Cloud surface chemistry

Poschl, U., Rudich, Y., and Ammann, M. (2005) Kinetic model framework for aerosol and cloud surface chemistry and gas-particle interactions Part 1—general equations, parameters, and terminology, Atmos. Chem. Phys. Discuss. 5, 2111-2191. 

Unlike melting and the solid-solid phase transitions discussed in the next section, these phase changes are not reversible processes they occur because the crystal stmcture of the nanocrystal is metastable. For example, titania made in the nanophase always adopts the anatase stmcture. At higher temperatures the material spontaneously transfonns to the mtile bulk stable phase [211, 212 and 213]. The role of grain size in these metastable-stable transitions is not well established the issue is complicated by the fact that the transition is accompanied by grain growth which clouds the inteiyDretation of size-dependent data [214, 215 and 216]. In situ TEM studies, however, indicate that the surface chemistry of the nanocrystals play a cmcial role in the transition temperatures [217, 218]. 

The term "heterogeneous" as applied to the atmosphere refers to chemistry that occurs in or on ambient condensed phases that are in contact with the gas phase aerosols, clouds, surface waters, etc. It is important to distinguish between heterogeneous processes that occur on the surface of the solid, and multiphase chemical reactions that take place in the bulk of the liquid medium. In the latter case, it is assumed that the reaction takes place after the molecule has been incorporated in the bulk liquid medium, such as occurs by wet deposition, where a species is ultimately removed from the atmosphere, especially in the troposphere. 

Ion-molecule reactions in interstellar clouds Radiation chemistry in interstellar grain mantles Condensation in stellar outflows Equilibrium reactions in the solar nebula Surface catalysis (Fischer-Tropsch) in the solar nebula Kinetically controlled reactions in the solar nebula Radiation chemistry (Miller-Urey) in the nebula Photochemistry in nebular surface regions Liquid-phase reactions on parent asteroid Surface catalysis (Fischer-Tropsch) on asteroid Radiation chemistry (Miller-Urey) in asteroid atmosphere... 

Langmuir, Irving (1881-1957). Fundamental research on surface chemistry, monomolecular films, emulsion chemistry. Also electric discharges in gases, cloud seeding, etc. Nobel Prize 1932. 

The existence of aerosol surfaces in the stratosphere has been known for many decades, but it was not until the discovery of the Antarctic ozone hole that their role in surface chemistry was recognized. Here the stratospheric sulfate layer and polar stratospheric clouds will be... 

Other species which do not take part in the surface chemistry can also show enhancement with respect to their observed abundances in cold clouds. This is because their abundances, which are known from chemical models to show a peak at around 10 years, are effectively "frozen" by the molecules accreting onto the dust, and later being released. This may be the case for methanol, CH30H, which is overabundant in hot cores (Menten et al. 1986). 

Chang Q, Cuppen HM, Herbst E. (2007) Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry. A.itron. Astrophys. 469 973-983. 

Perxanthate ion may also be implicated [59]. Even today, the exact nature of the surface reaction is clouded [59, 79-81], although Gaudin [82] notes that the role of oxygen is very determinative in the chemistry of the mineral-collector interaction. 

The total wet deposition flux consists of 2 contributory factors. The first derives from the continuous transfer of Hg to cloud water, described by chemistry models. There are 2 limiting factors 1) the uptake of gas phase Hg(0), which is regulated by the Hemy s corrstant and 2) the subsequent oxidation of Hg(0) to Hg(ll), which is governed by reaction rate constants and the irritial concentratiorrs of the oxidant species. The total flirx depends on the hquid water content of the cloud and the percentage of the droplets in the cloud that reach the Earth s surface. 

The cocktail of molecules, however, depends on the composition and condition of the cloud and the allowed chemistry on the surface or within the ice mantle. A complex network of chemical reactions exists, taking in energy from the... 

Particles in the accumulation range tend to represent only a small portion of the total particle number (e.g., 5%) but a significant portion (e.g., 50%) of the aerosol mass. Because they are too small to settle out rapidly (see later), they are removed by incorporation into cloud droplets followed by rainout, or by washout during precipitation. Alternatively, they may be carried to surfaces by eddy diffusion and advection and undergo dry deposition. As a result, they have much longer lifetimes than coarse particles. This long lifetime, combined with their effects on visibility, cloud formation, and health, makes them of great importance in atmospheric chemistry. 

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