Quantitative impacts of VOC sources on atmospheric oxidation capacity and O3 formation from a megacity in China

Abstract

Ozone (O₃) pollution has emerged as a significant environmental concern in recent years, particularly exacerbated by enhanced atmospheric oxidation during summer. While significant progress has been made in understanding the role of precursors in O₃ formation, studies focusing on the contributions of volatile organic compound (VOC) sources to O₃ formation mechanisms remain limited. This study integrated a photochemical box model incorporating the Master Chemical Mechanism (AtChem2-MCM) with Positive Matrix Factorization (PMF) to investigate VOC sources influences on O₃ photochemistry in Zhengzhou, a megacity in China. The sensitivities of the O₃-NOx-VOC sources were evaluated using the relative incremental reactivity (RIR), and priority sources for control were determined based on RIR, ozone formation potential (OFP), relative contribution (CTRB), and OH loss rate (L^OH). Results showed that the reaction HO₂ + NO (68.77%) dominated O₃ production, whereas OH + NO₂ (83.42%) was the primary pathway for O₃ loss. The atmospheric oxidation capacity (AOC) increased from 3.72 × 10⁷ molecules cm⁻³ s⁻¹ on non-O₃ pollution days to 5.69 × 10⁷ molecules cm⁻³ s⁻¹ on O₃ pollution days, with corresponding O₃ production and loss rates rising by 9.02 ppbv h⁻¹ and 0.54 ppbv h⁻¹, respectively. The RIR of mixed combustion sources (MC) was the highest among anthropogenic sources, and emergency prevention and control of O₃ should first reduce MC. Meanwhile, vehicular emissions (VE) accounted for the largest proportion of OFP, L^OH and CTRB, suggesting VE should be a long-term focus for O₃ mitigation efforts. Biogenic emissions (BE) also contributed significantly to O₃ formation and warranted attention. This integrated approach provides a robust theoretical framework for analyzing localized O₃ pollution and developing targeted mitigation strategies.