Diverse Nitrogen‐Containing Organic Compounds in Cloud Water Formed via Nucleophilic Addition Reaction Between Carboxylic Acid and Ammonia

Abstract Cloud droplets serve as a significant sink for atmospheric organic matter due to gas‐liquid transformations and interfacial reactions, containing abundant nitrogen‐containing organic compounds (NOCs). However, the formation mechanisms of NOCs in the cloud process remain poorly understood. In this study, we used UHPLC‐Q‐ToF‐MS for nontargeted analysis of cloud water samples collected at the summit of Mount Shanghuang in 2023. A total of 1,320 and 870 soluble organics molecular formulas were identified in the ESI+ and ESI− modes, respectively. These compounds are classified into seven groups, including CHO, CHN, CHON, CHNS, CHONS, CHS, and CHOS, respectively. CHON compounds were the most abundant, accounting for 52.1% in ESI+ and 47.2% in ESI−, highlighting their significance among the soluble organic species in cloud water. Nitrobenzene compounds predominated in ESI−, while chain amides were dominant in ESI+. Precursor matching analysis revealed that most chain amides are formed through nucleophilic addition reactions between ammonia and carbonyl groups, especially the monocarboxylic acids (with the high intensity from C 6 H 12 O 2 to C 20 H 40 O 2 ). The dominant species of monocarboxylic acids and monocarbamides (C 4 , C 16 , C 18 ) exhibited consistent patterns, with a notable prevalence of even‐numbered carbons. These results highlight that the liquid‐phase nucleophilic addition reactions between carboxyl groups and ammonia are crucial in cloud water chemistry.