Stratospheric chemical

Why temperatures and rainfall near Chesapeake Bay should be affected by variations of the tidal forces is not so clear. However the atmosphere and stratosphere are pulled away from the earth by tidal forces just as are the waters of the earth. These forces vary by as much as 10 percent during the tidal periods [67] resulting in density variations in the stratosphere with the same periods the consequent density variations may affect the relative rates of stratospheric chemical reactions, causing disturbances of temperature and rainfall on the ground with the tidal periodicities. 

The model tropopause is defined by a PV level of 3.5 pvu poleward of 20° latitude, and by a -2 K km 1 temperature lapse rate equatorward of 20° latitude. Consequently, in this study the troposphere is defined as the volume between the surface and the simulated tropopause. Because the model does not consider typical stratospheric chemical reactions explicitly, ozone concentrations are prescribed from 1-2 levels above the model tropopause up to the top of the model domain at 10 hPa. In both hemispheres we apply monthly and zonally averaged distributions from a 2D stratospheric chemistry model [31]. In the present version of the model, we use the simulated PV and the regression analysis of the MOZAIC data (Section 2) to prescribe ozone in the NH extratropical lower stratosphere, which improves the representation of ozone distributions influenced by synoptic scale disturbances [32, 33]. Furthermore, the present model contains updated reaction rates and photodissociation data [34]. 

The basic scenarios examine some of the important aspects in understanding the calculated environmental impact of aircraft. However, a number of uncertainties remain in the treatment of chemical and physical processes that may influence the effects from aircraft emissions. A series of special sensitivity calculations were therefore designed to investigate the most important of the recognised uncertainties. The subsonic aircraft sensitivity scenarios, as described later, examine uncertainties in the background atmosphere, the treatment of upper tropospheric and lower stratospheric chemical and dynamical processes, and the different analyses of aircraft emissions. 

Abstract. The impact of future aircraft emissions on concentrations of reactive nitrogen, water vapour and ozone has been calculated using the 3-dimensional stratospheric chemical transport model SCTM-1. Emissions of NOx (N0+N02) and H20 from both sub- and supersonic aircraft have been considered. 

Figure 5.2. Stratospheric chemical cycle affecting odd oxygen species in the stratosphere. The numbers in boxes represent concentrations (cm-3) calculated at 25 km altitude while the numbers associated with the arrows account for the reaction fluxes (cm-3s-1) between different compounds (24 hour global average conditions). Note that the figure extends beyond the simple pure oxygen chemistry case and that NO2 is identified as an odd-oxygen reservoir. (See following sections for more details from Zellner, 1999).

Estimates for the atmospheric lifetime of N20 come from stratospheric chemical transport models that have been tested against observed N20 distributions. The best... 

A chemical mechanism is evaluated by comparing its predictions to laboratory or field data. Both the measurements and the predictions have uncertainties associated with them since the agreement between measurements and predictions is never perfect, the question then arises as to whether the differences exhibited are significant. When dealing with an atmospheric chemical mechanism, it is desirable to place uncertainty bounds on simulations. There have been a number of such studies for stratospheric chemical mechanisms (Stolarski et al., 1978 Falls et al., 1979 Ehhalt et al., 1979 Tilden et al., 1981 Tilden and Seinfeld, 1982 Stolarski and Douglass, 1986). 

Brasseur, G., Simon, P.C. Stratospheric chemical and thermal resprmse to long-term variability in solar uv irradiation. J. Geophys. Res. 86, 7343-7368 (1981)... 

In the mid-1970s, it was realized that the CFCs in widespread use because of their chemical inertness, would diffuse unaltered through the troposphere and into the mid-stratosphere where they, too, would be photolyzed by uv (<240 nm) radiation. For example, CFC-12 can photolyze ... 

T. E. Graedel, D. T. Hawkias, and L. D. CExton, Atmospheric Chemical Compounds Sources, Occurrence and Bioassay, Academic Press, New York, 1986. Atmospheric O ne 1985, World Meteorological Organization, Geneva, Switzerland (3 vols.) an excellent compendium on tropospheric and stratospheric processes. 

The key gas-phase reactions occurring in the stratosphere are generally known. Comprehensive reviews of kinetic data have led to general consensus on the rate parameters that should be used in stratospheric models (91). Nevertheless, discrepancies are stiU apparent when the chemical components of... 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

W. B. DeMore and co-workers. Chemical Kinetics and Photochemical Data for Use in Stratospheric Ocyone Modeling Evaluation No. 8, JPL Publ. 87—41, Jet Propulsion Laboratory, Pasadena, Calif., 1987. 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

What are the principal chemical reactions that take place in the chemosphere to give it its name How do they influence stratospheric and tropospheric chemical reactions ... 

Stratospheric ozone is in a dynamic equilibrium with a balance between the chemical processes of formation and destruchon. The primary components in this balance are ultraviolet (UV) solar radiation, oxygen molecules (O2), and oxygen atoms (O) and may be represented by the following reactions ... 

An important effect of air pollution on the atmosphere is change in spectral transmission. The spectral regions of greatest concern are the ultraviolet and the visible. Changes in ultraviolet radiation have demonstrable adverse effects e.g., a decrease in the stratospheric ozone layer permits harmful UV radiation to penetrate to the surface of the earth. Excessive exposure to UV radiation results in increases in skin cancer and cataracts. The worldwide effort to reduce the release of stratospheric ozone-depleting chemicals such as chlorofluorocarbons is directed toward reducing this increased risk of skin cancer and cataracts for future generations. 

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