An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

Abstract

Abstract. Nanoparticles of iron oxide (crystalline and amorphous), silicon oxide and magnesium oxide were investigated for their propensity to nucleate ice over the temperature range 180-250 K, using the AIDA chamber in Karlsruhe, Germany.All samples were observed to initiate ice formation via the deposition mode at threshold ice super-saturations (RHi thresh ) ranging from 105% to 140% for temperatures below 220 K. Approximately 10% of amorphous Fe 2 O 3 particles (modal diameter = 30 nm) generated in situ from a photochemical aerosol reactor, led to ice nucleation at RHi thresh = 140% at an initial chamber temperature of 182 K. Quantitative analysis using a singular hypothesis treatment provided a fitted function [n s (190K) = 10 (3.33×s ice )+8.16 ] for the variation in ice-active surface site density (n s :m −2 ) with ice saturation (s ice ) for Fe 2 O 3 nanoparticles. This was implemented in an aerosol-cloud model to determine a predicted deposition (mass accommodation) coefficient for water vapour on ice of 0.1 at temperatures appropriate for the upper atmosphere. Classical nucleation theory was used to determine representative contact angles (θ) for the different particle compositions. For the in situ generated Fe 2 O 3 particles, a slight inverse temperature dependence was observed with θ = 10.5 • at 182 K, decreasing to 9.0 • at 200 K (compared with 10.2 • and 11.4 • respectively for the SiO 2 and MgO particle samples at the higher temperature).These observations indicate that such refractory nanoparticles are relatively efficient materials for the nucleation of ice under the conditions studied in the chamber which correspond to cirrus cloud formation in the upper troposphere. The results also show that Fe 2 O 3 particles do not act as Correspondence to: J. M. C. Plane (j.m.c.plane@leeds.ac.uk) ice nuclei under conditions pertinent for tropospheric mixed phase clouds, which necessarily form above ∼233 K. At the lower temperatures (<150 K) where noctilucent clouds form during summer months in the high latitude mesosphere, higher contact angles would be expected, which may reduce the effectiveness of these particles as ice nuclei in this part of the atmosphere.

Prognostic Value of Cardiovascular Magnetic Resonance and Single-Photon Emission Computed Tomography in Suspected Coronary Heart Disease: Long-Term Follow-up of a Prospective, Diagnostic Accuracy Cohort Study

“…properties and ice nucleating ability (Saunders, et al, 2010, Saunders andPlane, 2006). We 601 note that the amorphous nature found for those particles is similar to that described here.…”

Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures

“…This is similar to the volume based cumulative nucleus spectrum defined by Vali (1971Vali ( , 1994. The ice active surface site density has been applied to a number of other experimental studies of different deposition ice nuclei (Connolly et al, 2009;Saunders et al, 2010;Steinke et al, 2011;Niemand et al, 2012). It is a particularly useful quantity as it provides a surface area independent measurement of a materials ability to nucleate ice.…”

“…11. Arizona Test Dust (ATD, grey triangles) (Connolly et al, 2009), volcanic ash from the Eyjafjallajökull eruption (grey circles) (Steinke et al, 2011) and iron oxide nanoparticles (dashed grey line) (Saunders et al, 2010) have higher n s values and are therefore more efficient ice nuclei than glassy aerosol per unit of surface area. While mineral dust is clearly a more effective ice nucleus, the number density (and therefore surface area) of aerosol particles which are potentially glassy far exceeds that of mineral dust in the upper troposphere (Froyd et al, 2010).…”

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

“…Such studies became feasible after the installation of the new laser scattering and depolarisation setup SIMONE 1 at the chamber in 2006. SIMONE has been successfully employed in several AIDA campaigns on the homogeneous and heterogeneous nucleation of ice particles (Wagner et al, 2007;Saunders et al, 2010;Steinke et al, 2011), in studies on the depolarisation characteristics of ice clouds generated under defined temperature and humidity conditions (Amsler et al, 2009;Schön et al, 2011;Abdelmonem et al, 2011), as well as for probing phase transitions in inorganic and organic aerosols .…”