Interactions of ozone with organic surface films in the presence of simulated sunlight: impact on wettability of aerosols

Abstract

Heterogeneous reactions between organic films, taken as proxies for atmospheric aerosols, with ozone in presence of simulated sunlight and the photosensitizer 4-carboxybenzophenone (4-CB) were observed to alter surface properties as monitored by contact angle during the reaction. Attenuated total reflectance Fourier transform infrared spectroscopy (FTIR-ATR) was used in addition for product identification. Two types of model surfaces were systematically studied: 4-CB/4-phenoxyphenol and 4-CB/catechol. Solid organic films made of 4-CB/catechol were observed to become hydrophilic by simultaneous exposure to ozone and simulated sunlight, whereas organic films made of 4-CB/4-phenoxyphenol become hydrophobic under the same conditions. These changes in contact angle indicate that photo-induced aging processes involving ozone (such as oligomerisation) not necessarily favour increased hygroscopicity of organic aerosols in the atmosphere. The ratio between hydrophobic and hydrophilic functional groups should reflect the chemical property of organic films with respect to wettability phenomena. Contact angles and surface tensions of the exposed organic film made of 4-CB/4-phenoxyphenol were found to correspond to the hydrophobic/hydrophilic ratios obtained from the FTIR-ATR spectra.

Key role of organic carbon in the sunlight-enhanced atmospheric aging of soot by O2

“…At the same time, a prominent increase in the intensities of the bands at 1,720, 1,591, and 1,241 cm −1 indicates the formation of several oxygen-containing species, such as carbonyl C=O and ether C-O (2,30,31,34). These results definitely demonstrate that sunlight can significantly enhance the heterogeneous reactions of soot with O 2 .…”

Influence of Combustion Conditions on Hydrophilic Properties and Microstructure of Flame Soot

“…Surface free energies are extremely important since they not only determine the strength of interaction between water and solid surfaces but also control the dynamics of molecular self-assembly, wetting, spreading, and adhesion. 31 Therefore, surface free energies are taken as a key factor to understanding the mechanism of surface-based phenomena. The solid surface tension γ sv , which is proportional to surface free energy, can be determined using Young's equation.…”

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

“…In terms of particle aging, this photochemistry leads to enhanced rates for the initial oxidation process but also initiates secondary, radical chain reactions that lead to high molecular weight products (Rouviere et al, 2009). Depending on the substrate the hydrophilicity of organic surfaces changes, which is important for CCN activation of organic particles (Nieto-Gligorovski et al, 2008;Zelenay et al, 2011). Related to these effects, on inorganic substrates, similar photochemistry supports renoxification of nitrate lost through heterogeneous reaction of HNO 3 with mineral dust ) via its photocatalytic reduction induced by titanium and iron oxides (Ndour et al, 2009a, b).…”