Normally, the temperature decreases with altitude, allowing air pollutants to rise and disperse. During inversion episodes, warmer air at higher altitude traps air pollutants at the ground. By merging vertical temperature profile data from NASA with pollution monitors and health care records, we show that inversions increase the PM10 levels by 25% and children’s respiratory health problems by 5.5%. Low-income children are particularly affected, and differences in baseline health seem to be a key mediating factor behind the effect of pollution on the SES health gap. Policies that improve dissemination of information on inversion status may hence improve child health, either through private action or via policies that curb emissions during inversion episodes.