Pre-deliquescent water uptake in deposited nanoparticles observed with in situ ambient pressure X-ray photoelectron spectroscopy

Abstract

<jats:p>Abstract. We study the adsorption of water onto deposited inorganic sodium chloride and organic malonic acid and sucrose nanoparticles at ambient water pressures corresponding to relative humidities (RH) from 0 to 16 %. To obtain information about water uptake at conditions where not accessible with typical aerosol instrumentation, we use surface-sensitive ambient pressure X-ray photoelectron spectroscopy (APXPS), which has a detection sensitivity from parts per thousand. Our results show that water is already adsorbed on sodium chloride particles at RH well below deliquescence, and that the chemical environment on the particle surface is changing with increasing humidity. While the sucrose particles exhibit only very modest changes on the surface at these relative humidities, the chemical composition and environment of malonic acid particle surfaces is clearly affected. Our observations indicate that water uptake by inorganic and organic aerosol particles could already have an impact on atmospheric chemistry at low relative humidities. We also conclude that the APXPS technique is a viable tool for studying chemical changes on the surfaces of atmospherically relevant aerosol particles which are not accessible with typical online mass- and volume-based methods. </jats:p>

The effect of relative humidity on CaCl2 nanoparticles studied by soft X-ray absorption spectroscopy

“…It has been applied to a variety of non-supported microparticles and NPs, such as electrodynamically trapped SiO 2 , 22 Au-coated SiO 2 , 23 levitating droplets, 24 in situ generated soot, 25 and atomized salt solutions. 26,27 Compared to X-ray-based photoelectron and photoabsorption spectroscopies nowadays available also with RH control for deposited nanoparticles 28 and salt surfaces, 29 using a continuously renewed nanoparticle beam we ensure that there are no substrate effects, radiation induced changes, and no further growth or change of particles aer deposition. Here we apply XAS to study the hydration state of CaCl 2 -NPs by comparing XAS spectra of NPs generated at different RH to those obtained from water in different states, aqueous CaCl 2 solution, and solid CaCl 2 .…”

Upgrade of the SPECIES beamline at the MAX IV Laboratory

“…The same cooling channel can also be used to cool the samples below RT, by flowing a cold gas or liquid through the channel. So far it has been demonstrated that by flowing cold nitrogen gas through the channel it is possible to cool the samples down to À30 C. Cooling the samples further extends the available sample environments and is useful, for instance, in the cases where controlling the relative humidity inside the cell is desired (Lin et al, 2021). The same cooling could also be used for the investigations of ice on surfaces.…”