The Colorado/Missouri 1989 cirrus mini IFO

A series of experiments with aircraft were planned for Nov. and Dec. 1989 to study cirrus ice crystal nucleation mechanisms and to test new aircraft instrumentation. The measurements were conducted using the NCAR Sabreliner and King Air. Sampling was conducted near Boulder, Colorado, in lenticular (mountain wave) clouds, and over Missouri in cirrus generating cells. Field samples of aerosol and ice crystal replicas and melt water from these cirrus clouds were collected and studied. Aircraft instrumentation and sampling techniques are discussed

Structural Strain in Small Prenucleation Water Clusters

A method is developed for incorporating strain energy into a microphysical treatment of small prenucleation water clusters. The molecules are arranged in a clathrate-cage structure, and this structure is allowed to relax to minimize the strain energy resulting from hydrogen bond stretching and bending. The method is applied to various cluster sizes up to 130 molecules and the results are compared with the classical liquid drop model. The effect of anharmonic terms in the interaction is included

Adsorption of Rare Gas Atoms on Xenon

The problem of adsorption of rare gas atoms on solids is treated for the case of submonolayer films. An energy spectrum calculation method which is suitable for band structure or heat capacity calculations is discussed. It is particularly useful for adsorbate-substrate systems in the region intermediate between tight binding and plane wave behavior. The method employs a technique introduced by Kohn and Luttinger of using the eigenfunctions corresponding to a particular point in the Brillouin zone as a basis set. The cases of He and Ne adsorbed on Xe are discussed

Homogeneous Nucleation Rate for Water

Homogeneous nucleation rate data for water extending over an exceptionally large domain of rate (J), supersaturation ratio (S), and temperature (T) was recently published. Because it spans a large J-S-T surface, this data constitutes a good test of nucleation theory. Here classical nucleation theory is used to analyze this data. By adjusting only the sticking coefficient, we are able to obtain a good fit between theory and experiment. It was necessary to include an increase in the water molecular density associated with the finite water compressibility

Upper-Tropospheric Aerosol Sampled During Project Fire IFO II

Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropospause, and there was a tendency toward depletion of the ambient aerosol at both ends of the condensation nuclei (CN) size distribution

Invesigation of Solid Molecular Complexes of Picric Acid

Chemistr

Measured Spectra of the Hygroscopic Fraction of Atmospheric Aerosol Particles

The relation between dry diameter (X0) and critical supersaturation (Sc) for atmospheric submicron aerosol particles is investigated using a long term air sampling program at Rolla, Missouri. The particles are passed through an electrostatic aerosol size classifier, and then through an isothermal haze chamber. Results are reported in terms of an apparent volume fraction of soluble material, εv defined such that for particles composed only of ammonium sulfate and water insoluble compounds, εv is the actual volume fraction of soluble material. The probability distribution of εv is found to be approximately Gaussian in the εv range 0.2 to 1.3. The mean εv is 0.5, for electrostatic aerosol classifier settings of 0.2, 0.3, and 0.4 μm diameter

Intercomparison between Commercial Condensation Nucleus Counters and an Alternating Temperature Gradient Cloud Chamber

Three Commercial CNC Counters (TSI Models 3010, 3022A, and 3025A) Are Compared with an Alternating Temperature Gradient Cloud Chamber (ALGR). Electrically Size Classified Aerosols of Sodium Chloride and Silver Are Used. Diffusional Losses within the ALGR Are Much Larger Than for the TSI Instruments: Therefore the ALGR Concentrations Are Corrected for Internal Diffusional Losses, But the TSI Instruments Are Not. the Particle Size Range Tested is 4–90 Nm. for Sodium Chloride, the TSI Concentrations Agreed Fairly Well with the Corrected ALGR at Larger Sizes, and Were Below the Corrected ALGR at Smaller Sizes. the Electrical Aerosol Classifier (EAC) Setting at Which a Particular TSI Instrument Concentration is 50% of the Corrected ALGR Concentration is Denoted D 50%. for the 3010 and 3022A, the Values of D 50% Are 14.5 and 7.9 Nm, Respectively. for the 3025A the Extrapolated D 50% is 3.5 Nm. These D 50% Values Are Close to Those Reported for Comparisons between Concentrations Measured by the TSI Instruments and Concentrations Determined with an Aerosol Electrometer. However, the Count Ratio Rises to Unity Less Quickly as Size Increases for the Present Intercomparisons as Compared with Intercomparisons with Aerosol Electrometers. the ALGR Can Produce at Most a 30% Water Super-Saturation, Corresponding to a Kelvin Diameter of 8.4 Nm. Thus, Since Silver Particles Are Water Insoluble, the ALGR Detected Small Silver Particles Less Efficiently Than the TSI Model 3025A. the Data with Silver Aerosols Allowed Determination of the Relation between Size and Critical Supersaturation over the Size Range 16–30 Nm Diameter. the Silver Aerosol Exhibited Critical Supersaturations Higher, by a Factor of 1.2 to 1.8, Than Those Given by the Kelvin Equation. © 1995 American Association for Aerosol Research Published by Elsevier Science Inc