The Effect of Relative Humidity on the Nucleating Properties of Photolyzed Silver Iodide *

The effect of adsorbed water vapor on the photolysis of silver iodide has been studied. Inn has found that when silver iodide nuclei are exposed to ultraviolet light before injection into a cold chamber containing a cloud of supercooled water droplets, no ice formation is observed. Reynolds, Hume, Vonnegut and Schaefer have investigated the effect of bright sunlight on the action of silver iodide as a sublimation nucleus, and have found a decrease in the magnitude of nucleating effectiveness which is less than that observed by Inn. The studies in this laboratory have been concerned with the effect of relative humidity on the photolysis and subsequent nucleating properties of silver iodide particles. Known amounts of water vapor were introduced into a stream of nitrogen passing over a silver iodide generator. The silver iodide particles, covered with adsorbed water, were collected in a cell and exposed to ultraviolet light of known intensity for varying amounts of time. After irradiation, the silver iodide particles were injected into a cloud of supercooled water droplets and ice formation was watched for. The nucleating effectiveness of silver iodide exposed to ultraviolet light was found to be directly dependent on the relative humidity of the gas stream passing over the generator.

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Freezing of water droplets colliding with kaolinite particles

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-4295-2009 ◽

2009 ◽

Vol 9 (13) ◽

pp. 4295-4300 ◽

Cited By ~ 28

Author(s):

E. A. Svensson ◽

C. Delval ◽

P. von Hessberg ◽

M. S. Johnson ◽

J. B. C. Pettersson

Keyword(s):

Water Vapor ◽

Relative Humidity ◽

Water Droplet ◽

Supercooled Water ◽

Dust Particles ◽

Freezing Process ◽

Water Droplets ◽

Electrodynamic Balance ◽

Dry Conditions

Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under relatively dry conditions (when no water vapor was added) freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed when water vapor was added to the air in the chamber. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. Mechanisms for contact freezing are briefly discussed.

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Effects of Sunlight and Ammonia on the Action of Silver-Iodide Particles as Sublimation Nuclei *

Bulletin of the American Meteorological Society ◽

10.1175/1520-0477-33.1.26 ◽

1952 ◽

Vol 33 (1) ◽

pp. 26-31 ◽

Cited By ~ 10

Author(s):

S. E. Reynolds ◽

William Hume ◽

Max McWhirter

Keyword(s):

Ultraviolet Light ◽

Silver Iodide ◽

Ice Crystals ◽

Ammonia Vapor ◽

Large Numbers ◽

Bright Sunlight ◽

Rate Of Decay

Tests involving exposure of AgI smoke to bright sunlight show a decrease in concentration of effective nuclei (at −20°C) of approximately two orders of magnitude per hour. The concentration of effective nuclei is increased greatly (as much as two orders of magnitude) by the addition of a little ammonia vapor to the AgI smoke. Smoke samples which have been deactivated completely by exposure to ultraviolet light can be caused to form large numbers of ice crystals by the addition of ammonia vapor. If ammonia is added before exposure to light, the rate of decay is the same or greater, and the effectiveness cannot be restored by further addition of ammonia. The effect of ammonia is believed to be due to the adsorption of ammonia on the silver iodide surfaces or to the formation of an ammine of silver iodide.

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The hydrogen bonding structure of adsorbed water on silver iodide and Feldspar minerals

10.5194/egusphere-egu2020-13167 ◽

2020 ◽

Author(s):

Markus Ammann ◽

Huanyu Yang ◽

Luca Artiglia ◽

Anthony Boucly

Keyword(s):

Hydrogen Bonding ◽

Water Vapor ◽

Silver Iodide ◽

Adsorbed Water ◽

Photoelectron Spectra ◽

Water Molecules ◽

Xps Spectra ◽

X Ray ◽

Bonding Structure ◽

Electron Yield

<p>The hydrogen bonding structure of adsorbed water on a solid substrate may control deposition nucleation, which is a pathway of heterogeneous ice nucleation. Hydrogen bonding of water molecules is also controlling the interface between the solid and liquid water relevant for other heterogeneous freezing modes. The hydrogen bonding structure may be affected by short and long-range interactions between the substrate and the water molecules nearby. Electron yield near edge X-ray absorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge is used to experimentally explore the difference between the hydrogen bonding structure of interfacial H<sub>2</sub>O molecules under different conditions of temperature and water vapor pressure. Experiments reported in this work were performed at the in-situ electron spectroscopy endstation at the ISS beamline at the Swiss Light Source (PSI, SLS). We report electron yield oxygen K-edge NEXAFS spectra and X-ray photoelectron spectra from silver iodide (AgI) particles and milled feldspar samples exposed to water vapor at high relative humidity, but subsaturated with respect to ice. AgI serves as a well-studied reference case; and it contains no oxygen in its lattice, which simplifies the analysis of NEXAFS spectra at the O K-edge. The feldspar samples include a potassium containing microcline and a sodium-rich albite. The analysis of the NEXAFS spectra indicate rather tetrahedrally coordinated adsorbed water molecules on AgI particles. On the feldspars, the mobility of ions, as directly observed by the XPS spectra appears to have a strong impact on the hydrogen bonding structure, as apparent from substantial differences between samples previously immersed in pure water or as prepared. To sum up, we attempt to understand the behavior of the hydrogen bonding structure, which provides rich information about the arrangement of water molecules in the vicinity of a solid surface, that is linked to the ability of the solid to induce ice formation.</p>

