Determining Ozone Formation Sensitivity (OFS) and its driving factors is conducive to formulating effective ozone pollution control strategies. This study characterizes spatial and temporal variations in OFS by calculating the ratio of formaldehyde (HCHO, a maker of VOCs) to nitrogen dioxide (NO₂) in Henan Province from 2005 to 2016. The relationships of OFS with precursor emissions and meteorological factors are also analyzed.The Level 3 gridded retrievals from the Ozone Monitoring Instrument (OMI) were adopted to calculate Formaldehyde Nitrogen Ratio (FNR). Then, we took FNR<2.3 to indicate VOC-limited regime, FNR>4.2 to indicate NO_x-limited regime, and FNR between 2.3 and 4.2 to indicate transitional regime. Finally, the geographic detector model (GeoDetector) was used to quantify the influence of meteorological factors, anthropogenic emission precursors, and their interactions on OFS.The OFS in Henan Province changes in time and space. Most cities are transitional regimes in summer, where the O₃ concentrations are relatively higher. The drastic change in tropospheric NO₂ concentration determines the increase or decrease in VOC-limited regime. From 2005 to 2015, the FNR values decreased due to NO_x emission reduction, and OFS tended to be a transitional regime. After 2016, the FNR values increased, and OFS tended to be NO_x-limited. Anthropogenic emissions are the main driving factor of OFS in summer, which explains 40.5% of FNR variation on average. With the increase in CO (q = 0.46), PM_2.5 (q = 0.41), NO_x (q = 0.38), and NMVOC (q = 0.37) emissions, the FNR value decreases, which makes OFS more sensitive to VOC emissions in summer. Its sensitivity to NO_x emission reduction decreases. Surface net solar radiation (SSR, q = 0.321) and total column water (TCW, q = 0.302) are the top two meteorological factors influencing OFS in summer in Henan Province. As SSR increases, FNR decreases, which makes ozone formation more sensitive to VOCs. TCW has a complex effect on OFS. When TCW is less than 40 kg/m², FNR decreases with the increase in TCW, and ozone formation becomes more sensitive to VOCs. When TCW is larger than 40 kg/m², FNR increases with the rise in TCW, and ozone formation becomes more sensitive to NO_x. Interaction among factors enhances the ability to explain the change in OFS. In other words, each pair of factors has a greater influence on OFS than either. The interactions between precursors and meteorological factors have the most significant influence on OFS.Research results can enhance understanding of the photochemical process of ozone formation and provide a basis for formulating reasonable pollution reduction measures. However, the applicability of the OMI FNR indicator for the classification of ground-level ozone sensitivity in various regions still needs to be strengthened. Understanding the influence of driving factors and their interactions on changes in ozone sensitivity remains a challenge due to the nonlinear relationship between ozone sensitivity and its precursors and the complex reactions between meteorological conditions and precursors.

air pollution;ozone formation sensitivity;GeoDetector model;meteorological factors;anthropogenic emissions;interactive effects