Water Interaction with Mineral Dust Aerosol: Particle Size and Hygroscopic Properties of Dust

• Published in: ACS earth and space chemistry Vol. 2; no. 4; pp. 376 - 386
• Main Authors: Ibrahim, Sara, Romanias, Manolis N, Alleman, Laurent Y, Zeineddine, Mohamad N, Angeli, Giasemi K, Trikalitis, Pantelis N, Thevenet, Frederic
• Format: Journal Article
• Language: English
• Published: American Chemical Society 19.04.2018; ACS
• Subjects: Chemical Sciences; Environmental Sciences; Global Changes; or physical chemistry; Theoretical and; BET theory; desorption kinetics; adsorption isotherms; water adsorption; DRIFT spectroscopy
• ISSN: 2472-3452; 2472-3452
• DOI: 10.1021/acsearthspacechem.7b00152

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). N2 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 ± 1, 17 ± 1, 22 ± 2, 25 ± 2, and 28 ± 2% RH for ATD of 0–3, 5–10, 10–20, 20–40, and 40–80 μm, respectively. Additional water layers are formed at higher RH conditions. Thorough comparisons point that smaller particles adsorb water more efficiently. To better assess the impact of size on water uptake, for the first time, the desorption kinetics of water are determined. It is found that water desorption follows second-order kinetics, and results are fitted to determine the desorption rate coefficients for each dust grade. As a conclusion, results provide evidence that the size distribution is a key factor influencing water uptake onto mineral dust that could impact mineral particle scattering ability, adsorption, and photoreactivity properties.