An Observation-Based Methodology and Application for Future Atmosphere Secondary Pollution Control via an Atmospheric Oxidation Capacity Path Tracing Approach

Abstract. As China's emission reduction efforts enter a plateau phase due to the slow decline of secondary pollutants, existing control strategies face diminishing returns. Atmospheric Oxidation Capacity (AOC), a key driver of secondary pollutant formation, represents a critical yet underutilized target for more effective control. The Atmospheric Oxidation Capacity Path Tracing (AOCPT) approach was proposed in this study. This approach quantitatively traces AOC to its precursors and sources, thereby facilitating the coordinated control of secondary pollution, by integrating three modules: a Radiation Equivalent Oxidation Capacity (REOC) method to quantify precursor species contributions, a Relative Incremental AOC (RIA) metric derived from a coupled box-receptor model to assess source impacts, and a modified source apportionment technique to resolve the respective contributions of both precursor species and sources to AOC. Successfully validated in a field study in Changzhi, China, AOCPT identified industrial processes (26.8 %) and diesel vehicle emissions (24.1 %) as the dominant AOC sources in a case city, driven largely by their trans-2-butene emissions (49.3 % and 20.6 % of total trans-2-butene, respectively). Crucially, secondary organic aerosols (SOA) were inadvertently enhanced by ozone (O₃)-targeted abatement, an AOC-centric strategy enables the co-mitigation of both pollutants. By enabling the precise regulation of AOC through direct quantification of precursor and source roles, the AOCPT approach facilitates the synergistic control of secondary pollutants. It provides a robust technical pathway and theoretical foundation to overcome current challenges in air quality management.