1H NMR studies of water- and alkaline-soluble organic matter from fine urban atmospheric aerosols.

Solution-state 1 H NMR spectroscopy was applied to characterize the structural features of water- and alkaline-soluble organic matter (WSOM and ASOM, respectively) sequentially extracted from fine urban atmospheric aerosols collected over different seasons. The objectives of this study were twofold: (i) to compare the functional characteristics of fine aerosol WSOM and the yet unknown ASOM, and (ii) to assess the sources of WSOM and ASOM at an urban location. The 1 H NMR analysis confirmed that the WSOM and ASOM fractions hold similar 1 H functional groups; however, they differ in terms of their relative distribution throughout the seasons. The winter and autumn samples have a less aliphatic and oxidized character and higher contributions from aromatic groups than those of warmer conditions. The urban aerosol WSOM and ASOM fractions do not fit the established 1 H NMR source apportionment fingerprints of marine, secondary, and biomass burning organic aerosols (OAs), exhibiting a smaller relative contribution of carbon-oxygen double bonds, which is indicative of a less oxidized character. These results confirm that the boundaries of the pre-established source categories, especially for secondary and biomass burning OAs, might be different at urban locations, suggesting the need to improve the 1 H NMR source apportionment model for including a new fingerprint for urban OAs. [ABSTRACT FROM AUTHOR]