scholarly journals High homogeneous freezing onsets of sulfuric acid aerosol at cirrus temperatures

2021 ◽  
Vol 21 (18) ◽  
pp. 14403-14425
Author(s):  
Julia Schneider ◽  
Kristina Höhler ◽  
Robert Wagner ◽  
Harald Saathoff ◽  
Martin Schnaiter ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Water Activity ◽  
Nucleation Rate ◽  
Aerosol Particles ◽  
Rate Coefficients ◽  
Cirrus Cloud ◽  
Aqueous Sulfuric Acid ◽  
Wide Range ◽  
Formation Conditions ◽  
Homogeneous Freezing

Abstract. Homogeneous freezing of aqueous solution aerosol particles is an important process for cloud ice formation in the upper troposphere. There the air temperature is low, the ice supersaturation can be high and the concentration of ice-nucleating particles is too low to initiate and dominate cirrus cloud formation by heterogeneous ice nucleation processes. The most common description to quantify homogeneous freezing processes is based on the water activity criterion (WAC) as proposed by Koop et al. (2000). The WAC describes the homogeneous nucleation rate coefficients only as a function of the water activity, which makes this approach well applicable in numerical models. In this study, we investigate the homogeneous freezing behavior of aqueous sulfuric acid aerosol particles by means of a comprehensive collection of laboratory-based homogeneous freezing experiments conducted at the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud simulation chamber, which were conducted as part of 17 measurement campaigns since 2007. The most recent experiments were conducted during October 2020 with special emphasis on temperatures below 200 K. Aqueous sulfuric acid aerosol particles of high purity were generated by particle nucleation in a gas flow composed of clean synthetic air and sulfuric acid vapor, which was added to the AIDA chamber. The resulting chamber aerosol had number concentrations from 30 cm−3 up to several thousand per cubic centimeter with particle diameters ranging from about 30 nm to 1.1 µm. Homogeneous freezing of the aerosol particles was measured at simulated cirrus formation conditions in a wide range of temperatures between 185 and 230 K with a steady increase of relative humidity during each experiment. At temperatures between about 205 K and about 230 K, the AIDA results agree well with the WAC-based predictions of homogeneous freezing onsets. At lower temperatures, however, the AIDA results show an increasing deviation from the WAC-based predictions towards higher freezing onsets. For temperatures between 185 and 205 K, the WAC-based ice saturation ratios for homogeneous freezing onsets increase from about 1.6 to 1.7, whereas the AIDA measurements show an increase from about 1.7 to 2.0 in the same temperature range. Based on the experimental results of our direct measurements, we suggest a new fit line to formulate the onset conditions of homogeneous freezing of sulfuric acid aerosol particles as an isoline for nucleation rate coefficients between 5×108 and 1013 cm−3 s−1. The potential significant impacts of the higher homogeneous freezing thresholds, as directly observed in the AIDA experiments under simulated cirrus formation conditions, on the model prediction of cirrus cloud occurrence and related cloud radiative effects are discussed.

scholarly journals High Homogeneous Freezing Onsets of Sulfuric Acid Aerosol at Cirrus Temperatures

2021 ◽  
Author(s):  
Julia Schneider ◽  
Kristina Höhler ◽  
Robert Wagner ◽  
Harald Saathoff ◽  
Martin Schnaiter ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Water Activity ◽  
Numerical Models ◽  
Aerosol Particles ◽  
Cirrus Cloud ◽  
Particle Nucleation ◽  
Acid Vapor ◽  
Aqueous Sulfuric Acid ◽  
Wide Range ◽  
Homogeneous Freezing

