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- Author or Editor: Farn Parungo x
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Abstract
Experiments of ice nucleation by silver iodide were conducted in a cold chamber at various temperatures. The seeded ice crystals were replicated and an examination of the position of AgI nuclei in individual ice crystals was made using an electron microscope. The mechanism of ice nucleation is discussed.
Abstract
Experiments of ice nucleation by silver iodide were conducted in a cold chamber at various temperatures. The seeded ice crystals were replicated and an examination of the position of AgI nuclei in individual ice crystals was made using an electron microscope. The mechanism of ice nucleation is discussed.
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To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager I and II launches. The aerosol's morphology, concentration and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an x-ray energy spectrometer. Ice nucleus concentration was measured with a subfreezing thermal diffusion chamber. The particles' physical and chemical properties were related to their ice nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei. Their consequences for potential inadvertant weather modification demand additional study.
Abstract
To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager I and II launches. The aerosol's morphology, concentration and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an x-ray energy spectrometer. Ice nucleus concentration was measured with a subfreezing thermal diffusion chamber. The particles' physical and chemical properties were related to their ice nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei. Their consequences for potential inadvertant weather modification demand additional study.
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Abstract
Samples of rain, snow, cloud water, aerosols and soil were collected in Colorado to study the mechanisms of acid rain formation. Chemical compositions of various types of samples were analyzed to investigate the stepwise incorporation of impurities into precipitation. Local soil was generally alkaline; atmospheric aerosols, which are mixtures of stirred-up soil particles and anthropogenic pollution, were slightly acidic; cloud condensation nuclei, which initiate clouds at condensation level, had an average pH of ∼6. However, local clouds were very acidic (pH ∼4), indicating that further acidification takes place in clouds by adsorption of acidic gases, e.g., CO2, SO2, and NO x . We found that summer showers formed by coalescence of cloud droplets are likely to be as acidic as cloud water. The chemistry of snow may differ from that of clouds, depending on the mechanisms of snow formation. If snow crystals are initiated by deposition nucleation and grown by diffusion of water vapor from surrounding evaporating cloud droplets as in the Bergeron-Findeisen process, the snow crystals are purified and should not be acidic. If the snow crystals are initiated by freezing of cloud droplets and grow by vapor diffusion, then the constituents of cloud water are diluted and the snow is less acidic than cloud water. If snow grains (graupel) are formed by accretion of frozen cloud drops or by riming, the snow can be as acidic as cloud water. Raindrops formed by melting snow inherit the chemistry of the parent snow, but differentiate in scavenging coefficiencies of gases and aerosols below the clouds. Both atmospheric chemical reactions and cloud microphysical processes are responsible for chemical variations in precipitation.
Abstract
Samples of rain, snow, cloud water, aerosols and soil were collected in Colorado to study the mechanisms of acid rain formation. Chemical compositions of various types of samples were analyzed to investigate the stepwise incorporation of impurities into precipitation. Local soil was generally alkaline; atmospheric aerosols, which are mixtures of stirred-up soil particles and anthropogenic pollution, were slightly acidic; cloud condensation nuclei, which initiate clouds at condensation level, had an average pH of ∼6. However, local clouds were very acidic (pH ∼4), indicating that further acidification takes place in clouds by adsorption of acidic gases, e.g., CO2, SO2, and NO x . We found that summer showers formed by coalescence of cloud droplets are likely to be as acidic as cloud water. The chemistry of snow may differ from that of clouds, depending on the mechanisms of snow formation. If snow crystals are initiated by deposition nucleation and grown by diffusion of water vapor from surrounding evaporating cloud droplets as in the Bergeron-Findeisen process, the snow crystals are purified and should not be acidic. If the snow crystals are initiated by freezing of cloud droplets and grow by vapor diffusion, then the constituents of cloud water are diluted and the snow is less acidic than cloud water. If snow grains (graupel) are formed by accretion of frozen cloud drops or by riming, the snow can be as acidic as cloud water. Raindrops formed by melting snow inherit the chemistry of the parent snow, but differentiate in scavenging coefficiencies of gases and aerosols below the clouds. Both atmospheric chemical reactions and cloud microphysical processes are responsible for chemical variations in precipitation.
Abstract
Results from measurements made to study the behavior of lead aerosols in Denver urban air as latent ice nuclei are discussed.
In the study, use was made of three independent measuring systems. These were: 1) an NCAR continuous ice nucleus counter with a capability to convert suspended lead compounds to lead iodide particles prior to passage through the cloud chamber and counting unit, 2) an atomic absorption spectrophotometer for analysis of lead content in collected air and rain water samples, and 3) the use of Tufts’ spot test for obtaining lead particle concentration and size distribution from collected Millipore filters. Both ground and airborne measurements were made.
Pertinent findings included: 1) good Qualitative agreement among the three types of measurements; 2) lead content of rain water an order of magnitude greater than silver concentration in seeded snow samples which were collected in a weather modification seeding target area using silver iodide as the seeding agent; and 3) 10-300 lead particles (latent ice nuclei) liter−1 existing up to 9000 ft above the surface when unstable temperature stratification existed and which were converted into active ice nuclei (lead iodide particles) when passed through an iodine vapor chamber.
Abstract
Results from measurements made to study the behavior of lead aerosols in Denver urban air as latent ice nuclei are discussed.
In the study, use was made of three independent measuring systems. These were: 1) an NCAR continuous ice nucleus counter with a capability to convert suspended lead compounds to lead iodide particles prior to passage through the cloud chamber and counting unit, 2) an atomic absorption spectrophotometer for analysis of lead content in collected air and rain water samples, and 3) the use of Tufts’ spot test for obtaining lead particle concentration and size distribution from collected Millipore filters. Both ground and airborne measurements were made.
Pertinent findings included: 1) good Qualitative agreement among the three types of measurements; 2) lead content of rain water an order of magnitude greater than silver concentration in seeded snow samples which were collected in a weather modification seeding target area using silver iodide as the seeding agent; and 3) 10-300 lead particles (latent ice nuclei) liter−1 existing up to 9000 ft above the surface when unstable temperature stratification existed and which were converted into active ice nuclei (lead iodide particles) when passed through an iodine vapor chamber.
Abstract
A procedure is presented for identifying those silver iodide particles in ice crystals that have behaved as snow crystal nuclei. The new technique is based on the principle that any submicron particle can act as a nucleus in its own superstaurated solution, and can grow to any desired crystal size (the final size depending on time of exposure to the supersaturated solution). For the procedure presented here, an aqueous solution of 30% potassium iodide supersaturated with silver iodide is used.
Application of the technique in a weather modification field research project is described. A case-study example is presented, and results of the season's experiments are discussed with emphasis on contributions of the nuclei identification data. It is concluded that the technique has considerable practical utility in qualitative determination of effects from cloud seeding.
Abstract
A procedure is presented for identifying those silver iodide particles in ice crystals that have behaved as snow crystal nuclei. The new technique is based on the principle that any submicron particle can act as a nucleus in its own superstaurated solution, and can grow to any desired crystal size (the final size depending on time of exposure to the supersaturated solution). For the procedure presented here, an aqueous solution of 30% potassium iodide supersaturated with silver iodide is used.
Application of the technique in a weather modification field research project is described. A case-study example is presented, and results of the season's experiments are discussed with emphasis on contributions of the nuclei identification data. It is concluded that the technique has considerable practical utility in qualitative determination of effects from cloud seeding.
