The unsuitability of meteoritic and other nuclei for polar stratospheric cloud freezing

Abstract

Bulk freezing experiments have been performed with binary and ternary HNO3/H2SO4/H2O solutions containing original micrometeorites, ground samples of representative larger meteorites and other freezing nuclei of potential stratospheric importance. The experiments enable us to determine upper bounds for the heterogeneous freezing rates of sulfuric and nitric acid hydrates. Based on an analysis of the meteoritic mass flux from space and of the modifications meteorites undergo when entering the atmosphere, the resulting morphology and surface area of extraterrestrial material in the stratosphere are estimated. From this micrometeorites gained from Antarctica are shown to be a good proxy for meteoritic surfaces in the stratosphere. In combination with this analysis the freezing experiments suggest that heterogeneous nucleation rates on micrometeorites are too low to enhance freezing of polar stratospheric clouds above the frost point.

Nitric Acid Trihydrate (NAT) formation at low NAT supersaturation in Polar Stratospheric Clouds (PSCs)

“…Further, heterogeneous nucleation of ternary solutions on micrometeorites has been investigated calorimetrically by Biermann et al (1996). They found that the presence of meteoritic material accelerates the freezing of supercooled ternary solutions.…”

“…A NAT nucleation rate of similar magnitude (1.15×10 −5 cm −3 air h −1 ) has been derived from MLS observations in the winters 1994/1995, 1996/1997(Davies et al, 2005. A factor of 4 lower NAT nucleation rate has been determined from ER-2 measurements in the Arctic winter 1999/2000 (Fahey et al, 2001;Carslaw et al, 2002).…”

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

“…614 Biermann, et al (1996), who used micrometeorites as analogues for MSP nucleating 615 crystallisation in polar stratospheric clouds, found that nucleation rates were not high 616 enough to explain observed cloud. As the authors in that study observed, micrometeorites 617 are generally compact, dense particles coated with magnetite crystals.…”

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

“…Whilst deposition nucleation studies, with regard to the lower atmosphere, for materials of terrestrial origin such as mineral dusts (Archuleta et al, 2005;Möhler et al, 2006) and soot (Dymarska et al, 2006;Kärcher et al, 2007) are of great current interest, only the experimental study of Bigg and Giutronich (1967) seems to have considered the activating role of recondensed meteoric material in the atmosphere, and only then with respect to the troposphere. Other attempts to investigate the freezing capacity of meteoritic material, such as that of Biermann et al (1996) with regard to acid-water solutions in the stratosphere, have reported a largely negative (inactive) potential, but the samples used (whole or ground micrometeorites) are unlikely to be representative of the composition and morphology of recondensed (smoke) particles, and consequently exhibit the appropriate particle surface and nucleation properties. This point was argued by Bigg and Giutronich (1967) with respect to earlier cited nucleation studies.…”