Clouds, atmospheric chemistry

Sander, R. Modeling atmospheric chemistry Interactions between gas-phase species and liquid cloud/aerosol particles, Surv. Geophys., 20, 1-31, 1999. 

Atkinson, R., D. L. Baulch, R. A. Cox, R. F. Hampson, J. A. Kerr, M. J. Rossie, and J. Troe, Evaluated Kinetic and Photochemical Data for Atmospheric Chemistry. Supplement V. IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry, J. Phys. Chem. Ref. Data, 26, 521-1011 (1997). Bordewijk, J. A., H. Slaper, H. A. J. M. Reinen, and E. Schlamann, Total Solar Radiation and the Influence of Clouds and Aerosols on the Biologically Effective UV, Geophys. Res. Lett., 22, 2151-2154 (1995). 

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. 

Penner, J. E Cloud Albedo, Greenhouse Effects, Atmospheric Chemistry, and Climate Change, J. Air Waste Manage. Assoc., 40, 456-461 (1990). 

The FREZCHEM model can be used to simulate what would happen theoretically to cloud droplets and their chemistries as they are lofted (convected) to higher (colder) altitudes. We used two aqueous datasets to simulate atmospheric chemistries. The first dataset consist of mean annual concentrations of ions in precipitation from the Hubbard Brook ecosystem (1.0 km altitude) (table 4 in Likens et al. 1977). The second dataset is from Mt. Sonnblick, Austria (3.1km altitude) and is a direct measure of cloud chemistry (table II, May 1991 in Brantner et al. 1994). In both cases, the chemistries are similar in relative concentrations with H+, NHj, Na+, Cl-, NOg and SO4- as the dominant ions. 

Schwartz, S. E. Mass-transport considerations pertinent to aqueous-phase reactions of gases in liquid-water clouds. In Chemistry of Multiphase Atmospheric Systems Jaeschke, W.,... 

Several areas in which chemical measurement technologies have become available and/or refined for airborne applications have been reviewed in this paper. It is a selective review and many important meteorological and cloud physics measurement capabilities of relevance to atmospheric chemistry and acid deposition (e.g., measurement of cloud liquid water content) have been ignored. In particular, we have not discussed particle size spectra measurements for various atmospheric condensed phases (aerosols, cloud droplets and precipitation). Further improvements in chemical measurement technologies can be anticipated especially in the areas of free radicals, oxidants, organics, and S02 and N02 at very low levels. Nevertheless, major incremental improvements in the understanding of acid deposition processes can be anticipated from the continuing airborne application of the techniques described in this review. 

General References Crowl and Louvar, Chemical Process Safety Fundamentals with Applications, Prentice Hall, Englewood Cliffs, NJ, 1990, pp. 121-155. Hanna and Drivas, Guidelines for Use of Vapor Cloud Dispersion Models, AIChE, New York, 1987. Hanna and Strimaitis, Workbook of Test Cases for Vapor Cloud Source Dispersion Models, AIChE, New York, 1989. Lees, Loss Prevention in the Process Industries, Butterworths, London, 1986, pp. 428-463. Seinfeld, Atmospheric Chemistry and Physics of Air Pollution, Chaps. 12, 13, 14, Wiley, New York, 1986. Turner, Workbook of Atmospheric Dispersion Estimates, U.S. Department of Health, Education, and Welfare, Cincinnati, 1970. 

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... 

Figure 9 Volcanic clouds are typically composed of gases and particles and diluted by the background atmosphere. Various chemical and physical processes and transformations acting during plume transport further modify plume composition. The chemical and physical form of plume components, their spatial and temporal distribution, and their deposition are therefore strongly controlled by atmospheric chemistry and transport of the plume.

As a first step in assessing the potential importance of nanoparticle reactions, we compare the volume and surface areas of these particles with the same values from other condensed phases with known chemical effects. We first consider nanoparticle volumes. As an upper limit, we consider an urban air parcel containing 20-nm diameter nanoparticles at a number concentration of 10 cm. Under this scenario, the nanoparticle volume is a small fraction (10 of the total air parcel volume. Thus the nanoparticle reaction rate (in units of mol m -air s ) would have to be ca. 10 times as fast as the equivalent gas phase reaction (mol m -air s ) to have a comparable overall rate in the air parcel. For comparison, clouds typically have liquid water contents of 10 to 10 (volume fraction) and can have significant effects upon atmospheric chemistry (Seinfeld and Pandis 1998). For simplicity of argument, if the medium of the cloud droplets and nanoparticles are assumed similar (e.g., dilute aqueous), then the fundamental rate constants in each medium are similar. Under this condition, reactant concentrations in the nanoparticles would need to be enhanced by 10, as compared to the cloud droplets, to have equal rates. Based on this analysis, it appears unlikely that reactions occurring in the bulk of nanoparticles could affect the composition of the gas phase. 

Cox, R.A., Hewitt, C.N., Liss, P.S., Lovelock, J.E., Shine, K.R. Thrush, B.A. (eds) (1997) Atmospheric chemistry of sulphur in relation to aerosols, clouds and climate. Philosophical Transactions of the Royal Society of London 352B, 139-254. 

Atmospheric chemistry has not yet been fully understood. One of the main reasons is the complex interaction between components of the gas phase and of the condensed phases. In this contribution we would like to consider, by example of the reaction between aqueous SO2 and molecular oxygen, occurring in the presence of nitrate, some aspects of such an interaction which may be of interest both to the researchers and modellers of cloud chemistry. 

Nitrogen oxide, formed by photofragmentation of N02 or chlorine nitrate (C10N02), hydroxyl radicals and some other reactive species are also responsible for stratospheric ozone depletion. These compounds may have both natural and anthropogenic (combustion, etc.) origin. Atmospheric chemistry also takes place in aerosol particles, cloud droplets1370 and ice crystals.1371,1372... 

Atmospheric chemistry is dominated by trace species, ranging in mixing ratios (mole fractions) from a few parts per million, for methane in the troposphere and ozone in the stratosphere, to hundredths of parts per trillion, or less, for highly reactive species such as the hydroxyl radical. It is also surprising that atmospheric condensed-phase material plays very important roles in atmospheric chemistry, since there is relatively so little of it. Atmospheric condensed-phase volume to gas-phase volume ratios range from about 3 x KT7 for tropospheric clouds to 3 x ICE14 for background stratospheric sulfate aerosol. 

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