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Mexico City occupies a high-altitude basin in the Trans-Mexican Volcanic Belt, situated at approximately 2,240 meters (7,350 feet) above sea level, which profoundly shapes its air quality dynamics. The city is encircled by mountains on three sides—including the Sierra de las Cruces to the west and the Sierra Nevada to the east—creating a natural bowl that traps pollutants. This topographic confinement, combined with the urban heat island effect, exacerbates thermal inversions, particularly during the dry season, preventing the dispersion of emissions. The metropolitan area spans the Valley of Mexico, historically home to lakes like Texcoco, now largely drained but still influencing local humidity and dust storms. Proximity to agricultural zones in the State of Mexico and industrial belts in the eastern municipalities, such as Iztapalapa and Nezahualcóyotl, introduces additional particulate matter and chemical pollutants. The urban–rural gradient shows dense central districts with heavy traffic merging into peri-urban areas where informal settlements and wood-burning practices persist. Mexico City's location in central Mexico, far from major coastlines, limits maritime influences that might cleanse the air, making it reliant on seasonal wind patterns for ventilation. The high elevation reduces oxygen levels, intensifying the health impacts of pollution, while the surrounding volcanic soils contribute to road dust resuspension. This geographic setting, coupled with rapid urbanization, creates a persistent challenge for air quality management, as emissions accumulate in the basin with limited natural escape routes.

In Mexico City, air quality follows a distinct seasonal rhythm driven by meteorological patterns. During the dry winter months from November to February, cold temperatures and frequent thermal inversions trap pollutants close to the ground, leading to elevated levels of particulate matter and ozone precursors; sensitive groups, such as children and those with respiratory conditions, should limit outdoor exertion on calm, sunny days. Spring, from March to May, sees increasing temperatures and stronger winds that help disperse emissions, though occasional dust storms from the dried lakebed of Texcoco can spike particulate concentrations. The peak pollution months of June, July, and August coincide with the rainy season, where high humidity and intense sunlight accelerate photochemical reactions, forming ground-level ozone, while afternoon thunderstorms provide temporary cleansing but also contribute to flooding hazards—residents are advised to avoid strenuous activities during midday when ozone levels peak. Autumn, from September to October, offers relief as rains taper off and winds pick up, improving air quality and making it a favourable time for outdoor activities. Throughout the year, weather hazards like hailstorms and earthquakes can disrupt pollution monitoring, but the lack of a strong monsoon system means air stagnation is common. Health guidance emphasizes checking local air quality indices daily, using masks during high-pollution episodes, and planning activities for early mornings when pollution is lower, especially for vulnerable populations.