## 4 Results
### The Relative Importance of Explanatory Variables to O\({}_{3}\) Pollution  
Figure 3 presents the relative significance of the explanatory variables for surface ozone in the different surface ozone estimation models. Figure 3 illustrates the comparative importance of the explanatory variables in predicting the surface ozone concentrations across the various models employed for ozone estimation. This representation provides insight into which variables play a more substantial role in the modeling of surface ozone levels. The culmination of the quantitative estimation for the two surface ozone models revealed that VOCs, which include C\({}_{3}\)H\({}_{8}\), C\({}_{5}\)H\({}_{8}\), CH\({}_{4}\), H\({}_{2}\)O\({}_{2}\), OH, and PAN, were the principal contributors to O\({}_{3}\) pollution in the NCP, with the relative importance value for regional MDA8 concentration surpassing 23.34%. These results distinctly indicated that ozone pollution in the NCP was predominantly governed by VOCs. Among the six VOCs identified, C\({}_{3}\)H\({}_{8}\) and H\({}_{2}\)O\({}_{2}\) emerged as the most substantial contributors, with their relative importance values exceeding 4.26% and 4.08%, respectively. The remaining four VOCs including C\({}_{5}\)H\({}_{8}\), OH, PAN, and CH\({}_{4}\) were found to contribute more than 3.96%, 3.88%, 3.57%, and 3.54%, respectively. Furthermore, the relative importance of NO\({}_{2}\) (encompassing both S5P NO\({}_{2}\) and CAMS NO\({}_{2}\)) across the four models was found to exceed 7.35%, while that of CAMS-NO\({}_{\chi}\) was determined to be over 2.82%. This indicates that NO\({}_{\chi}\), which includes NO\({}_{2}\), is the second most critical factor in controlling surface ozone pollution within the NCP. Except for VOCs and NO\({}_{\chi}\), HCHO, either sourced from S5P or the CAMS, was recognized as a significant contributor to surface ozone pollution within the region. The relative impact of HCHO was found to exceed 5.64%, highlighting its critical role in the formation of ozone at the ground level. Regarding the meteorological factors, nine variables were considered including T, WS, WD, RH, BLH, UV, TCC, TP, and SP. Within the nine meteorological factors, WD, WS, RH, and T were the four most critical factors influencing O\({}_{3}\) pollution, and their relative importance was more than 3.35%. High temperatures, low wind speeds, and stable atmospheric conditions as well as downwind regions of polluted air masses were recognized as conducive to the photochemical production of ambient O\({}_{3}\), and this has been confirmed by previous studies [30; 31; 32; 33; 34]. Moreover, UV, BLH, and TCC were acknowledged as three principal factors affecting O\({}_{3}\) pollution in the NCP. This is attributed to the fact that intense UV radiation provides favorable conditions for the photochemical generation of ambient O\({}_{3}\), while BLH influences the vertical mixing of polluted air masses [1; 35]. The quantity of cloud cover impacts the reflection and scattering of light in the atmosphere, subsequently altering the rate of ozone production [36; 37; 38]. Additionally, TP and SP were also found to play a significant role in O\({}_{3}\) pollution, aligning with the findings of prior studies [39; 40; 41]. Except for the established influences of ozone precursors and weather elements, the NDVI has also been acknowledged as playing a significant role in ozone pollution. This effect is thought to result from the increased release of bioisoprene from plants, which subsequently leads to higher ozone concentrations [42; 43]. Furthermore, the DEM, LULC, and POPU have been identified as influential factors in surface ozone pollution [42; 44; 45]. Generally, VOCs and NO\({}_{\chi}\) emerged as the predominant factors influencing O\({}_{3}\) pollution in the NCP. The implementation of strategies to reduce VOCs and NO\({}_{\chi}\) emissions was instrumental in markedly decreasing O\({}_{3}\) pollution levels, thus aiding in the control of ozone pollution.