河南省夏季臭氧生成敏感性及其驱动因素分析

明确当地臭氧生成敏感性变化的主控因子是制定有效臭氧污染控制策略的前提。采用卫星观测OMI FNR（Ratio of the tropospheric columns of Formaldehyde to Nitrogen dioxide，HCHO/NO₂）指示剂将河南省夏季臭氧生成敏感性OFS（Ozone Formation Sensitivity）划分为VOCs控制区、协同控制区和NOx控制区。基于地理探测器，量化气象条件、人为源前体物及其交互作用与OFS的关系。研究揭示：（1）河南省夏季OFS以协同控制区为主，区域内臭氧污染严重，仅次于VOC_S控制区。2005年—2015年，FNR值波动下降，OFS向协同控制区转变，主要受NO_X减排的影响。2016年之后，FNR值变大，OFS有向NO_X控制区转变的趋势。（2）人为源排放是OFS变化的主要驱动因子，平均可解释FNR变化的40.5%（q＝0.405）。若CO、PM_2.5、NOx和非甲烷挥发性有机物NMVOC（Non-methane Volatile Organic Compounds）的排放量增加，FNR减小，河南省夏季OFS向VOCs控制区转变，对NOx减排的敏感性降低。（3）地表净太阳辐射SSR（q＝0.321， Surface net Solar Radiation）和大气柱总水量TCW（q＝0.302， Total Column Water）是河南省夏季OFS变化的主要气象驱动因素。SSR增加，FNR减小，使臭氧生成对VOCs更加敏感。TCW对OFS变化的影响较为复杂，当TCW<40 kg/m²时，TCW增加，FNR减小，臭氧生成对VOCs更加敏感；当TCW>40 kg/m²时，TCW增加，FNR增大，臭氧生成对NOx更加敏感。（4）因子间的交互作用对OFS空间分布的驱动大于单一因子的独立作用，人为源前体物和气象因子的交互作用占主导地位。研究结果可加强对臭氧生成光化学过程的认识，为制定合理的污染减排措施提供依据。

Summertime ozone formation sensitivity and driving factors in Henan Province

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.