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The study of finely divided aqueous systems as a clue to understanding the formation mechanisms of polar stratospheric clouds:1. HNO3/H2O and H2SO4/H2O systems.

Bogdan, A. and Kulmala, M. and MacKenzie, A. Robert and Laaksonen, A. and Molina, M. J. and Avramenko, A. (2003) The study of finely divided aqueous systems as a clue to understanding the formation mechanisms of polar stratospheric clouds:1. HNO3/H2O and H2SO4/H2O systems. Journal of Geophysical Research: Atmospheres, 108 (D10). p. 4302. ISSN 0747-7309

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Abstract

The study of nanometer-scale aqueous systems (finely divided aqueous systems (FDAS)) can be achieved using the absorption of vapors on fumed silica (SiO2) powder. Being a product of flame synthesis technology, fumed silica particles (6–11 nm) can be considered to be analogous to the silica smoke particles of anthropogenic and extraterrestrial origin that are supposed to be widely present in the stratosphere and mesosphere. Here, we describe the freezing and melting behavior of nanometer-scale pure H2O and binary HNO3/H2O and H2SO4/H2O systems of varying acid content, using differential scanning calorimetry (DSC). Besides reductions of melting temperature, T m , large reductions in freezing and melting enthalpies, with ΔH f < ΔH m , in comparison with bulk solutions have also been detected. Experiments showed that fumed silica can serve as a freezing nucleus for heterogeneous ice nucleation from dilute HNO3/H2O droplets. The onset of freezing of a silica/HNO3/H2O sample with HNO3/H2O stoichiometry close to that of NAT (53 ± 5 wt % HNO3) at temperatures ≈7 K warmer than the ice frost point suggests that silica particles can promote heterogeneous freezing of nitric acid hydrates in the stratosphere. Freezing of bulk droplets (53.2 wt % HNO3) supported on Al substrate at temperatures warmer than −73°C (200 K) suggests that in principle, Al2O3 surface may induce freezing of HNO3 hydrates as well. DSC measurements performed on the silica/H2SO4/H2O nanosystem showed that at stratospheric temperatures, silica particles cannot induce heterogeneous formation of sulfuric acid hydrates.

Item Type: Article
Journal or Publication Title: Journal of Geophysical Research: Atmospheres
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Departments: Faculty of Science and Technology > Lancaster Environment Centre
ID Code: 21374
Deposited By: ep_ss_importer
Deposited On: 12 Jan 2009 14:58
Refereed?: Yes
Published?: Published
Last Modified: 17 Sep 2013 08:17
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/21374

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