Ethylamine-Driven Amination of Organic Particles: Mechanistic Insights via Key Intermediates Identification

Abstract. Atmospheric amines critically contribute to secondary aerosols formation via heterogeneous reactions, yet the molecular mechanisms governing heterogeneous amination chemistry of aerosols remain unclear. Here, we utilize an integrated tandem flow-tube system coupled with online ultrahigh-resolution mass spectrometry to elucidate the amination chemistry of ethylamine (EA) with representative organic aerosol components, including C₂₀-C₅₄ secondary ozonides (SOZs), C₁₇-C₂₇ carboxylic acids, and aldehydes. Our experiments provide evidence for the formation of four key intermediates: hydroxyl peroxyamines, amino hydroperoxides, peroxyamines, and amino ethers, which mediate SOZs conversion to hydroxyimines, amides, and imines. Furthermore, dihydroxylamines and hydroxylamines are identified as characteristic intermediates in carboxylic acids and aldehydes amination. Quantitative heterogeneous reactivity measurements (Δγ_eff) reveal that SOZs exhibit a pronounced inverse dependence on carbon chain length, e.g., C₂₁ SOZ (Δγ_eff = 1.0 × 10^-4) > C₄₉ SOZ (Δγ_eff = 5.7 × 10^-6), with consistently lower reactivity than acids and aldehydes, e.g., C₁₇ acid (Δγ_eff = 2.3 × 10^-4). The amination mechanism of SOZs is initiated by EA addition, followed by either hydroxyl peroxyamines-mediated dehydration yielding hydroxyimines and amides, or amino hydroperoxides-driven H₂O₂ elimination forming imines. For carboxylic acids and aldehydes, EA addition leads to dihydroxylamines and hydroxylamines formation, which subsequently dehydrate to produce amides and imines. These findings provide a mechanistic framework for understanding amine-driven aerosol aging processes that affects atmospheric chemistry, air quality, and climate systems.