Clouds freezing

Biermann, U.M. Prosper, T. MoBinger, J. Crutzen, P.J. Peter, T., 1996 The Unsuitability of Meteoritic and Other Nuclei for Polar Stratospheric Cloud Freezing , in Geophysical Research Letters, 23 1693-1696. 

Various fuel properties (Cloud, Freeze, etc.) for petroleum fractions Lognormal.xls... 

Freezing point NF M 07-048 ISO 3013 ASTM D 2386 Temperature of disappearance of cloud on reheating... 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

In order for rain to form, there must be particles in the air (i.c., dust or salt) around which the raindrop can form and which are at temperatures above freezing. When the particles are cooled to temperatures below the freezing point water condenses around them in layers. The particles grow heavy enough that they eventually fall through the clouds in the form of raindrops or— if the air temperature is below the freezing point all the way to the ground — as snow, sleet, or hail. 

Thermostable pectinesterases (TSPE), operationally defined as activity that survives 5 min at 70°C, contribute most to cloud loss in juices at low temperatures and juice pH (26). The percentage of total activity that is thermostable is highly variable and differs in kinetic properties, (22, 26), ease of solubilization (28, 29), stability to low pH (25) and stability to freeze-thaw cycles (23). Some of the variability in reported total PE and TSPE may be related to limitations of current methods to quantify activity. Any processing treatment or assay condition that increases cell wall breakdown or release PE from a pectin complex would enhance detection of total and TS-PE activity. Commercially, PE is inactivated by pasteurization in a plate heat exchanger or during concentration in the TASTE evaporator. 

However, one finds that, in cooling a liquid below its freezing point, the liquid may not always turn into solid phase at the freezing point. In fact, in some cases, such as water, even at around -40°C, liquid water does not turn into a solid phase. It stays in what is called a supercooled state. A major phenomena is the freezing of supercooled clouds. However, if certain so-called nucleating agents are used, then the clouds would turn into liquid droplets (and form rain). The nucleation process is a surface phenomena and is observed in transitions from... 

Nitrous acid/nitrite can also be oxidized in the aqueous solutions found in the atmosphere in the form of fogs, clouds, and particles. Nitrite is well known to be slowly oxidized in the dark to nitrate by dissolved oxygen in the liquid phase. However, it has been reported that the rate of this oxidation increases remarkably during freezing of the solution containing the nitrite (Takenaka et al., 1992, 1996). Figure 7.11, for example, shows the rate of nitrate formation in a nitrite solution at 25°C and in one with the cooling bath at — 21°C (Takenaka et al., 1992). This unusual phenomenon has also been observed with respect to the... 

Mitchell, North Carolina, Air Waste, 43, 1074-1083 (1993). Arakaki, T., C. Anastasio, P. G. Shu, and B. C. Faust, Aqueous-Phase Photoproduction of Hydrogen Peroxide in Authentic Cloud Waters Wavelength Dependence, and the Effects of Filtration and Freeze-Thaw Cycles, Atmos. Environ., 29, 1697-1703 (1995). Arakaki, T., and B. C. Faust, Sources, Sinks, and Mechanisms of Hydroxyl Radical ( OH) Photoproduction and Consumption in Authentic Acidic Continental Cloud Waters from Whiteface Mountain, New York The Role of the Fe(r) (r = II, III) Photochemical Cycle, . /. Geophys. Res., 103, 3487-3504 (1998). Atkinson, R., D. L. Baulch, R. A. Cox, R. F. Hampson, Jr., J. A. Kerr, M. J. Rossi, and J. Troe, Evaluated Kinetic and Photochemical... 

M. Loewenstein, G. V. Ferry, K. R. Chan, and B. L. Gary, Particle Size Distributions in Arctic Polar Stratospheric Clouds, Growth, and Freezing of Sulfuric Acid Droplets, and Implications for Cloud Formation, J. Geophys. Res., 97, 8015-8034 (1992). 

Song, N Freezing Temperatures of H 2S0,/HN03/H20 Mixtures —Implications for Polar Stratospheric Clouds, Geophys. Res. Lett., 21, 2709-2712 (1994). 

Consider a sample of rainwater from a cold cloud that is initially at temperature T= — 10°C and pressure P= 1 atm as it comes to earth. Will it freeze We can pose the question in terms of the initial state (water) and final state (ice) of the system ... 

Cloud Point (1%, C) 53 Surface tension (0.25% dynes/cm) 28.17 Viscosity, Brookfield (25C, LV 1, 100rpm, cps) 5.8 Freeze thaw stable freezing point (C) Did not freeze Procedure ... 

Petro BAF, in combination with sodium lauryl sulfate, reduces the low temperature cloud point, giving excellent freeze/thaw properties. The Petro BAF combination dries less tacky than sodium lauryl sulfate alone. 

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