88 (Moderate to Unhealthy for Sensitive Groups). PM2.5 averaged 18.9 μg/m³ — 3.8× the WHO annual guideline. Ozone is the primary pollutant of concern, especially March–May.
When is Mexico City's air quality worst?
March and April are typically the worst months. The combination of dry air, maximum UV radiation (high altitude = stronger UV), and stable atmospheric conditions produces the most intense ozone formation. Contingencias ambientales (emergency restrictions) are most common in March–May.
What is a Contingencia Ambiental in Mexico City?
A Contingencia Ambiental is an environmental emergency declared by SEDEMA when ozone exceeds 155 ppb or PM2.5 exceeds 75 μg/m³. During Phase 1 emergencies, pre-2000 vehicles without hologram exemption are restricted. Phase 2 extends restrictions to more vehicles and bans certain industrial activities.
Does Mexico City have good air quality compared to 30 years ago?
Yes, dramatically better. In 1991, Mexico City recorded 355 ozone standard exceedance days — effectively never meeting clean air standards. By 2024, exceedance days dropped to ~80–90 per year. PM2.5 fell ~50% since 1990. The improvement came from catalytic converters (1991), lead-free gasoline (1991), ultra-low-sulfur diesel (2009), and Metro/Metrobús expansion.
Is the air quality better in summer (rainy season) in Mexico City?
Yes. The rainy season (June–October) brings afternoon thunderstorms that wash pollutants out of the air and break up stagnant inversions. July–August are typically Mexico City's cleanest months. Afternoon rain also lowers ozone by reducing UV exposure.