Competing multiple oxidation pathways shape atmospheric limonene-derived organonitrates simulated with updated explicit chemical mechanisms

Abstract. Organonitrates (ONs) are key components of secondary organic aerosols (SOAs) with potential environmental and climate effects. However, ON formation from limonene, a major monoterpene with unique structure, and its sensitivity to oxidation pathways remain insufficiently explored due to the absence of models with explicit chemical mechanisms. This study advances the representation of limonene-derived ON formation by incorporating 90 gas-phase reactions and 39 intermediates across three oxidation pathways (O3, OH, NO3) into both a chemical box model and a global model. Box model sensitivity experiments revealed that competition among major oxidation pathways, coupled with the high yield of limonene-derived ON from O3-initiated oxidation, leads to increased limonene-derived ON production when the O3-initiated pathway is enhanced, whereas strengthening the OH- or NO3-initiated pathways reduces ON formation. Compared to the box model, the global simulation exhibits stronger nonlinear responses and great spatiotemporal variability in limonene-derived ON formation across different oxidation pathways. This is primarily driven by the complex distribution of precursors and oxidants, as well as the change in dominate chemical pathways under various meteorological conditions. In the presence of the other two pathways, increasing the O3- or NO3-initiated oxidation pathway reduces the global limonene-derived ON burden by 19.9 % and 17.3 %, respectively, whereas enhancing the OH-initiated pathway increases it by 44.7 %. Limonene-derived ON chemistry developed in this study not only enhances the global model's ability to simulate ON formation evaluated through comparison with observations but also demonstrates an approach based on explicit chemical mechanisms that establishes a methodological framework for simulating the chemical formation processes of SOA.