Why does Mexico City’s basin geography trap polluted air?

Mexico City’s basin geography traps polluted air primarily due to its high elevation and the mountains that enclose the valley on three sides, which significantly limit air circulation.12

This restricted airflow is further exacerbated by temperature inversion, a phenomenon where the normal atmospheric heat gradient is reversed. In this state, a layer of warmer air traps a blanket of cooler, polluted air near the ground, preventing the normal vertical movement of air that would otherwise disperse pollutants. Additionally, the city’s transformation into an urban heat island—caused by extensive paved surfaces that retain heat and impede moisture—contributes to these atmospheric conditions, making it difficult for the air to remain clean except during windy periods or the rainy season.231