Clouds chemistry and

Since 1990, Ramanathan has been Victor C.AIderson Professor of Applied Ocean Sciences and Professor of Climate and Atmospheric Sciences at the Scripps Institution of Oceanography in San Diego. In 1991 he was appointed director of the Center for Clouds, Chemistry, and Climate at Scripps, and in 1996, he became director of the Center for Atmospheric Sciences at the institution. 

Crutzen, P. J., and V. Ramanathan, Clouds, Chemistry and Climate, NATO ASI Series, Series I, Vol. 35, Springer-Verlag, Berlin, 1996. 

It is clear from the information presented above that liquid phase oxidation of reduced sulfur compounds play an important role in natural processes in water and in wastewater treatments. However, further work is needed to clarify the role of these compounds in cloud chemistry and precipitation acidity. Areas of further investigations should include ... 

Schwartz S. E. and Slingo A. (1996) Enhanced shortwave cloud radiative forcing due to anthropogenic aerosols. In Clouds, Chemistry, and Climate—Proceedings of NATO Advanced Research Workshop (eds. P. Crutzen and V. Ramanathan). Springer, Heidelberg, pp. 191-236. 

This article has not addressed several subjects in the field of cloud physics. For cloud chemistry and cloud electrification, see Atmospheric Chemistry and Atmospheric Electricity. The topic of cloud radiation and optics is almost as broad as that of cloud physics itself The reader is referred to the Bibliography for information on this topic. 

Lindinger 1984). Rather, we are concerned with the question as to what extent, and under what astrophysical circumstances, may drift tube data be properly applied to elucidate interstellar chemistry, specifically diffuse and dense cloud chemistry and to the chemistry of the shocked regions of interstellar gas. Towards this end, we present some sample data relating to atomic ion reactions which are believed to be applicable to interstellar chemistry and also some other drift tube data relating to molecular ion reactions which illustrate the influence of internal excitation of the molecular ions on their reactivity. 

Cmtzen, Paul J. Ramanathan, Veerabhadran (Eds.), 1996 Clouds, Chemistry and Climate,... 

In this section, the wide diversity of teclmiques used to explore ion chemistry and ion structure will be outlined and a sampling of the applications of ion chemistry will be given in studies of lamps, lasers, plasma processing, ionospheres and interstellar clouds. 

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. 

Heterogeneous chemistry occurring on polar stratospheric cloud particles of ice and nitric acid trihydrate has been estabUshed as a dorninant factor in the aggravated seasonal depletion of o2one observed to occur over Antarctica. Preliminary attempts have been made to parameterize this chemistry and incorporate it in models to study ozone depletion over the poles (91) as well as the potential role of sulfate particles throughout the stratosphere (92). 

When NMHC are significant in concentration, differences in their oxidation mechanisms such as how the NMHC chemistry was parameterized, details of R02-/R02 recombination (95), and heterogenous chemistry also contribute to differences in computed [HO ]. Recently, the sensitivity of [HO ] to non-methane hydrocarbon oxidation was studied in the context of the remote marine boundary-layer (156). It was concluded that differences in radical-radical recombination mechanisms (R02 /R02 ) can cause significant differences in computed [HO ] in regions of low NO and NMHC levels. The effect of cloud chemistry in the troposphere has also recently been studied (151,180). The rapid aqueous-phase breakdown of formaldehyde in the presence of clouds reduces the source of HOj due to RIO. In addition, the dissolution in clouds of a NO reservoir (N2O5) at night reduces the formation of HO and CH2O due to R6-RIO and R13. Predictions for HO and HO2 concentrations with cloud chemistry considered compared to predictions without cloud chemistry are 10-40% lower for HO and 10-45% lower for HO2. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

ION-MOLECULE CHEMISTRY IN INTERSTELLAR CLOUDS SUCCESSES AND PROBLEMS Eric Herbst 1... 

Gas-phase ion chemistry is a broad field which has many applications and which encompasses various branches of chemistry and physics. An application that draws together many of these branches is the synthesis of molecules in interstellar clouds (Herbst). This was part of the motivation for studies on the neutralization of ions by electrons (Johnsen and Mitchell) and on isomerization in ion-neutral associations (Adams and Fisher). The results of investigations of particular aspects of ion dynamics are presented in these association studies, in studies of the intermediates of binary ion-molecule Sn2 reactions (Hase, Wang, and Peslherbe), and in those of excited states of ions and their associated neutrals (Richard, Lu, Walker, and Weisshaar). Solvation in ion-molecule reactions is discussed (Castleman) and extended to include multiply charged ions by the application of electrospray techniques (Klassen, Ho, Blades, and Kebarle). These studies also provide a wealth of information on reaction thermodynamics which is critical in determining reaction spontaneity and availability of reaction channels. More focused studies relating to the ionization process and its nature are presented in the final chapter (Harland and Vallance). 

