NH ₃ converts Criegee intermediates to nitrogenous organics

Abstract. Ammonia (NH3), the dominant alkaline gas in the atmosphere, plays a critical role in urban air quality, but its molecular-level interactions with organics remain poorly understood. Here, we uncover a hidden chemical pathway: NH3 efficiently scavenges stable Criegee intermediates (SCI) – critical zwitterions in organic aerosol formation. Using high-resolution Orbitrap mass spectrometry, we capture the first real-time evidence of NH3 reacting with styrene-derived C7-SCI to form a hazardous peroxide amine (C7H9O2N) while suppressing traditional SCI-driven aerosol components like benzoic acid and oligomers. Due to unstable bond of peroxide in the molecule, C7H9O2N can further decompose into more stable compounds (imine C7H7N and amide C7H7ON). This study discovered a critical reaction pathway for the formation of organic amines through the reaction of NH3 and SCI, which not only bridges a critical gap in understanding NH3's role in aerosol chemistry but also exposes a previously overlooked health risk from nitrogen-enriched particulate matter.