资源环境科技发展态势分析平台

Abstract. The methanol extraction method was widely applied to isolate organic carbon (OC) from ambient aerosols, followed by measurements of brown carbon (BrC) absorption. However, undissolved OC fractions will lead to underestimated BrC absorption. In this work, water, methanol (MeOH), MeOH/dichloromethane (MeOH/DCM, 1:1, v/v), MeOH/DCM (1:2, v/v), tetrahydrofuran (THF), and N,N-dimethylformamide (DMF) were tested for extraction efficiencies of ambient OC, and the light absorption of individual solvent extracts was determined. Among the five solvents and solvent mixtures, DMF dissolved the highest fractions of ambient OC (up to ~95 %), followed by MeOH and MeOH/DCM mixtures (< 90 %), and the DMF extracts had significant (p < 0.05) higher light absorption than other solvent extracts. This is because the OC fractions evaporating at higher temperatures (> 280 °C) are less soluble in MeOH (~80 %) than in DMF (~90 %) and contain stronger light-absorbing chromophores. Moreover, the light absorption of DMF and MeOH extracts of collocated aerosol samples in Nanjing showed distinct time series. Source apportionment results indicated that the MeOH insoluble OC mainly came from unburned fossil fuels and polymerization processes of aerosol organics. These results highlight the necessity of replacing MeOH with DMF for further investigations on structures and light absorption of low-volatile BrC.