The estimate of the distance must now consider the estimate of the interstellar extinction Av, best estimated by the reddening Av can take several values and in calculations of molecular cloud chemistry typical values are of order 1 but may be as much as 5. The distance calculation in Equation 5.1 can be significantly perturbed so that an A v of 2.4 can reduce the apparent distance by a factor of 3. 

The improvement in the rate of chemical reactions is reversed when temperature is cooler and at temperatures as low as 30 K (a warm comer of TMC-1) the exponential term is of order 10-279 and nearly all reactions between neutral species are frozen out at 50 K. Two important classes of reactions survive radical-radical chemistry and ion-molecule chemistry. The importance of these different reaction types will become apparent later with the construction of the models of molecular clouds. For the moment, however, laboratory measurements of reactions in radicals such as C2H have shown that even with temperatures as low as 15 K the rate constant for reactions of the type ... 

The lifetime of the molecular cloud is considered to be a time line running from cloud formation, star evolution and finally dispersion in a period that is several tci. The chemistry of the TMC and, to a good approximation, all molecular clouds must then be propagated over a timescale of at most 20 million years. The model must then investigate the chemistry as a function of the age of the cloud, opening the possibility of early-time chemistry and hence species present in the cloud being diagnostic of the age of the cloud. The model should then expect to produce an estimated lifetime and the appropriate column densities for the known species in the cloud. For TMC-1 the species list and concentrations are shown in Table 5.4. 

Throughout this book you have been studying traditional chemistry and chemical reactions. This has involved the transfer or sharing of electrons from the electron clouds, especially the valence electrons. Little has been said up to this point regarding the nucleus. Now we are going to shift our attention to nuclear reactions and, for the most part, ignore the electron clouds. 

Advances in Gas Phase Ion Chemistry is different from other ion chemistry series in that it focuses on reviews of the author s own work rather than give a generai review of the research area. This allows for presentation of some current work in a timely fashion which marks the unique nature of this series. Emphasis is placed on gas phase ion chemistry in its broadest sense to include ion neutral, ion electron, and ion-ion reactions. These reaction processes span the various disciplines of chemistry and include some of those in physics. Within this scope, both experimental and theoretical contributions are included which deal with a wide variety of areas ranging from fundamental interactions to applications in real media such as Interstellar gas clouds and pleismas used in the etching of semiconductors. The authors are scientists who are leaders in their fields and the series will therefore provide an up-to-date analysis of topics of current importance. This series is suitable for researchers and graduate students working in ion chemistry and related fields and will be an invaluable reference for years to come. The contributions to the series embody the wealth of molecular information that can be obtained by studying chemical reactions between ions, electrons and neutrals in the gas phase. 

Thirdly, there is the purely structural argument from Relative Size if ions of one type are much the largest, they will effectively fix the structure since the others can pack between them. This argument, which makes no assumption whatever about electron-clouds, is often referred only to lithium iodide, but much more evidence is available. Such questions of crystal-form and isomorphism are in fact the most important applications of ionic-radius systems in chemistry and mineralogy (cp. the classical work of V. M. Goldschmidt (2)). 

In the 2-level limit a perturbative approach has been used in two famous problems the Marcus model in chemistry and the small polaron model in physics. Both models describe hopping of an electron that drags the polarization cloud that it is formed because of its electrostatic coupling to the enviromnent. This enviromnent is the solvent in the Marcus model and the crystal vibrations (phonons) in the small polaron problem. The details of the coupling and of the polarization are different in these problems, but the Hamiltonian formulation is very similar. ... 

There has been a great deal of research activity on the effects of subsonic aircraft in the upper troposphere, with respect to impacts both on the chemistry and on the radiation balance through effects on clouds and 03 (e.g., see April 15, May 1, and May 15, 1998, issues of Geophysical Research Letters and the July 27, 1998, issue of Atmospheric Environment). Aircraft emit a variety of pollutants, including NOx, S02, and particles whose concentrations have provided exhaust signatures in some studies (e.g., Schlager et al., 1997 Hofmann et al., 1998). 

Liang, J., and D. J. Jacob, Effect of Aqueous Phase Cloud Chemistry on Tropospheric Ozone, J. Geophys. Res., 102, 5993-6001 (1997). 

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