Does molecular HNO<sub>3</sub> adsorb onto sulfuric acid droplet surfaces?

Donaldson, D. J.; Anderson, Darren

doi:10.1029/1999gl010894

Cited by 23 publications

(37 citation statements)

References 23 publications

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“…Recent studies indicate that the surface of an aqueous particle is often enriched in low surface tension components such as molecular nitric acid (38,39) and organic materials (40)(41)(42). This surface adsorption effect in complex particle systems, which exist in the atmosphere, can have a 2-fold effect.…”

Section: Discussionmentioning

confidence: 99%

“…First, it is clear from Eqs. 2 and 3 that such surface enrichments (38)(39)(40)(41)(42) will make it more difficult for an ice nucleus to form at the surface layer of an aqueous droplet as compared with that of a pure water droplet. Second, the same surface adsorption effect can enrich the composition of the surface layer to a level where multicomponent solid phases can nucleate and grow.…”

Section: Discussionmentioning

confidence: 99%

“…Second, the same surface adsorption effect can enrich the composition of the surface layer to a level where multicomponent solid phases can nucleate and grow. For example, we have suggested (35) that the observed enrichment of molecular nitric acid (38,39) at the surface layer of an aqueous nitric acid solution droplet may lead to crystallization of hydrates of nitric acid at the droplet surface. Similarly, organic species in aerosols, which are often enriched at the surface layer (40)(41)(42), may nucleate to form condensable (or perhaps crystalline) species at or very near the surface layer of the particle.…”

Section: Discussionmentioning

confidence: 99%

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Surface crystallization of supercooled water in clouds

Tabazadeh

Djikaev

Reiss

2002

Proc. Natl. Acad. Sci. U.S.A.

227

249

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The process by which liquid cloud droplets homogeneously crystallize into ice is still not well understood. The ice nucleation process based on the standard and classical theory of homogeneous freezing initiates within the interior volume of a cloud droplet. Current experimental data on homogeneous freezing rates of ice in droplets of supercooled water, both in air and emulsion oil samples, show considerable scatter. For example, at ؊33°C, the reported volume-based freezing rates of ice in supercooled water vary by as many as 5 orders of magnitude, which is well outside the range of measurement uncertainties. Here, we show that the process of ice nucleus formation at the air (or oil)-liquid water interface may help to explain why experimental results on ice nucleation rates yield different results in different ambient phases. Our results also suggest that surface crystallization of ice in cloud droplets can explain why low amounts of supercooled water have been observed in the atmosphere near ؊40°C. For almost 200 years, persistent (liquid) fogs have been observed at temperatures well below the frost point, and there has been a continued vigorous interest in understanding why, and how far, water droplets can supercool in the atmosphere. The presence of heterogeneous ice nuclei in supercooled water droplets has been shown to be necessary for glaciating clouds at temperatures above about Ϫ30°C (1). However, ice particle number densities in clouds below Ϫ30°C are often observed to exceed the ice nuclei number densities (2-7). This finding suggests that, in clouds, some supercooled water droplets freeze homogeneously.The conversion of supercooled water droplets and͞or droplets of aqueous salt solutions into ice below Ϫ30°C can occur anywhere in the atmosphere from the surface layer (resulting in ice fogs) (8) to the upper troposphere (in cirrus clouds) (4-6). In addition, ice freezing in the polar stratosphere has been shown to occur via a homogeneous nucleation process (9, 10). Therefore, it is important to elucidate the actual physical process by means of which clouds glaciate in the atmosphere, particularly at cold temperatures and in situations where ice nuclei become less abundant and less effective in promoting the freezing of cloud droplets into ice (1).Radiative properties of ice clouds and their subsequent effect on climate depend strongly on the size of the cloud particles (11), a property closely linked to the rate at which ice particles in the cloud nucleate and grow. In addition, the rates of chemical reactions, which occur in cloud droplets or on cloud surfaces, depend on the phase of the cloud particle (12). Thus it is important to be able to predict under what set of environmental conditions supercooled cloud droplets freeze into ice. Other significant natural processes, which are affected by the physical state of clouds, include lightning (13) and precipitation. The occurrence of lightning can increase the concentration of reactive nitrogen oxides in air, thereby affecting the rate of gas-phase chem...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Surface crystallization of supercooled water in clouds

Tabazadeh

Djikaev

Reiss

2002

Proc. Natl. Acad. Sci. U.S.A.

227

249

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“…When considering liquid particle microphysics, we need to take into account the surface enrichment of HNO 3 in both binary HNO 3 =H 2 O and ternary HNO 3 /H 2 SO 4 /H 2 O solutions (Yang and FinlaysonPitts, 2001;Donaldson and Anderson, 1999), which could influence surface-based nucleation rates. In addition, the presence of H 2 SO 4 in STS droplets can strongly inhibit the nucleation of HNO 3 hydrates (Koop et al, 1997b).…”

Section: Article In Pressmentioning

confidence: 99%

Polar stratospheric cloud microphysics and chemistry

Lowe

MacKenzie

2008

Journal of Atmospheric and Solar-Terrestrial Physics

140

130

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“…Specifically, it has been shown that molecular nitric acid is enriched at the surface layer of aqueous solutions (Donaldson and Anderson, 1999;Yang and Finlayson-Pitts, 2001). Furthermore, our recent study (Djikaev et al, 2003) also shows that the level of surface enrichment of a given species in a multicomponent solution is a function of particle size.…”

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confidence: 99%

Commentary on "Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification" by Knopf et al.

Tabazadeh

2003

Atmos. Chem. Phys.

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Abstract. In a recent published paper Knopf et a1. (2002) have suggested that the homogeneous freezing behavior of stratospheric aerosols, under polar winter conditions, can be simulated experimentally in large bulk phase-sized droplet samples (0.12-0.27 cm in diameter). Their hypothesis is based on the fact that a nucleus, which freezes the supercooled phase, forms within the bulk volume of a given sample, and therefore, if large bulk volumes don't freeze in the laboratory, then small volumes in particles most certainly remain unfrozen in the stratosphere. The important question to ask here is whether their initial hypothesis, which they have used to analyze their data, is even correct to begin with. For example, does a nucleus, which turns over the phase, forms within the bulk volume or on the surface of the supercooled phase? Some recent studies provide both experimental (Tabazadeh et al., 2002a, b) and theoretical (Djikaev et al., 2002, 2003) support for the formation of the nucleus at the surface of a supercooled droplet. If the homogeneous nucleation process initiates at the droplet surface, then the approach taken by Knopf. et al. to study this crystallization process may not be directly applicable to the stratospheric situation.

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Does molecular HNO₃ adsorb onto sulfuric acid droplet surfaces?

Cited by 23 publications

References 23 publications

Surface crystallization of supercooled water in clouds

Surface crystallization of supercooled water in clouds

Polar stratospheric cloud microphysics and chemistry

Commentary on "Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification" by Knopf et al.

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Does molecular HNO3 adsorb onto sulfuric acid droplet surfaces?

Cited by 23 publications

References 23 publications

Surface crystallization of supercooled water in clouds

Surface crystallization of supercooled water in clouds

Polar stratospheric cloud microphysics and chemistry

Commentary on &quot;Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification&quot; by Knopf et al.

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Does molecular HNO₃ adsorb onto sulfuric acid droplet surfaces?

Commentary on "Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification" by Knopf et al.