资源环境科技发展态势分析平台

Knowledge of the molecular‐level chemistry of brown carbon (BrC) is important in reducing the uncertainties in aerosol radiative forcing. Time ‐resolved ambient PM_2.5 samples were collected during a severe pollution episode in January 2017 over Xi’an, China for a comprehensive non‐target and full scanning of BrC molecules and their absorption properties using electrospray ionization–Fourier‐transform ion cyclotron resonance mass spectrometry (ESI‐FT‐ICR MS) combined with partial least squares regression (PLSR) analysis, which apportioned the overall UV absorption to individual molecules. The estimated absorption of CHNO and CHNOS molecules exhibited night‐time prevalence, whereas CHOS, CHNS, CHN, CHO, CHS, CH molecules presented a dynamic trend. Carbon conjugation was positively correlated with estimated absorption by CHO and CHNO molecules, while exhibiting a mixed relationship with CHNOS. Higher nitrogen content was associated with enhanced light‐absorption properties of BrC molecules, while higher oxygen and sulfur content appeared to be associated with photobleaching during secondary transformation.