DRIFTS studies on the photodegradation of tannic acid as a model for HULIS in atmospheric aerosols.

摘要: Humic like substances (HULIS) are important components of atmospheric aerosols, yet little is known about their photochemical transformation and the role adsorbed water in this photochemistry. We report herein situ surface-sensitive spectroscopic studies on (1) photodegradation solid tannic acid, (2) structure before after photodegradation, (3) change hydrophilicity acid as a result Tannic (TA) was chosen synthetic proxy for HULIS because it has defined molecular structure. Photochemical were conducted using diffuse reflectance infrared spectroscopy (DRIFTS) function time (3 h), relative humidity (5–30%) total irradiance (7, 20, 290 W m−2 at 555 nm). Water adsorption isotherm measurements recorded which provided information interfacial thermodynamics adsorption. The TA resembles that interface with polar organic solvents. Difference spectral data collected during irradiation shows loss features 1700–1000 cm−1 range growth carbonyl blue shifted to starting material, suggesting oxidative formation aryl aldehydes. Under our experimental conditions, we observed no enhancement uptake unirradiated samples. implications results understanding heterogeneous photochemistry these reactions discussed.