Freezing points of H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;
                        aqueous solutions and formation of stratospheric ice clouds

Ohtake, Takeshi

doi:10.3402/tellusb.v45i2.15588

Cited by 32 publications

(19 citation statements)

References 12 publications

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“…The extensive supercooling for 60-75 wt % H2SO 4 is consistent with that reported previously [Middlebrook et al, 1993;Ohtake, 1993;Zhang et al, 1993;Beyer et al, 1994;Song, 1994]. Freezing points of more concentrated sulfuric acid (>75 wt %) have been investigated by Ohtake [1993] and Song [1994], using bulk solutions.…”

Section: Freezing Point Measurementssupporting

confidence: 88%

“…Also, theoretical predictions of freezing points of sulfate aerosols at stratospheric conditions are severely limited by the lack of fundamental physical parameters concerning surface energies of various sulfuric acid hydrates [Jenson et al, 1991;Luo et al, 1992]. Recently, a number of studies have investigated freezing points of liquid sulfuric acid using bulk solutions [Middlebrook et al, 1993;Ohtake, 1993;Zhang et al, 1993;Beyer et al, 1994;Song, 1994]. Many of the studies dealt with rather dilute sulfuric acid in order to elucidate the role of sulfate aerosols in PSC nucleation.…”

Section: Introductionmentioning

confidence: 99%

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Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

Zhang¹,

Leu²,

Keyser³

1995

J. Geophys. Res.

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We have investigated some thermodynamic properties (i.e., freezing/melting points) and heterogeneous chemistry of sulfuric acid monohydrate (SAM, H2SO4 · H2O), using a fast flow reactor coupled to a quadrupole mass spectrometer. The freezing point observations of thin liquid sulfuric acid films show that for acid contents between 75 and 85 wt % the monohydrate crystallizes readily at temperatures between 220 and 240 K on a glass substrate. Once formed, SAM can be thermodynamically stable in the H2O partial pressure range of (1–4)×10−4 torr and in the temperature range of 220–240 K. For a constant H2O partial pressure, lowering the temperature causes SAM to melt when the temperature and water partial pressure conditions are out of its stability regime. The reaction probability measurements indicate that the hydrolysis of N2O5 is significantly suppressed owing to the formation of crystalline SAM: The reaction probability on water‐rich SAM (with higher relative humidity, or RH) is of the order of 10−3 at 210 K and decreases by more than an order of magnitude for the acid‐rich form (with lower RH). The hydrolysis rate of ClONO2 on water‐rich SAM is even smaller, of the order of 10−4 at 195 K. These reported values on crystalline SAM are much smaller than those on liquid solutions. No enhancement of these reactions is observed in the presence of HCl vapor at the stratospheric concentrations. In addition, Brunauer, Emmett, and Teller analysis of gas adsorption isotherms and photomicrography have been performed to characterize the surface roughness and porosities of the SAM substrate. The results suggest the possible formation of SAM in some regions of the middle‐ or low‐latitude stratosphere and, consequently, much slower heterogeneous reactions on the frozen aerosols.

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Section: Freezing Point Measurementssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

Zhang¹,

Leu²,

Keyser³

1995

J. Geophys. Res.

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“…Freezing points were found to be reproducible within a few degrees. For the sulfuric acid and water system, the current data reproduce reasonably well those reported by Song and Williams (1993) and Ohtake (1993). For a particular test tube in a freezing batch, nitric acid was observed to change its freezing point.…”

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confidence: 88%

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

Song

1994

Geophysical Research Letters

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The freezing temperatures of H2SO4/HNO3/H2O mixtures were systematically documented. Nitric acid was found to affect freezing significantly. Measurements show that nitric acid can cause substantial supercooling over a broad composition range. However, some ternary compositions, like to those in polar stratospheric clouds (PSCs), have high freezing temperatures. The freezing of PSC particles could be controlled by the temperature and vapor pressure of both nitric acid and water in a non‐linear way. Formation of polar stratospheric clouds may be forecasted on the basis of conditions of temperature and vapor contents of water and nitric acid.

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“…This apparently confusing behaviour can be attributed to the formation of ice frost or NAT on the containment walls from the vapour phase. Ohtake [1993] also reported frequent observations of frost formation on the walls of the glass tubes, in particular when the tubes were not well-sealed, and speculated whether this could influence the freezing process. But even when using well-sealed glass tubes we observed that, during rapid cooling, parts of the water vapour above the liquid did not condense into the liquid itself, but as water ice on the glass walls.…”

Section: Paper Number 95gl00814mentioning

confidence: 98%

Do stratospheric aerosol droplets freeze above the ice frost point?

Koop

Biermann

Raber

et al. 1995

Geophysical Research Letters

159

150

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Laboratory experiments are presented which show that liquid stratospheric aerosol droplets under polar winter conditions do not freeze for temperatures higher than the water ice saturation temperature (frost point). Calorimetric measurements of the freezing of supercooled H2SO4/HNO3/H2O bulk solutions with concentrations typical of the polar stratospheric aerosol exhibit very small freezing rates, which excludes the possibility of homogeneous freezing of the droplets for temperatures above the frost point. Even heterogeneous formation of H2SO4 and HNO3 hydrates at these temperatures is a very inefficient process unless the stratosphere offers nuclei better suited for nucleation than those present in the laboratory experiments, which appears to be unlikely. Only ice was found to be a potential nucleus suited for the formation of the hydrates, which could cause the hydrates to freeze at temperatures below the frost point.

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Freezing points of H<sub>2</sub>SO<sub>4</sub> aqueous solutions and formation of stratospheric ice clouds

Cited by 32 publications

References 12 publications

Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

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

Do stratospheric aerosol droplets freeze above the ice frost point?

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Freezing points of H<sub>2</sub>SO<sub>4</sub> aqueous solutions and formation of stratospheric ice clouds

Cited by 32 publications

References 12 publications

Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

Sulfuric acid monohydrate: Formation and heterogeneous chemistry in the stratosphere

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

Do stratospheric aerosol droplets freeze above the ice frost point?

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Product

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