Crucial VOCs influences on ozone formation in North China: A spatial perspective

With the increasing frequency of ozone (O₃) pollution episodes in China, there is a growing emphasis on understanding the contributions of precursors to O₃. Identifying key volatile organic compounds (VOCs) that drive O₃ formation has become a primary research focus. However, comprehending these key VOCs' distribution characteristics and patterns remains challenging. This study employs the convergent cross-mapping (CCM) method to identify and quantify causal relationships between 25 VOCs and O₃ simulated by WRF-Chem model. The results indicate that key VOCs identified by CCM can correspond well with those calculated based on observational data. Furthermore, the contributions and sources of various VOCs exhibits notable regional variations, showing a change with the O₃ formation sensitivity (OFS). In areas where OFS is strongly limited by VOCs, such as coastal ports and cities with concentrated resources or populations, alkenes, ketoaldehyde, and alcohols contribute more to O₃ formation. Meanwhile, the proportion of primary emission sources of oxygenated VOCs is relatively high (62.36–78.64 %), while secondary production sources are relatively low. Conversely, in regions where OFS is minimally limited by VOCs, such as agricultural areas in northern China, alkanes, aromatics, and phenols become more important. In this context, primary source contributions diminish while secondary source contributions rise to 19.1 %–45.6 %. Given North China's complex VOCs sources, this study suggests reducing key VOCs by targeting OFS characteristics within specific regions.