Abstract. Homogeneous freezing of aqueous solution aerosol particles is an important process for cloud ice formation in theupper troposphere. There the air temperature is low, the ice supersaturation can be high, and the concentration of ice-nucleating particles is too low to initiate and dominate cirrus cloud formation by heterogeneous ice nucleation processes. The most common description to quantify homogeneous freezing processes is based on the water activity criterion (WAC) as proposed by Koop et al. (2000). The WAC describes the homogeneous nucleation rate coefficients only as a function of the water activity, temperature and size of the aqueous aerosol particles, which makes this approach well applicable in numerical models. In this study, we investigate the homogeneous freezing behaviour of aqueous sulfuric acid aerosol particles by means of a comprehensive collection of laboratory homogeneous freezing experiments conducted at the AIDA (Aerosol Interaction and Dynamicsin the Atmosphere) cloud simulation chamber, which were conducted as part of 17 measurement campaigns since 2007. The most recent experiments were conducted during October 2020 with special emphasis on temperatures below 200 K. Aqueous sulfuric acid aerosol particles were generated at high purity by particle nucleation in a gas flow composed of clean synthetic air and sulfuric acid vapor, which was added to the AIDA chamber. The resulting chamber aerosol had number concentrations from 30 cm−3 up to several 1000 cm−3 with particle diameters ranging from about 30 nm to 1.1 μm. Homogeneous freezing of the aerosol particles was measured at simulated cirrus formation conditions in a wide range of temperatures between 185 K and 230 K with a steady increase of relative humidity during each experiment. At temperatures between about 205 K and about 230 K, the AIDA results agree well with the WAC-based predictions of homogeneous freezing onsets. At lower temperatures, however, the AIDA results show an increasing deviation from the WAC-based predictions towards higher freezing onsets. For temperatures between 185 K and 205 K, the WAC-based ice saturation ratios for homogeneous freezing onsets increase from about 1.6 to 1.7, whereas the AIDA measurements show an increase from about 1.7 to 2.0 in the same temperature range. Based on our experimental results, we suggest a new fit line as a parameterization for the onset conditions of homogeneous freezing of sulfuric acid aerosol particles. As a next step, we propose the new parameterization to be implemented in atmospheric models as an improved version of the WAC-based parameterization from Koop et al. (2000). The new homogeneous freezing thresholds may have significant impacts on the prediction of cirrus cloud occurrence and related cloud radiative effects.

scholarly journals Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

2006 ◽  
Vol 6 (11) ◽  
pp. 3231-3242 ◽  
Author(s):  
M. R. Beaver ◽  
M. J. Elrod ◽  
R. M. Garland ◽  
M. A. Tolbert
Keyword(s):  
Sulfuric Acid ◽  
Organic Compounds ◽  
Ice Nucleation ◽  
Organic Content ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Flow Tube ◽  
Melting Temperatures ◽  
Aqueous Sulfuric Acid ◽  
Sulfuric Acid Aerosols

Abstract. Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

scholarly journals Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

2005 ◽  
Vol 5 (3) ◽  
pp. 3391-3436 ◽  
Author(s):  
C. M. Archuleta ◽  
P. J. DeMott ◽  
S. M. Kreidenweis
Keyword(s):  
Sulfuric Acid ◽  
Relative Humidity ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Nucleation Behavior ◽  
Ice Nuclei ◽  
Homogeneous Freezing

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between −45 and −60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

scholarly journals Ice nucleation in sulfuric acid/organic aerosols: implications for cirrus cloud formation

2006 ◽  
Vol 6 (2) ◽  
pp. 2059-2090
Author(s):  
M. R. Beaver ◽  
M. J. Elrod ◽  
R. M. Garland ◽  
M. A. Tolbert
Keyword(s):  
Sulfuric Acid ◽  
Organic Compounds ◽  
Ice Nucleation ◽  
Organic Content ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Flow Tube ◽  
Melting Temperatures ◽  
Aqueous Sulfuric Acid ◽  
Sulfuric Acid Aerosols

Abstract. Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

scholarly journals Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation – monodisperse ice nuclei

2008 ◽  
Vol 8 (4) ◽  
pp. 15665-15698 ◽  
Author(s):  
D. Barahona ◽  
A. Nenes
Keyword(s):  
Number Concentration ◽  
Cloud Formation ◽  
Ice Formation ◽  
Average Error ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Ice Nuclei ◽  
Wide Range ◽  
Homogeneous Freezing ◽  
Nuclei Number

Abstract. We present a parameterization of cirrus cloud formation that computes the ice crystal number and size distribution under the presence of homogeneous and heterogeneous freezing. The parameterization is very simple to apply and is derived from the analytical solution of the cloud parcel equations, assuming that the ice nuclei population is monodisperse and chemically homogeneous. In addition to the ice distribution, an analytical expression is provided for the limiting ice nuclei number concentration that suppresses ice formation from homogeneous freezing. The parameterization is evaluated against a detailed numerical parcel model, and reproduces numerical simulations over a wide range of conditions with an average error of 6±33%.

