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 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. In this study, the Atmospheric Oxidation Capacity Path Tracing (AOCPT) approach was proposed to quantitatively trace AOC to its precursors and sources. It facilitates coordinated control by integrating three core modules. It employs a Radiation Equivalent Oxidation Capacity (REOC) method to quantify precursor species contributions. Meanwhile, it utilizes a Relative Incremental AOC (RIA) metric derived from a coupled box-receptor model to assess source impacts. Finally, a modified source apportionment technique was applied to resolve the respective contributions of both precursor species and sources to AOC. Successfully applied in a field study in Changzhi, China. The AOCPT identified industrial processes (26.8 %) and diesel vehicle emissions (24.1 %) as the dominant AOC sources, driven largely by trans-2-butene. Notably, conventional sensitivity analyses based on ozone (O3)-targeted strategies were found to underestimate the contributions of these two sources by 28.7 % and 48.5 %, respectively. Furthermore, while O3-targeted abatement inadvertently enhanced secondary organic aerosols (SOA), an AOC-centric strategy enabled 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.