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Effects of Water Vapor, Ammonia and Hydrogen Sulfide gainst the Decay of Silver Iodide Smoke under rradiation of Ultraviolet Light

Journal of the Meteorological Society of Japan Ser II ◽

10.2151/jmsj1923.34.1_34 ◽

1956 ◽

Vol 34 (1) ◽

pp. 34-40 ◽

Cited By ~ 4

Keyword(s):

Hydrogen Sulfide ◽

Water Vapor ◽

Ultraviolet Light ◽

Silver Iodide

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A systematic experimental study on the evaporation rate of supercooled water droplets at subzero temperatures and varying relative humidity

Experiments in Fluids ◽

10.1007/s00348-017-2339-5 ◽

2017 ◽

Vol 58 (5) ◽

Cited By ~ 5

Author(s):

S. Ruberto ◽

J. Reutzsch ◽

N. Roth ◽

B. Weigand

Keyword(s):

Experimental Study ◽

Relative Humidity ◽

Evaporation Rate ◽

Supercooled Water ◽

Water Droplets ◽

Subzero Temperatures

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Experimental investigation of the evaporation rate of supercooled water droplets at constant temperature and varying relative humidity

International Communications in Heat and Mass Transfer ◽

10.1016/j.icheatmasstransfer.2016.08.005 ◽

2016 ◽

Vol 77 ◽

pp. 190-194 ◽

Cited By ~ 4

Author(s):

S. Ruberto ◽

J. Reutzsch ◽

B. Weigand

Keyword(s):

Experimental Investigation ◽

Relative Humidity ◽

Constant Temperature ◽

Evaporation Rate ◽

Supercooled Water ◽

Water Droplets

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Freezing of water droplets colliding with kaolinite particles

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-2417-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 2417-2433

Author(s):

E. A. Svensson ◽

C. Delval ◽

P. von Hessberg ◽

M. S. Johnson ◽

J. B. C. Pettersson

Keyword(s):

Relative Humidity ◽

Aerosol Particles ◽

Supercooled Water ◽

Dust Particles ◽

Freezing Process ◽

Atmospheric Conditions ◽

Water Droplets ◽

Electrodynamic Balance ◽

Dry Conditions ◽

Modelling Studies

Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under dry conditions freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed at high relative humidity. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. The data recorded at high humidity should be most relevant to atmospheric conditions, and the results indicate that parameterizations currently used in modelling studies to describe freezing rates are appropriate for kaolinite aerosol particles. Mechanisms for contact freezing are briefly discussed.

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HGPT2: An ERA5-Based Global Model to Estimate Relative Humidity

Remote Sensing ◽

10.3390/rs13112179 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2179

Author(s):

Pedro Mateus ◽

Virgílio B. Mendes ◽

Sandra M. Plecha

Keyword(s):

Water Vapor ◽

Relative Humidity ◽

Real Time ◽

Prediction Models ◽

Weather Prediction ◽

Precipitable Water ◽

Precipitable Water Vapor ◽

Global Navigation Satellite Systems ◽

International Gnss Service ◽

Weighted Mean Temperature

The neutral atmospheric delay is one of the major error sources in Space Geodesy techniques such as Global Navigation Satellite Systems (GNSS), and its modeling for high accuracy applications can be challenging. Improving the modeling of the atmospheric delays (hydrostatic and non-hydrostatic) also leads to a more accurate and precise precipitable water vapor estimation (PWV), mostly in real-time applications, where models play an important role, since numerical weather prediction models cannot be used for real-time processing or forecasting. This study developed an improved version of the Hourly Global Pressure and Temperature (HGPT) model, the HGPT2. It is based on 20 years of ERA5 reanalysis data at full spatial (0.25° × 0.25°) and temporal resolution (1-h). Apart from surface air temperature, surface pressure, zenith hydrostatic delay, and weighted mean temperature, the updated model also provides information regarding the relative humidity, zenith non-hydrostatic delay, and precipitable water vapor. The HGPT2 is based on the time-segmentation concept and uses the annual, semi-annual, and quarterly periodicities to calculate the relative humidity anywhere on the Earth’s surface. Data from 282 moisture sensors located close to GNSS stations during 1 year (2020) were used to assess the model coefficients. The HGPT2 meteorological parameters were used to process 35 GNSS sites belonging to the International GNSS Service (IGS) using the GAMIT/GLOBK software package. Results show a decreased root-mean-square error (RMSE) and bias values relative to the most used zenith delay models, with a significant impact on the height component. The HGPT2 was developed to be applied in the most diverse areas that can significantly benefit from an ERA5 full-resolution model.

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