Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

Abstract

Abstract. During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona Test Dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed particles' heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at −30 • C and −25 • C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 • C -intended to evaporate the sulphuric acid coating -reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles Correspondence to: R. C. Sullivan (rsullivan@atmos.colostate.edu) compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability under both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

Evolution of particle composition in CLOUD nucleation experiments

“…As we can see, the hygroscopicities for the inorganic compounds (SA, AbS, AS) in Table 2 are substantially higher than the ones for organic species. It should be noted that there are two reported kappa vales for SA particles (0.7 and 0.9: Sullivan et al, 2010;Petters and Kreidenweis, 2007). When the theoretical SA kappa value is reduced by the effect of the residual water in the dry particles in HTDMA measurements the value is close to 0.7.…”

“…Biskos et al (2009) also reported the reduced hygroscopic properties for the SAparticles smaller than 36.1 nm based on partial neutralisation because of contaminant NH 3 in the experimental HTDMA set-up. Hence, we use the value 0.7 for the kappa value of SA particles (Sullivan et al, 2010). With known O:C ratio the organic hygroscopicity (κ o ) can be explicit from previous measurements by Massoli et al, 2010 (e.g. at O:C 0.1 it is 0.05).…”

“…The theoretical hygroscopic growth factors and hygroscopicities for sulphuric acid (SA), ammonium sulphate (AS) and ammonium bisulphate (AbS) were derived based on experiments (Joutsensaari et al, 2001(Joutsensaari et al, , 2004Hämeri et al, 2000;Vehkamäki et al, 2002) and model results reported elsewhere (Topping et al, 2005). The theoretical ethanol growth factors and affinities were derived based on methods and experiments reported by Joutsensaari et al (2001) and Vaattovaara et al (2005).…”

Different contact angle distributions for heterogeneous ice nucleation in the Community Atmospheric Model version 5

“…ATD can possibly be more ice nucleation active than natural desert dust, either due to its enhanced roughness resulting from milling or due to its different mineralogical composition . Another reason for lower activity of natural dust particles is related to their aging processes in the atmosphere, which may reduce their ice nucleation ability (Sullivan et al, 2010).…”

Single Particle Measurements of the Optical Properties of Small Ice Crystals and Heterogeneous Ice Nuclei

“…That study also demonstrated that due to the differences in scattering, each of the 13 dust types measured could be grouped according to their individual optical properties. In addition, mineral dusts facilitate the nucleation of ice by acting as heterogeneous ice nuclei (DeMott et al 2003;Archuleta et al 2005;Fornea et al 2009;Sullivan et al 2010;Murray et al 2012). …”