Anthropogenic contributions to wintertime terpenes: Insights from multi-site online observations and machine learning...

Isoprene and monoterpenes are the most significant biogenic volatile organic compounds (BVOCs), which are generally regarded as being emitted primarily from vegetation, whereas their anthropogenic sources have received far less attention. This study combined wintertime observations from ten sites in Shenzhen in southern China, with a novel and universal data processing framework based on explainable machine learning to isolate anthropogenic influences on isoprene and monoterpenes. XGBoost models interpreted by SHAP identify acetonitrile as a key combustion tracer for isoprene and styrene as a dominant industrial and urban product tracer for monoterpenes. Scenario perturbation of these tracers yields robust source separation, showing that anthropogenic sources contributed 17.2% (daytime) and 25.4% (nighttime) to total isoprene, while contributing higher fractions to monoterpenes, reaching 39.3% (daytime) and 48.4% (nighttime). Importantly, anthropogenic terpenes explained more than 33% of both O₃ and SOA formation potentials during daytime and contribute 28.3% to the total NO₃ radical loss rate at night. Incorporating anthropogenic terpenes species sources into emission inventories would improve model predictive capability, while policy-based regulation of these controllable sources offers a practical pathway to mitigate secondary pollution in urban regions.