Freezing temperatures of H2SO4/HNO3/H2O mixtures: Implications for polar stratospheric clouds

Song, Naihui

doi:10.1029/94gl02459

Cited by 31 publications

(20 citation statements)

References 14 publications

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“…Nevertheless, explanations for NAT formation processes above T ICE have also been invoked, such as formation of amorphous solid particles at temperatures above T ICE (type 1c PSC) and subsequent cystallization upon warming [ Tabazadeh and Toon , 1996]; or direct NAT formation on STS solutions either when strong mesoscale temperature fluctuations lead the droplet composition close to the stoichiometry of NAT [ Meilinger et al , 1995; Song , 1994] or when temperature dwells long enough inside a well‐defined “nucleation window” [ Tabazadeh et al , 2001]. There is also a suggestion for heterogeneous freezing in the presence of suitable freezing nuclei [ Drdla et al , 2002].…”

Section: Microphysical Simulationsmentioning

confidence: 99%

Polar stratospheric clouds observed during the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign

et al. 2004

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In this work, observations of polar stratospheric clouds (PSC) carried out during one flight of the stratospheric research aircraft Geophysica deployed in the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign in September–October 1999 are presented. An analysis of data from the two lidars and a backscatter sonde on board the Geophysica aircraft is presented, coupled with temperature measurements. The observations are analyzed with the aid of a mesoscale model to provide air mass thermal histories and a microphysical box model to simulate PSC formation. The results obtained from this comparison are discussed in view of the theories for PSC formation processes.

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Section: Microphysical Simulationsmentioning

confidence: 99%

Polar stratospheric clouds observed during the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign

et al. 2004

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“…Whether this occurs under stratospheric conditions is uncertain. Some studies have concluded that the HNO 3 content does promote freezing [ Molina et al , 1993; Beyer et al , 1994; Song , 1994; Iraci et al , 1995; Bertram and Sloan , 1998a, 1998b; Salcedo et al , 2001] but others have found no freezing until below the ice frost point [ Koop et al , 1995, 2000].…”

Section: Introductionmentioning

confidence: 99%

Microphysical modeling of the 1999–2000 Arctic winter: 1. Polar stratospheric clouds, denitrification, and dehydration

2002

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The freezing processes that may lead to the formation of solid phase polar stratospheric clouds (PSCs) have been examined to assess their winter‐long effects, especially denitrification, in a coupled microphysical/photochemical model. Trajectory simulations spanned from November 1999 to April 2000, using a large set of trajectories which provided representative coverage of the entire Arctic vortex through the period of PSC formation and ozone depletion. A freezing process occurring at temperatures above the ice frost point is shown to be necessary to explain both the occurrence of solid phase PSCs early in the winter and denitrification, especially without dehydration. If freezing only occurs below the ice frost point the primary contributor to denitrification is actually sedimentation of liquid phase PSC particles. The mechanism of a second freezing process, occurring above the ice frost point, can not yet be conclusively determined. Of the cases considered, heterogeneous freezing of the aerosol to form nitric acid trihydrate (NAT) particles best reproduced solid phase PSC formation and observations of widespread denitrification with limited dehydration. The simulations constrain the number of frozen particles to be near either 0.02% or 1% of the total aerosol number; values in between 0.02% and 1% produce more intense denitrification than observed, demonstrating that small changes in the number of frozen particles could exacerbate denitrification. However, this result was contingent upon assuming that the heterogeneous nuclei remain active, producing PSCs, throughout the winter. An idealized homogeneous freezing process was also able to produce NAT PSCs and denitrification (rates of 106–107 cm−3 s−1 compared favorably with data) but differed from observations in one key aspect: denitrification was more frequently accompanied by dehydration. Nitric acid dihydrate (NAD) particles were less effective than NAT at denitrification, but heterogeneous freezing of 0.1% of the aerosol yielded results marginally consistent with measurements. An important limitation, however, of all the scenarios considered is that they produced more intense and more widespread dehydration than was observed. This suggests that model minimum temperatures (from UK Meteorological Office analyses) were too cold by 1 to 3 K.

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“…Stratospheric sulfate aerosols (SSAs) affect the composition of the upper atmosphere through heterogeneous chemical reactions, as well as serving as nucleation sites for polar stratospheric clouds, or PSCs [Tolbert, 1994]. Recently, significant research has been aimed at answering pressing questions concerning the microphysics of PSCs and their precursors, SSAs [Turco and Hamill, 1992;Luo et al, 1992; van Doren et al, 1991; Watson et al, 1990;Dye et al, 1992;Anthony et al, 1995;Larsen, 1994;Beyer et al, 1994;Song, 1994;Tabazadeh and Toon, 1995;Luo et al, 1994;Jensen et al, 1991;Koop et al, 1995]. Several studies have attempted to determine freezing points for bulk sulfuric acid/water solutions, since the physical state of the aerosol will no doubt affect both the rate of heterogeneous reactions and the process of PSC formation.…”

Section: Introductionmentioning

confidence: 99%

Infrared spectroscopy of sulfuric acid/water aerosols: Freezing characteristics

Clapp¹,

Niedziela²,

Richwine³

et al. 1997

J. Geophys. Res.

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Abstract. A low-temperature flow cell has been used in conjunction with a Fourier transform infrared (FT-IR) spectrometer to study sulfuric acid/water aerosols. The aerosols were generated with a wide range of composition (28 to 85 wt %), including those characteristic of stratospheric sulfate aerosols, and studied over the temperature range from 240 K to 160 K. The particles exhibited deep supercooling, by as much as 100 K below the freezing point in some cases. Freezing of water ice was observed in the more dilute (<40 wt % sulfuric acid) particles, in agreement with the predictions of Jensen et al. and recent observations by Bertram et al. In contrast with theoretical predictions, however, the entire particle often does not immediately freeze, at least on the timescale of the present experiments (seconds to minutes). Freezing of the entire particle is observed at lower temperatures, well below that characteristic of the polar stratosphere.

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Freezing temperatures of H₂SO₄/HNO₃/H₂O mixtures: Implications for polar stratospheric clouds

Cited by 31 publications

References 14 publications

Polar stratospheric clouds observed during the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign

Polar stratospheric clouds observed during the Airborne Polar Experiment–Geophysica Aircraft in Antarctica (APE‐GAIA) campaign

Microphysical modeling of the 1999–2000 Arctic winter: 1. Polar stratospheric clouds, denitrification, and dehydration

Infrared spectroscopy of sulfuric acid/water aerosols: Freezing characteristics

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