New cloud chamber experiments on the heterogeneous ice nucleation ability of oxalic acid in the immersion mode

Abstract

Abstract. The heterogeneous ice nucleation ability of oxalic acid in the immersion mode has been investigated by controlled expansion cooling runs with airborne, ternary solution droplets composed of, (i), sodium chloride, oxalic acid, and water (NaCl/OA/H 2 O) and, (ii), sulphuric acid, oxalic acid, and water (H 2 SO 4 /OA/H 2 O). Polydisperse aerosol populations with median diameters ranging from 0.5-0.7 µm and varying solute concentrations were prepared. The expansion experiments were conducted in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at initial temperatures of 244 and 235 K. In the ternary NaCl/OA/H 2 O system, solid inclusions of oxalic acid, presumably nucleated as oxalic acid dihydrate, were formed by temporarily exposing the ternary solution droplets to a relative humidity below the efflorescence point of NaCl. The matrix of the crystallised NaCl particulates triggered the precipitation of the organic crystals which later remained as solid inclusions in the solution droplets when the relative humidity was subsequently raised above the deliquescence point of NaCl. The embedded oxalic acid crystals reduced the critical ice saturation ratio required for the homogeneous freezing of pure NaCl/H 2 O solution droplets at a temperature of around 231 K from 1.38 to about 1.32. Aqueous solution droplets with OA inclusions larger than about 0.27 µm in diameter efficiently nucleated ice by condensation freezing when they were activated to micron-sized cloud droplets at 241 K, i.e., they froze well above the homogeneous freezing temperature of pure water droplets of about 237 K. Our results on the immersion freezing potential of oxalic acid corroborate the findings from a recent study with emulsified aqueous solutions containing crystalline oxalic acid. In those experiments, the crystallisation of oxalic acid diyhdrate was triggered by a preceding homogeneous freezing Correspondence to: R. Wagner (robert.wagner2@kit.edu) cycle with the emulsion samples. The expansion cooling cycles with ternary H 2 SO 4 /OA/H 2 O solution droplets were aimed to analyse whether those findings can be transferred to ice nucleation experiments with airborne oxalic acid containing aerosol particles. Under our experimental conditions, the efficiency by which the surface of homogeneously nucleated ice crystals triggered the precipitation of oxalic acid dihydrate was very low, i.e., less than one out of a hundred ice crystals that were formed by homogeneous freezing in a first expansion cooling cycle left behind an ice-active organic crystal that acted as immersion freezing nucleus in a second expansion cooling cycle.

Temperature-dependent formation of NaCl dihydrate in levitated NaCl and sea salt aerosol particles

“…Wagner et al observed a similar effect in crystallization of ternary solution droplets composed of oxalic acid, NaCl, and water in the AIDA cloud chamber at 244 K. 69 There, the crystallization of NaCl dihydrate was facilitated by the presence of oxalic acid crystals. Recently, the CaSO 4 was identified by means of EDX analysis of the sea salt particles collected in the field.…”

Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals – cloud chamber measurements in the context of contrail and cirrus microphysics

“…A detailed description of the chamber preparation, the chamber instrumentation, and the expansion cooling technique for ice cloud studies is given in the recent papers by Wagner et al (2010Wagner et al ( , 2011. In the following, we therefore only give a brief introduction to the chamber and its intrumentation.…”

A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques

“…To determine the purity of our sample, and to compare this with previous observations, the dust mineralogy of a bulk illite NX sample was characterized using XRD (Waseda et al, 2011) prior to distribution. In addition, complementary energy dispersive X-ray (EDX) spectroscopy analysis was performed to characterize the elemental composition of in-dividual particles.…”

“…The same disperser type was used at both chambers for particle generation, and the upstream cyclone impactors (D 50 ∼ 1 and 2.5 µm) were similarly deployed to filter out any larger particles and safeguard against injecting these particles into the vessel. We note that a linear correction factor of ∼ 2 was applied to convert the optical diameter measured by the welas-OPC to the APS-inferred volume equivalent di-ameter in several studies (Wagner et al, 2011;Hiranuma et al, 2014a).…”