scholarly journals Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

2005 ◽  
Vol 5 (10) ◽  
pp. 2617-2634 ◽  
Author(s):  
C. M. Archuleta ◽  
P. J. DeMott ◽  
S. M. Kreidenweis
Keyword(s):  
Sulfuric Acid ◽  
Relative Humidity ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Nucleation Behavior ◽  
Ice Nuclei ◽  
Homogeneous Freezing

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between -45 and -60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

scholarly journals Ice nucleation from aqueous NaCl droplets with and without marine diatoms

2011 ◽  
Vol 11 (3) ◽  
pp. 8291-8336 ◽  
Author(s):  
P. A. Alpert ◽  
J. Y. Aller ◽  
D. A. Knopf
Keyword(s):  
Surface Area ◽  
Water Activity ◽  
Nucleation Rate ◽  
Particle Production ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Rate Coefficients ◽  
Freezing Temperatures ◽  
Aqueous Volume ◽  
Heterogeneous Ice Nucleation

Abstract. Ice formation in the atmosphere by homogeneous and heterogeneous nucleation is one of the least understood processes in cloud microphysics and climate. Here we describe our investigation of the marine environment as a potential source of atmospheric IN by experimentally observing homogeneous ice nucleation from aqueous NaCl droplets and comparing against heterogeneous ice nucleation from aqueous NaCl droplets containing intact and fragmented diatoms. Homogeneous and heterogeneous ice nucleation are studied as a function of temperature and water activity, aw. Additional analyses are presented on the dependence of diatom surface area and aqueous volume on heterogeneous freezing temperatures, ice nucleation rates, ωhet, ice nucleation rate coefficients, Jhet, and differential and cumulative ice nuclei spectra, k(T) and K(T), respectively. Homogeneous freezing temperatures and corresponding nucleation rate coefficients are in agreement with the water activity based homogeneous ice nucleation theory within experimental and predictive uncertainties. Our results confirm, as predicted by classical nucleation theory, that a stochastic interpretation can be used to describe this nucleation process. Heterogeneous ice nucleation initiated by intact and fragmented diatoms can be adequately represented by a modified water activity based ice nucleation theory. A horizontal shift in water activity, Δaw, het = 0.2303, of the ice melting curve can describe median heterogeneous freezing temperatures. Individual freezing temperatures showed no dependence on available diatom surface area and aqueous volume. Determined at median diatom freezing temperatures for aw from 0.8 to 0.99, ωhet ~ 0.11+0.06−0.05 s−1, Jhet ~ 1.0+1.16−0.61 × 104 cm−2 s−1, and K ~ 6.2+3.5−4.1 × 104 cm−2. The experimentally derived ice nucleation rates and nuclei spectra allow us to estimate ice particle production which we subsequently use for a comparison with observed ice crystal concentrations typically found in cirrus and polar marine mixed-phase clouds. Differences in application of time-dependent and time-independent analyses to predict ice particle production are discussed.

scholarly journals Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation – monodisperse ice nuclei

2009 ◽  
Vol 9 (2) ◽  
pp. 369-381 ◽  
Author(s):  
D. Barahona ◽  
A. Nenes
Keyword(s):  
Number Concentration ◽  
Cloud Formation ◽  
Ice Formation ◽  
Average Error ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Ice Nuclei ◽  
Wide Range ◽  
Homogeneous Freezing ◽  
Nuclei Number

Abstract. We present a parameterization of cirrus cloud formation that computes the ice crystal number and size distribution under the presence of homogeneous and heterogeneous freezing. The parameterization is very simple to apply and is derived from the analytical solution of the cloud parcel equations, assuming that the ice nuclei population is monodisperse and chemically homogeneous. In addition to the ice distribution, an analytical expression is provided for the limiting ice nuclei number concentration that suppresses ice formation from homogeneous freezing. The parameterization is evaluated against a detailed numerical parcel model, and reproduces numerical simulations over a wide range of conditions with an average error of 6±33%. The parameterization also compares favorably against other formulations that require some form of numerical integration.

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