VOC Characteristics, Sources, and O3 Precursor Sensitivity During Severe Summer Photochemical Pollution in a Central China Megacity

Despite substantial reductions in precursor emissions, persistent summer ozone (O3) pollution remains a critical environmental challenge in the North China Plain. This study integrated O3 and volatile organic compound (VOC) data from the summers of 2014–2020 with an observation-based box model (OBM) to analyze O3 pollution trends, VOC composition, sources, and sensitivity in Zhengzhou. The results indicated a continuous intensification of summer O3 pollution, a progressive annual increase in polluted days, and an average annual concentration increase of 6.72 μg m−3 yr−1. Further, the average VOC concentration on polluted days was 11.7% higher than that on non-polluted days, with alkanes dominating the component distribution, followed by aromatic hydrocarbons, alkenes, and alkynes. Subsequently, a source-apportionment model (positive matrix factorization) was used to identify six VOC sources: motor vehicle emissions (28.4%), industrial emissions (23.2%), solvent use (16.0%), liquefied petroleum gas/natural gas use (15.8%), fuel combustion (11.4%), and biological sources (5.4%). The photochemical age method corrected VOC loss during atmospheric transport, revealing that the traditional O3-formation potential (OFP) method underestimated the contributions of alkenes and aromatic hydrocarbons, with isoprene, m/p-xylene, and ethylene as key species. Furthermore, multi-scenario simulations showed that solely reducing nitrogen oxides (NOx) emissions caused an O3 concentration rebound, while a 4:1 VOC to NOx reduction ratio provided optimal control. By identifying the causal drivers of O3 pollution in Zhengzhou, this study provides a scientific basis for designing precise emission-reduction strategies applicable to the North China Plain and analogous urban regions.