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

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 O3 on such mixtures. The uptake coefficient (γ) was investigated as a function of pH (from 2.5 to 10), O3 concentration (from 8 to 33 × 1011 molecules cm–3), relative humidity (20 to 65%) and photon flux (from 0 to 1.66 × 1015 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 O3 and/or UV light in the attempt to elucidate the effect of the photochemical aging. Carbon content measurements, UV–vis 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.