How Mountains Trap Air Pollution in Mexico City

The Bowl Effect: Topography and Smog

Mexico City sits in a high-altitude basin (2,240 m / 7,350 ft) surrounded by mountains on three sides. This topography acts like a lid, trapping pollutants emitted by vehicles, industry, and millions of residents.

Mechanism

• During the day, solar heating creates an inversion layer that prevents vertical mixing.
• Mountains block horizontal dispersion of pollutants.
• Result: Accumulation of ozone, particulate matter (PM2.5, PM10), nitrogen oxides, and volatile organic compounds.

Consequences

Persistent smog, reduced visibility, and elevated rates of respiratory and cardiovascular illness. The government has implemented driving restrictions (Hoy No Circula), industrial controls, and reforestation programs, but the geographic constraint remains a fundamental challenge.