Homogeneous Freezing of Concentrated Aqueous Nitric Acid Solutions at Polar Stratospheric Temperatures

Salcedo, D.; Molina, Luisa T.; Molina, Mario J.

doi:10.1021/jp001639s

Cited by 77 publications

(235 citation statements)

References 33 publications

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“…We have applied the surface nucleation mechanism of Tabazadeh et al (2002) because this, to our knowledge, is the latest published available parameterisation of hydrate nucleation out of STS working at temperature above the ice frost point. Secondly, the surface nucleation seems more consistent with laboratory experiments (Tabazadeh et al, 2002), compared to a corresponding volume nucleation parameterisation (Tabazadeh et al, 2001;Salcedo et al, 2001). However, we have also made simulations with the latter volume-proportional nucleation and could obtain equally good agreement with the observations if these nucleation rates were increased by a factor 10.…”

Section: Discussionsupporting

confidence: 77%

Formation of solid particles in synoptic-scale Arctic PSCs in early winter 2002/2003

et al. 2004

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Abstract. Polar stratospheric clouds (PSC) have been observed in early winter (December 2002) during the SOLVE II/Vintersol campaign, both from balloons carrying comprehensive instrumentation for measurements of chemical composition, size distributions, and optical properties of the particles, as well as from individual backscatter soundings from Esrange and Sodankylä. The observations are unique in the sense that the PSC particles seem to have formed in the early winter under synoptic temperature conditions and not being influenced by mountain lee waves. A sequence of measurements during a 5-days period shows a gradual change between liquid and solid type PSCs with the development of a well-known sandwich structure. It appears that all PSC observations show the presence of a background population of solid particles, occasionally mixed in with more optically dominating liquid particles. The measurements have been compared with results from a detailed microphysical and optical simulation of the formation processes. Calculated extinctions are in good agreement with SAGE-III measurements from the same period. Apparently the solid particles are controlled by the synoptic temperature history while the presence of liquid particles is controlled by the local temperatures at the time of observation. The temperature histories indicate that the solid particles are nucleated above the ice frost point, and a surface freezing mechanism for this is included in the model. Reducing the calculated freezing ratesCorrespondence to: N. Larsen (nl@dmi.dk) by a factor 10-20, the model is able to simulate the observed particle size distributions and reproduce observed HNO 3 gas phase concentrations.

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Section: Discussionsupporting

confidence: 77%

Formation of solid particles in synoptic-scale Arctic PSCs in early winter 2002/2003

et al. 2004

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“…They found that surface-based rate expressions are consistent with all the considered laboratory data [44]- [48] and that the homogeneous nucleation process occurring in atmospheric droplets may be a surface-rather than a volume-related rate process. The authors concluded that the rates of ice nucleation in droplets in air are higher than those observed in oil, and that surface nucleation is favoured over volume nucleation when supercooled water drops are smaller and temperature higher.…”

Section: Reported Datasupporting

confidence: 56%

Does the Homogeneous Ice Nucleation Initiate in the Bulk Volume or at the Surface of Super-Cooled Water Droplets? A Review

Santachiara¹,

Belosi²

2014

ACS

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The formation of ice in clouds can occur through primary processes, either homogeneously or heterogeneously triggered by aerosol particles called ice nuclei, as well as through secondary processes. The homogeneous ice nucleation process involves only pure water or solution droplets. Homogeneous freezing is crucial for the microphysics in the formation of high-altitude cirrus and polar stratospheric clouds, and also in the glaciation of thunderclouds, at temperatures below about 235 K. Nucleation rates in supercooled water have been measured using different experimental techniques: expansion cloud chambers, water-in-oil emulsions, levitation methods, free falling droplets, supersonic nozzles, field measurements, and molecular dynamics simulations. An important question concerns the possibility that the nucleation process in supercooled water can occur not only in the interior volume of the droplet, but even at or close to its surface. Even if there is no conclusive evidence, the majority of experimental and theoretical results suggest that the contribution of surface nucleation increases with decreasing radius of the supercooled droplets, and the surface (or sub-surface) nucleation rate is prevalent for droplets with radius lower than about 5 μm. If homogeneous freezing initiates at the droplet surface, the freezing rate should depend on the droplet size, and even a slight contamination by molecules within the surface layer could hamper the rate of the nucleation process.

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“…Homogeneous nucleation rates of NAT/NAD in ternary solutions have been determined from laboratory experiments (Koop et al, 1995(Koop et al, , 1997Salcedo et al, 2001;Knopf et al, 2002). Other laboratory studies with binary solutions show that the metastable NAD may form as the precursor of NAT, later performing a transition to NAT (Worsnop et al, 1993).…”

Section: Homogeneous Nat Nucleationmentioning

confidence: 99%

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

Voigt¹,

Schläger²,

Luo³

et al. 2005

Atmos. Chem. Phys.

171

189

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Abstract.A PSC was detected on 6 February 2003 in the Arctic stratosphere by in-situ measurements onboard the high-altitude research aircraft Geophysica. Low number densities (∼10 −4 cm −3 ) of small nitric acid (HNO 3 ) containing particles (d<6 µm) were observed at altitudes between 18 and 20 km. Provided the temperatures remain below the NAT equilibrium temperature T NAT , these NAT particles have the potential to grow further and to remove HNO 3 from the stratosphere, thereby enhancing polar ozone loss. Interestingly, the NAT particles formed in less than a day at temperatures just slightly below T NAT (T >T NAT −3.1 K). This unique measurement of PSC formation at extremely low NAT saturation ratios (S NAT 10) constrains current NAT nucleation theories. We suggest, that the NAT particles have formed heterogeneously, but for certain not on ice. Conversely, meteoritic particles may be favorable candidates for triggering NAT nucleation at the observed low number densities.

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Homogeneous Freezing of Concentrated Aqueous Nitric Acid Solutions at Polar Stratospheric Temperatures

Cited by 77 publications

References 33 publications

Formation of solid particles in synoptic-scale Arctic PSCs in early winter 2002/2003

Formation of solid particles in synoptic-scale Arctic PSCs in early winter 2002/2003

Does the Homogeneous Ice Nucleation Initiate in the Bulk Volume or at the Surface of Super-Cooled Water Droplets? A Review

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

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