Ozone Uptake by Clay Dusts under Environmental Conditions

Abstract

Clay is the most emitted type of dust in the atmosphere and offers a large surface for heterogeneous interactions with atmospheric compounds. In this study, we focus on the uptake of ozone (O 3 ) by montmorillonite and kaolinite dust samples at atmospheric pressure in a coated-wall flow tube reactor. The influence of relevant environmental parameters, such as O 3 concentration, relative humidity, and temperature, is determined. A mechanism for O 3 interaction with the surface sites of clays is described, and atmospheric implications are discussed. Although the impact of O 3 uptake by fresh clay dust seems limited in the atmosphere, this work highlights the need to consider relevant and thoroughly defined uptake coefficients in models. Moreover, the presence of a pressure-dependence in the mechanism of O 3 uptake by dust suggested in this work helps reconciling measurements made at atmospheric pressure with those performed at low pressure in Knudsen cells.

Uptake and surface chemistry of SO2 on natural volcanic dusts

“…More information about influence of humidity on the steady state uptake of SO 2 on the surface of volcanic glass and ash is necessary to obtain a more comprehensive picture. While the increase in the SO 2 uptake with the increase of relative humidity is observed for a number of samples, it is not at all the case for the uptakes of other species, such as nonpolar volatile organic compounds (Romanias et al, 2016), hydrogen peroxide (H 2 O 2 ) (Romanias et al, 2012) or ozone (O 3 ) (Lasne et al, 2018). In fact, the uptake coefficient can decrease with increased humidity, such as the case for the steady state uptake of O 3 on montmorillonite clay dust reflecting the tendency for the molecules in question and molecules of water to compete with each other for the sorptive sites on the clay surface (Lasne et al, 2018).…”

“…The setup was described in detail in a previous paper (Lasne et al, 2018) it mainly consists of three parts; (i) the gas mixing line, (ii) the reactor and (iii) the analytical device. The gas preparation line is used for the mixing of zero dry/humid air with SO 2 resulting in a flow with the desired proportion of RH and SO 2 concentration.…”

“…In the absence of the generally accepted understanding of the nature of tailing and for the practical reasons the following pragmatic approach was adopted. Steady state is considered to be reached when the variation of the signal falls within 1.5% of its value for at least 3 h. On average it takes about 12 h to reach the steady state under 30% humidity, which is much longer than 1 h needed to achieve a steadystate for the uptake of ozone by clay dust (Lasne et al, 2018).…”

“…The measurements of [SO 2 ] at steady-state and at the initial level, [SO 2 ] 0 , together with the knowledge of the parameters defining our setup are necessary to conduct the analysis leading to the determination of the uptake coefficients under equilibrium conditions, γ ss (Lasne et al, 2018). Assuming first order kinetics for the uptake of SO 2 by v-dust surfaces, the observed constant of reaction, k obs (in s −1 ), is determined by (1):…”

“…The uptake of atmospheric relevant concentration of SO 2 (i.e. ≈ 75 ppb) by the surface of five selected v-dusts under typical atmospheric conditions of ambient temperature, pressure and 30% RH was investigated using the flow tube reactor (Lasne et al, 2018). A typical uptake profile depicted in Fig.…”