Oxidation of Atmospheric Humic Like Substances by Ozone: A Kinetic and Structural Analysis Approach

Abstract : This work explores the heterogeneous reaction between HUmic-LIke Substances (so-called HULIS) and ozone. Genuine atmospheric HULIS were extracted from aerosol samples collected in Chamonix (France) in winter and used in coated flow tube experiments to evaluate heterogeneous uptake of O-3 on such mixtures. The uptake coefficient (gamma) was investigated as a function of pH (from 2.5 to 10), O-3 concentration (from 8 to 33 x 10(11) molecules cm(-3)), relative humidity (20 to 65%) and photon flux (from 0 to 1.66 x 10(15) photons cm(-2) s(-1)). Reactive uptake was found to increase in the irradiated experiment with pH, humidity and photon flux. The extract was characterized before and after exposure to O-3 and/or UV light in the attempt to elucidate the effect of the photochemical aging. Carbon content measurements, UV-is spectroscopy and functional groups analysis revealed a decrease of the UV absorbance as well as of the carbon mass content, while the functionalization rate (COOH and C=O) and therefore the polarity increased during the simulated photochemical exposure.