Radiative activity

Tropospheric ozone is also radiatively active and there is good evidence that it is now about twice its pre-industrial concentration, at least in the northern hemisphere. This increase is due to... 

Concern has been expressed over the destruction of ozone in the stratosphere brought about by its reactions with chlorine atoms produced from chlorofluoroalkanes that are persistent in the troposphere, and that may contribute to radiatively active gases other than COj. 

Nouchi I, Mariko S. Mechanisms of methane transport by rice plants. In Oremland RS, editor. Biogeochemistry of Global Change Radiatively Active Trace Gases. New York Chapman Hall 1993. pp. 336-352. 

Chemical vapor deposition (CVD) is a process whereby a thin solid film is synthesized from the gaseous phase by a chemical reaction. It is this reactive process that distinguishes CVD from physical deposition processes, such as evaporation, sputtering, and sublimation.8 This process is well known and is used to generate inorganic thin films of high purity and quality as well as form polyimides by a step-polymerization process.9-11 Vapor deposition polymerization (VDP) is the method in which the chemical reaction in question is the polymerization of a reactive species generated in the gas phase by thermal (or radiative) activation. 

Conrad R. 1993. Mechanisms controlling methane emission from wetland rice fields. In Oremland R, ed. Biogeochemistry of Global Change. Radiatively Active Gases. New York Chapman HaU, 317-355. 

Simmonds, P. G., R. G. Derwent, A McCulloch, S. O Doherty, and A. Gaudry, Long-Term Trends in Concentrations of Halocar-bons and Radiatively Active Trace Gases in Atlantic and European Air Masses Monitored at Mace Head, Ireland from 1987-1994, Atmos. Environ., 30, 4041-4063 (1996). 

The Ta <— So transition moments to particular spin sublevels for the three lowest triplet states of the ozone molecule, 3B2,3 A2 and 3B, were calculated by the MCQR method in ref. [70] using CASSCF wave functions. Table 7 recapitulates results for electric dipole radiative activity of different S-T transitions in ozone [70]. The type of information gained form this kind of spin-orbit response calculations are viz. transition electric dipole moments and oscillator strengths for each spin sublevel T , their polarization directions (7), radiative lifetimes (r ) and excitation energies (En). The most prominent features of the Chappuis band are reproduced in calculations, which simulate the photodynamics of ozone visible absorption [78, 79]. Because the CM (M2) state cannot be responsible for the Wulf bands, the only other candidates ought to... 

Vibrational analysis of the benzene phosphorescence bands indicates that the radiative activity is induced predominantly by e2g vibrations [155, 156]. A weak but observable activity of b2g vibrations has also been found [156, 155, 157]. By introducing spin-orbit- and vibronic coupling through second order perturbation theory Albrecht [158] showed that the vibronic interaction within the triplet manifold is responsible for the larger part of the phosphorescence intensity. This also follows from comparison of the vibrational structure in phosphorescence and fluorescence spectra [159]. The benzene phosphorescence spectrum in rigid glasses [155] reveals a dominant vibronic activity of... 

Recent Anthropogenic Changes in Carbon Dioxide and Other Radiatively Active Gases... 

In the lower atmosphere (i.e. the troposphere and stratosphere) N2 is not radiatively active, whereas in heights above 100 km (i.e. in thermosphere) N2 absorbs at wavelengths less than 100 nm (Graedel and Crutzen, 1993). 

Cynar F. J. and Yayanos A. A. (1993) The oceanic distribution of methane and its flux to the atmosphere over Southern California waters. In Biogeochemistry of Global Change Radiatively Active Trace Gases (ed. R. S. Oremland). Chapman and Hall, New York, pp. 551-573. 

In Section 4.6.4, the role of CFCs in stratospheric ozone destruction was discussed. CFCs also are of concern because they are radiatively active in portions of the infrared spectrum not strongly attenuated by water vapor, C02, CH4, or N20. Currently, a CFC molecule added to the atmosphere absorbs about 10,000 times as much long-wave infrared radiation as does a C02 molecule. C02 has a radiative forcing of 1.8 X 10-5 W/(m2 ppb(v)), whereas CFCs range from 0.22 to 0.32 W/(m2 ppb(v)) (Prather et al., 1996). CFCs also have long atmospheric residence times, ranging from 50 to 1700 years. The locations of some CFC absorbance bands are shown in Fig. 4-42. Unlike the several radiatively active trace gases that have both natural and... 

The radiatively active trace gases, which contribute most to atmospheric absorption, and hence play a key role in the energy budget of the middle atmosphere, are carbon dioxide, ozone, and water vapor. Other gases, whose sources are partly related to anthropogenic activity (such as CH4, N2O, and chlorofluorocarbons) also contribute to the radiation budget. 

Figure 4-21. Spectral distribution of the absorption by several radiatively active gases (from the Earth s surface to infinity). The aggregate spectrum due to all atmospheric gases is shown in the bottom panel (adapted from Shaw, 1953).

By measuring the spectral distribution of the upwelling infrared radiation emitted by the Earth and its atmosphere, spaceborne sensors can provide information on the vertical temperature profile and on the atmospheric abundance of radiatively active trace gases. When local thermodynamic equilibrium conditions apply, the radiance received by a detector with spectral response function y> over frequency interval Av and viewing vertically downwards is given by (see Eq. 4.69a)... 

The previous discussion is based on the assumption that collisional excitation and de-excitation is the dominant process determining the populations of the vibrational-rotational levels of all radiatively active molecules. This is usually the case in the lower atmosphere, where the pressure is high and molecular collisions are frequent. The relative populations of the upper and lower states of a vibrational-rotational transition are then described by the Boltzmann distribution at the local kinetic temperature T, the gas is considered to be in local thermodynamic equilibrium (LTE), and Kirchoff s law can be applied locally. If we consider a two-level system, then the relative populations of the lower and upper states, no and ni, respectively, are given by... 

Radiatively active gases, including CO2, CH4, N,0, CFCs, and O3, contribute to the so-called greenhouse effect of the atmosphere, and the observed perturbations in their atmospheric concentrations have led to significant climate forcing. For the period 1850-2000, this forcing is estimated to be around 2.5 W m -(IPCC, 1996). 

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