Molecular characterization of carbonyl compounds in atmospheric fine particulate matters (PM2.5) in Beijing by derivatization with Girard's reagent T combined with positive-ion ESI Orbitrap MS

Carbonyl compounds in aerosols endanger human health, affect atmospheric light absorption and cloud condensation nuclei activity, and are important precursors of secondary organic aerosols, but their composition is poorly understood. In the present study, we developed a new analytical method to characterize carbonyl compounds in PM2.5 (particles with aerodynamic diameter <= 2.5 mu m) by chemical derivatization with Girard's reagent T combined with positive-ion ESI high resolution-mass spectrometry (HR-MS). Girard's reagent T selectively labels carbonyl compounds, and HR-MS provides accurate elemental composition of derivatives. This method realized the comprehensive molecular characterization of carbonyl compounds in PM2.5. Thousands of carbonyl formulas (2330) were identified, including aliphatic carbonyls and a series of aromatic carbonyls. This method was further applied to the quantification of carbonyl compounds in PM2.5 samples collected in summer and winter from 2016 to 2017. In winter, carbonyl compounds had the highest contribution to organic matter (10%) and PM2.5 (4%), respectively, and the concentration of carbonyls showed obvious seasonal variation characteristics: 2.04 mu g/m3 in winter and 0.35 mu g/m3 in summer. The detailed characterization of the molecular composition of carbonyl compounds in PM2.5 provides basic data for further evaluating its impact on the climate effect of organic aerosols.