Heterogeneous Uptake Kinetics of Volatile Organic Compounds on Oxide Surfaces Using a Knudsen Cell Reactor:  Adsorption of Acetic Acid, Formaldehyde, and Methanol on α-Fe₂O₃, α-Al₂O₃, and SiO₂

Abstract

The role of heterogeneous reactions on particulate matter present in the Earth's atmosphere remains an important question in tropospheric chemistry. It has been proposed in several modeling studies that mineral dust may provide reactive surfaces for trace atmospheric gases. Laboratory studies can provide some answers concerning the kinetics of these reactions, so that heterogeneous chemistry can be quantitatively assessed in atmospheric chemistry models. In this study, the heterogeneous uptake kinetics of several volatile organic compounds (VOCs) on oxide surfaces have been measured with a Knudsen cell reactor at 295 K. In particular, the heterogeneous uptake of acetic acid, methanol, and formaldehyde on α-Fe2O3, α-Al2O2, and SiO2 has been investigated. These VOCs are representative of some of the different types of oxygenated organics found in the atmosphere. The oxide particles used in this study are models for mineral dust found in the Earth's atmosphere. Initial uptake coefficients, γ0, have been extracted from the Knudsen cell data. The uptake kinetics have been measured as a function of sample surface area to ensure that realistic surface areas are used in the calculation of the uptake coefficient. Heterogeneous reaction rates are then compared to homogeneous reactions rates for gas-phase reactions involving acetic acid, methanol, and formaldehyde. From this comparison, the possible atmospheric implications of heterogeneous reactions involving these oxygenated organics are discussed.

Temperature Dependence of the Heterogeneous Reaction of Carbonyl Sulfide on Magnesium Oxide

“…[29][30][31][32][33] Therefore, the true uptake coefficients, γ t , can be calculated from where "slope" is the slope of the plot of γ versus sample mass in the linear regime (kg -1 ), A s is the geometric area (m 2 ) of the sample holder, and S BET is the specific surface area of the particle sample (m 2 ‚kg -1 ). 34 As shown in Figure 3, there was a strong linear dependence of uptake coefficients at the initial time γ(Ini) and at steady state γ(SS) versus sample mass. The correlation coefficients were 0.990 and 0.966, respectively.…”

Geocatalytic Uptake of Ozone onto Natural Mineral Dust

“…The determined γ 0 and γ ss of ozone on Gobi dust have been plotted as a function of initial ozone concentration [O 3 According to the atmospheric heterogeneous interaction studies, the absolute number of ozone molecules lost per second from gas phase due to the interaction of the ozone molecules with the mineral surface depends on the effective surface of the dust, the average molecular speed of ozone molecules, and the uptake coefficient [30][31][32][33]; this can be determined from Equation (1):…”

“…The approximation used in Equation (1) assumes the uptake probability γ ≪ 1, which is the case in the present paper. The uptake probability (γ) can be derived from Figure 1b and Equation (2) [30,31]:…”

Theoretical investigation on the role of mineral dust aerosol in atmospheric reaction: A case of the heterogeneous reaction of formaldehyde with NO 2 onto SiO 2 dust surface

“…HCHO is one of the most prevalent VOCs in the Earth's atmosphere. It can be produced by the photooxidation of most VOCs and serve as an important source of HO x radical (Lin et al, 2012), peroxy radicals, and peroxyacyl nitrates (Carlos-Cuellar et al, 2003). Therefore, its dual role makes it as an important species for testing the performance of photochemical oxidant models.…”

“…NO 2 is not only an important constituent of the natural unpolluted atmosphere, but also one of the major pollutants from anthropogenic sources such as motor vehicles (Power et al, 2011), power plants (Jurkat et al, 2011) and combustion process (Zhang et al, 2006). Thus, it has taken a great deal of research to the reaction of HCHO and NO 2 in the absence of SiO 2 (Ji et al, 2012;Xu and Lin, 2003) or to the adsorption performance of HCHO onto SiO 2 (Carlos-Cuellar et al, 2003;Iuga et al, 2008), but to our knowledge, no prior theoretical and experimental studies have been explored the heterogeneous reaction of HCHO with NO 2 in the presence of SiO 2 . The goals of this study are as follows: (i) find a reasonable theoretical method to model the heterogeneous reaction of VOCs; (ii) specify which species is more easily absorbed onto the mineral dust aerosol surface: organic or inorganic compounds; (iii) probe the role of mineral dust aerosol on the atmospheric reaction.…”