Unveiling the Formation of Atmospheric Oxygenated Organic Molecules under Anthropogenic-Biogenic Interactions: Insights from Binned Positive Matrix Factorization on Multi-Subrange Mass Spectra

Abstract. Oxygenated organic molecules (OOMs), which are low-volatility intermediates produced via volatile organic compound (VOC) oxidation, play a critical role in secondary organic aerosol (SOA) formation through gas-to-particle conversion. Despite recent advancements in OOM characterization, the high complexity of OOM spectra poses a significant challenge in the interpretation of their sources. This study investigates OOM formation in a Chinese megacity using an improved analytical strategy that integrates binned Positive Matrix Factorization on multiple sub-range mass spectral analysis. Unlike traditional approaches that handle mass spectral peak identification and chemical interpretation sequentially, our method simultaneously optimizes both, reducing uncertainties associated with peak assignment and chemical analysis. The method successfully identified 2571 OOM molecules and systematically revealed major OOM formation pathways through 11 distinct factors: five daytime photochemical processes, four nighttime NO₃-driven oxidation processes, and two regional mixed sources. Notably, this approach enabled the successful separation of sesquiterpene oxidation products in ambient measurements—compounds previously unidentified by traditional full-mass-range analysis due to their weak signals. The method captured dynamic changes in OOM composition under varying environmental conditions, demonstrating the influence of temperature and NO_x levels on OOM formation, as well as the volatility-dependent patterns influenced by condensation sink. This improved analytical strategy provides new insights into atmospheric OOM chemistry and establishes a robust foundation for future studies of VOCs-OOMs-SOA conversion mechanisms.