Seasonal and temporal characterization of dissolved organic matter in rainwater by proton nuclear magnetic resonance spectroscopy

Dissolved organic carbon in rainwater was concentrated by two separate techniques and characterized by H-1-NMR. The total H-1-NMR integral of lyophilized rainwater was higher in every rain sample than that of C18 solid phase extracted samples and always contained a higher percentage integral in the region of protons bound to carbon atoms singly bound to oxygen (H-C-O), such as alcohols, polyols and carbohydrate-like compounds. C18 extracted samples had higher % integral in the alkyl region, consistent with reverse phase extraction of more hydrophobic components in rainwater. Differences in both the H-1-NMR integration and spectral pattern of lyophilized rainwater samples were especially apparent between spring and winter rains, with spring samples having higher percent carbohydrate (H-C-O) signal and winter rains having higher percent alkyl protons and a spectral pattern consistent with the presence of saturated fatty acids. Spring rains are characterized by lower % Alkyl signal coupled with higher % H-C-O than all other events while marine winter events appear in regions characterized by relatively high % Alkyl and average % H-C-O, consistent with increased abundance of fatty acids or fatty acid oxidation products. The H-1-NMR data presented in this manuscript are important because they provide spectral data relating to the source and chemical characteristics of dissolved organic carbon in rainwater as a function of season and air mass back trajectory. Published by Elsevier Ltd.