Adsorbed water on the surface of atmospheric mineral dust has recently been shown to significantly affect the ability of mineral dust aerosol to act as cloud condensation nuclei. We have studied water adsorption as a function of relative humidity (RH) on goethite (α-FeO(OH)), a common component of atmospheric mineral dust. The goethite surface area and particle size was determined using BET analysis and with N2 as an adsorbate and scanning electron microscopy, respectively. Water adsorption on the sample was monitored using horizontal attenuated total reflectance Fourier transform infrared (HATR-FTIR) spectroscopy equipped with a flow cell. Water content was determined using Beer’s law and the optical constants for bulk water. The results were analyzed using Type II adsorption isotherms to model multilayer adsorption, including BET (Brunauer, Emmet and Teller) and FHH (Frenkel, Halsey and Hill). BET fits to experimental data provide parameters of monolayer coverage, while the FHH provides insight into multilayer adsorption mechanisms. Results indicate that goethite contains 5% H2O by mass at ~50% RH, which increases to 12% by mass at ~90% RH. FHH adsorption parameters are used in FHH Activation Theory (FHH-AT) to predict goethite cloud condensation cuclei (CCN) activation. Experimental water adsorption results, theoretical adsorption parameters, and CCN activity for goethite aerosol will be presented.

Water adsorption on goethite: CCN activation from Frenkel, Halsey and Hill activation theory

253rd National Meeting (2017)

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