VOCs-driven ozone extremes during dry and wet heatwaves in the Jiangsu–Shandong–Henan–Anhui Boundary: Integrating meteorological forcings and SHAP interpretation

Abstract

Climate change is driving more frequent and severe dry and wet heatwaves, yet a clear picture of how each type influences ozone (O₃) production in areas characterized by intricate industry and geography are still lacking. This study examines O₃ formation during heatwaves, focusing on interactions among meteorological factors, atmospheric chemistry, and pollutant emissions in a unique industrial area at the junction of Jiangsu, Shandong, Henan, and Anhui provinces of northern China in summer 2022 and 2023. This study integrates hourly data of temperature, relative humidity (RH), solar radiation (SF), 115 VOCs, and other atmospheric pollutants, and quantifies the contribution of each factor using machine learning models combined with SHAP. Results show that SF is the main driver influencing O₃, contributing 13.7 μg/m³ during dry heatwaves and 5.0 μg/m³ during wet heatwaves. RH and atmospheric diffusion conditions are distinct between the dry and wet heatwaves. PMF indicates that industrial emissions dominate O₃ formation during dry heatwaves while biogenic VOCs dominate during wet heatwaves. For VOCs, during dry heatwaves the SHAP values for styrene, propene and isoprene were 9.1, 4.4 and 3.8 μg/m³, respectively, significantly affecting O₃ formation; In wet heatwaves, styrene, propene and acetaldehyde dominate, with SHAP values of 6.7, 4.3 and 2.5 μg/m³ respectively. Diurnal analysis indicates that while styrene and propene boost O₃ during daytime (9:00–17:00), their effects reverse in the early morning (6:00–8:00). In contrast, isoprene contributes positively (2.85 μg/m³) during dry heatwaves and negatively (−2.92 μg/m³) during wet ones. Overall, the study offers an efficient framework for understanding O₃ formation in extreme weather and informs targeted pollution control strategies.