Scenario 4 An extreme condition exists when the air temperature actually increases with altitude. This corresponds to a very stable condition where any polluted warm air released near the ground will be trapped and not vertically dispersed. This condition is known as a thermal inversion There are several causes for thermal inversions and their duration varies from a few hours to many days Their occurrence in cities such as Los Angeles, Denver, and Mexico City is a major contributor to the air pollution problems of those citiesScenario 4 An extreme condition exists when the air temperature actually increases with altitude. This corresponds to a very stable condition where any polluted warm air released near the ground will be trapped and not vertically dispersed. This condition is known as a thermal inversion. There are several causes for thermal inversions, and their duration varies from a few hours to many days. Their occurrence in cities such as Los Angeles, Denver, and Mexico City is a major contributor to the air pollution problems of those cities