Diagnosis of ozone formation sensitivity in the Mexico City Metropolitan Area using HCHO/NO2 column ratios from the ozone monitoring instrument

•OMI data analysis of the HCHO/NO2 showed changes in the ozone formation sensitivity.•Ozone formation sensitivity changed from NOx/Transitional to VOC limited.•Decreasing VOC emissions and increasing NO2 emissions caused the regime changes.•Regulating the VOC emissions would be the approach for reducing ozone levels.