Polar Nitrated Aromatic Compounds in Urban Fine Particulate Matter: A Focus on Formation via an Aqueous-Phase Radical Mechanism

• DOI: 10.1021/acs.est.2c07324
• Publication Date: 2023-03-20T20:49:30Z
• Authors: Xiaodi Shi; Xinghua Qiu; Ailin Li; Xing Jiang; Gaoyuan Wei; Yan Zheng; Qi Chen; Shiyi Chen; Min Hu; Yinon Rudich; Tong Zhu
• Keywords: Aqueous two-phase system

Polar nitrated aromatic compounds (pNACs) are key ambient brown carbon chromophores; however, their formation mechanisms, especially in the aqueous phase, remain unclear. We developed an advanced technique for pNACs and measured 1764 atmospheric fine particulate matter sampled urban Beijing, China. Molecular formulas were derived 433 compounds, of which 17 confirmed using reference standards. Potential novel species with up to four rings a maximum five functional groups found. Higher concentrations detected heating season, median 82.6 ng m-3 Σ17pNACs. Non-negative matrix factorization analysis indicated that primary emissions particularly coal combustion dominant season. While non-heating aqueous-phase nitration could generate abundant carboxyl group, was by significant association aerosol liquid water content. Aqueous-phase 3- 5-nitrosalicylic acids instead isomer 4-hydroxy-3-nitrobenzoic acid suggests existence intermediate where intramolecular hydrogen bond favors kinetics-controlled NO2• nitration. This study provides not only promising pNAC measurement but also evidence formation, facilitating further evaluation pNACs' climatic effects.