Relationship between the Chemical Structure of Humic Substances and their Hygroscopic Properties

Abstract

We investigated the relationship between the hygroscopic properties and chemical structures of humic and fulvic acids. Humic and fulvic acids were extracted from andosol, Canadian peat and Chinese weathered coal using the IHSS method. Fulvic-like organics produced by the ozone oxidation of humic acid were also prepared by a method reported previously. Their main chemical properties related to hygroscopicity were also studied by elemental analysis and the measurement of functional group contents. Humic and fulvic acids were allowed to stand under various relative humidity (RH) conditions and the amounts of water vapor adsorbed were measured by gravimetry. Water adsorption isotherms were similar for both humic and fulvic acids below RH 80%. Above 80%, water vapor adsorption of fulvic acids and fulvic-like organics increased considerably as compared with humic acids. Deliquescence was observed for all fulvic acids and fulvic-like organics at higher RH. The amount of water vapor adsorbed at 97% RH by humic substances from different sources was highly correlated with the ratio of oxygen to carbon contents. Permanent URL: http://hdl.handle.net/2047/d10006072