Jack Jie Lin , Kamal Raj R, Stella Wang, Esko Kokkonen, Mikko-Heikki Mikkelä, Samuli Urpelainen, Nønne L. Prisle

In this work we study the adsorption, or uptake, of water onto deposited inorganic sodium chloride and organic malonic acid and sucrose nanoparticles at low relative humidities from 0 to 16%. We employ the surface sensitive ambient pressure x-ray photoelectron spectroscopy technique, which has a detection sensitivity from parts per thousand. Our results show that water is adsorbed on sodium chloride aerosols already well below deliquescence at low relative humidities, and that the chemical environment on the aerosol surface is changing with increasing humidity. While the sucrose aerosols exhibit only very modest changes on the surface at these relative humidites, the chemical composition and environment of malonic acid aerosol surfaces is clearly affected. Our observations indicate that the water uptake by inorganic and organic aerosols at low relative humidities could already have an impact on atmospheric chemistry. We also conclude that the ambient pressure x-ray photoelectron spectroscopy is indeed a viable tool for studying changes in particular on the surfaces of atmospherically relevant aerosols at low relative humidities.