The adsorption of isopropanol on Gobi dust was investigated in the temperature (T) and relative humidity (RH) ranges of 273-348 K and <0.01-70%, respectively, using zero air as bath gas. The kinetic measurements were performed using a novel experimental setup combining Fourier-Transform InfraRed spectroscopy (FTIR) and selected-ion flow-tube mass spectrometry (SIFT-MS) for gas-phase monitoring. The initial uptake coefficient, γ, of isopropanol was measured as a function of several parameters (concentration, temperature, relative humidity, dust mass). γ was found independent of temperature while it was inversely dependent on relative humidity according to the empirical expression: γ = 5.37 × 10/(0.77+RH). Furthermore, the adsorption isotherms of isopropanol were determined and the results were simulated with the Langmuir adsorption model to obtain the partitioning constant, K, as a function of temperature and relative humidity according to the expressions: K = (1.1 ± 0.3) × 10 exp [(1764 ± 132)/T] and K = 15.75/(3.21+RH). Beside the kinetics, a detailed product study was conducted under UV irradiation conditions (350-420 nm) in a photochemical reactor. Acetone, formaldehyde, acetic acid, acetaldehyde, carbon dioxide, and water were identified as gas-phase products. Besides, the surface products were extracted and analyzed employing HPLC; Hydroxyacetone, formaldehyde, acetaldehyde, acetone, and methylglyoxal were identified as surface products while the formation of several other compounds were observed but were not identified. Moreover, the photoactivation of the surface was verified employing diffuse reflectance infrared fourier transform spectroscopy (DRIFTs).

For many years, the interaction between dust particles and water molecules has been a subject of interest for the atmospheric sciences community. However, the influence of the particle size on the hygroscopicity of mineral particles is poorly evaluated. In the current study, diffused reflectance infrared Fourier transform (DRIFT) spectroscopy is used to evaluate the in situ water adsorption on natural Arizona test dust (ATD) particles. Five different ATD size fractions, 0−3, 5−10, 10−20, 20−40, and 40−80 μm, are used, corresponding to the entire range of uplifted mineral particles in the atmosphere (<100 μm). N 2 sorption measurement, particle size distribution, and elemental analyses are performed to determine the physicochemical properties of the samples. The water adsorption experiments are conducted in an optical cell under flow conditions at room temperature and under the relative humidity (RH) range of 2− 90%. Experimental results are simulated with a modified three-parameter Brunauer−Emmett−Teller (BET) equation. Water monolayers are found to be formed at 13

Mineral dust is a major component of atmospheric aerosol that can impact both the climate and the oxidative capacity of the atmosphere. It has been recently suggested that heterogeneous processes on natural mineral dusts can act as a sink of volatile organic compounds (VOCs) and possibly as a sources of oxygenated volatile organic compounds (OVOCs). More precisely, literature findings suggest that compounds such as isoprene (ISP), the highest emitted biogenic volatile organic compound (BVOC) in the atmosphere, could be involved in heterogeneous processes on atmospheric particles and could account for OVOC formation. Hence, within this framework, the adsorption of ISP on Gobi dust was investigated in the temperature (T) and relative humidity (RH) ranges of 253–358 K and <0.01–10%, respectively, using zero air as the bath gas. The kinetic measurements were performed using a novel experimental setup equipped with a selected-ion flow-tube mass spectrometer (SIFT-MS) for gas-phase monitoring. The initial uptake coefficient, γ0, of ISP was measured as a function of several parameters (ISP mass, temperature, and RH). γ0 is evidenced as inversely dependent upon the RH and dependent upon the temperature according to the empirical equations γ0 = 2.7 × 10–10/(0.005 + RH1.44) and γ0 = (5.30 ± 1.5) × 10–7 exp[(1376 ± 133)/T], respectively. Furthermore, adsorption isotherms of ISP were determined, and the results were simulated with the Langmuir adsorption model to obtain the partitioning constant, K Lin, as a function of the RH and temperature according to the equations K Lin (296 K) = 0.028/(0.604 + RH1.54) and K Lin = (1.392 ± 0.33) × 10–7 exp[(3732 ± 140)/T], respectively. The effect of an increasing temperature on the reversible fraction of ISP adsorption on Gobi dust was recorded. The atmospheric lifetime of the heterogeneous loss of ISP onto Gobi dust was calculated for forested environments and found to be several years.