[Quantifying the Influence of Meteorological Factors on Summer Ozone Concentration in the Main Urban Area of Lanzhou...

Meteorological conditions have a significant impact on the concentration variations of ozone （O₃） and its precursors. Quantifying the impact of different meteorological factors on O₃ concentrations is crucial for formulating and optimizing prevention and control strategies for near-surface O₃ pollution. This study collected hourly near-surface O₃ concentration data and meteorological data from the main urban area of Lanzhou City during the summers from 2019 to 2023. Using an XGBoost-based meteorological normalization method， the impact of meteorological conditions on O₃ concentrations was decoupled and quantified. Subsequently， the XGBoost-SHAP model was introduced to quantitatively analyze the contributions of various meteorological factors to O₃ concentrations. The results indicate that the continuous increase in near-surface O₃ concentrations in the main urban area of Lanzhou City during the summers from 2019 to 2023 was due to a combination of meteorological conditions and precursor emissions. Meteorological conditions were the primary factor contributing to the continuous rise in O₃ concentration from 2019 to 2021. The relatively unfavorable meteorological conditions from 2019 to 2020 and from 2020 to 2021 resulted in increases in ambient O₃ concentrations of 3.828 and 7.378 μg·m^-3， respectively. The meteorological conditions improved between 2021 and 2022 and again between 2022 and 2023， resulting in decreases in O₃ concentrations by 0.348 and 0.768 μg·m^-3， respectively. The increase in O₃ concentration during these two years was mainly related to changes in precursor emissions. Through SHAP model analysis， it was found that boundary layer height （BLH）， 2-meter temperature （T2m）， downward surface ultraviolet radiation （UVB）， relative humidity （RH）， and surface net solar radiation （SSR） were the key meteorological factors influencing the summer near-surface O₃ concentrations in the main urban area of Lanzhou City. The annual contribution rates of these factors to O₃ concentrations remained stable within the range of 71.82% to 73.65%. T2m， BLH， and UVB were positively correlated with O₃ concentrations， while RH was negatively correlated with O₃ concentrations. The contribution of SSR to O₃ concentrations exhibited a unimodal pattern， with both excessively high and low levels inhibiting O₃ production. The contribution values of various meteorological factors to summer ozone concentrations in the main urban area of Lanzhou City changed over time. Fluctuations in T2m and RH were the main reasons for the interannual variations in the meteorological contribution to summer O₃ concentrations in the main urban area of Lanzhou City from 2019 to 2023.