Validation of an experimental setup to study atmospheric heterogeneous ozonolysis of semi-volatile organic compounds

Abstract

Abstract. There is currently a need for reliable experimental procedures to follow the heterogeneous processing simulating the atmospheric conditions. This work offers an alternative experimental device to study the behaviour of semi-volatile organic compounds (SVOC) that presumably exhibit extremely slow reactivity (e.g. pesticides) towards the atmospheric oxidants such as ozone and OH. Naphthalene was chosen as a test compound since it was widely studied in the past and hence represents a good reference. Prior to ozone exposure, the gaseous naphthalene was adsorbed via gas-solid equilibrium on silica and XAD-4 particles. Then, the heterogeneous reaction of ozone with adsorbed naphthalene was investigated in specially designed flow tube reactors. After the reaction, the remaining naphthalene (adsorbed on particles surface) was extracted, filtered and analyzed by Gas Chromatography-Flame Ionization Detector (GC-FID). Thus, the kinetics results were obtained following the consumption of naphthalene. Using this procedure, the rate constants of heterogeneous ozonolysis of naphthalene (k O 3 silica =2.26 (±0.09)×10 −17 cm 3 molec −1 s −1 and k O 3 XAD−4 =4.29 (±1.06)×10 −19 cm 3 molec −1 s −1 ) were determined for silica and XAD-4 particles, at 25 • C and relative humidity <0.7%. The results show that the nature of the particles significantly affects the kinetics and that heterogeneous ozonolysis of naphthalene is faster than its homogeneous ozonolysis in the gas phase.

Ozone Decomposition on Kaolinite as a Function of Monoterpene Exposure and Relative Humidity

“…Consistent with field observations of adsorbed organics, laboratory work has demonstrated the facile formation of irreversibly adsorbed organic layers on mineral dust substrates exposed to semivolatile organic compounds, including monoterpenes. − Adsorbed surface concentrations can approach 5 × 10 18 molecules m –2 as determined by Lederer et al using DRIFTS and GC-MS analysis of several different types of mineral dust exposed to limonene . The ozonolysis of surface-adsorbed and aerosol-bound organics has been studied for polycyclic aromatic hydrocarbons, − self-assembled monolayers, , methacrolein and methyl vinyl ketone, and lignin pyrolysis products. − Reaction kinetics for many of these systems follow a Langmuir–Hinshelwood mechanism in which surface-adsorbed O 3 reacts with the coadsorbed organics. Therefore, reactive uptake depends not only on the structure of the adsorbed organic but also on the underlying substrate to which O 3 must first partition and the extent of organic surface coverage.…”

Photoenhanced degradation of veratraldehyde upon the heterogeneous ozone reactions

“…[49][50][51][52] ). In our previous works 53,54 and in this study as well we applied the modified L-H mechanism to describe the obtained experimental kinetic data (see later section 3.2.3). In the last ten years an important fraction of studies have dealt with these mechanisms (L-H and L-R) to describe heterogeneous reactions of atmospheric gaseous oxidants such as O 3 , NO 2 , with different classes of organic compounds adsorbed to either a liquid or solid surface.…”

Continuous Flow Ozonolysis in a Laboratory Scale Reactor

“…Recently, continuous-flow processing and microreactor technology have gained increased attention as valuable alternatives to batch protocols. , Dedicated flow reactors have been employed successfully in the past for performing highly exothermic reactions or in cases where hazardous (explosive, toxic) reagents or intermediates are involved. , The small reactor volumes and high heat transfer rates characteristic of these devices can mitigate the risks normally experienced in a batch process. , Therefore, the concept of continuous flow ozonolysis appears to be highly attractive. In recent years, several dedicated flow/microreactor devices have been described in the literature, able to effectively perform ozonolysis reactions for specific applications. − Nonetheless, the development of a general purpose laboratory scale continuous flow ozonolysis system is still in its infancy.…”