Stratosphere defined

Because of the strong absorption of ultraviolet (UV) radiation starting at 320 nm by 03, one of the major impacts of decreased stratospheric ozone is expected to be increased UV at the earth s surface, with associated effects such as increases in skin cancer and cataracts and damage to plants and other ecosystem components. It has therefore been of great interest to determine whether such a relationship can be detected and, if so, what the magnitude of the effect is. The latter is commonly expressed as an amplification factor (AF) or radiation amplification factor (RAF), defined as the fractional change in radiation (R) per fractional change in total column ozone (03) ... 

Tihe atmosphere contains many radionuclides which result from nuclear weapons testing and from natural processes. The nuclear weapons-produced radionuclides include both fission products and activation products from the construction materials of the device. The natural radionuclides include the decay products of radon and thoron, the natural radionuclides in the airborne dust, and the cosmic-ray-produced radionuclides which result from spallation reactions in the atmosphere. Through the determination of the absolute and relative concentrations of this wide spectrum of radionuclides, it should be possible to define the rates of both the long term stratospheric processes and the shorter term tropospheric processes. At the beginning of 1962 a ground-level... 

Atmospheric column absorption measurements from the surface are possible for NO, N02, NOi3, HNOi3, and C10N02 (23-25). These measurements have defined the seasonal cycle (25) as well as much more rapid variations (26) in the stratospheric levels of N03. Under favorable conditions these measurements can yield information concerning the vertical profiles of the measured species (24, 26). Such techniques can also be used from aircraft platforms (27, 28). 

For the discussion of the formation and destruction of ozone in (In stratosphere it is convenient to define the photodissociation coefficient generally denoted by J (in units ofsec 1). J is the probability of dissocial mn of a molecule per second by light absorption. 

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]. 

Leung, Colussi and Hoffmann have used isotopic analysis in an attempt to constrain the amount of sulfate that could be produced by Crutzen s mechanism [129,130]. The first study retrieved the concentration profiles of OC S and OC S from infrared transmission spectra of the atmosphere recorded by the NASA MkIV balloon-borne interferometer. They derived an enrichment factor of 73.8 zb 8.67oo defined such that photolytically generated sulfur would be enriched in An isotopic budget based on this result shows that OCS photolysis cannot be a significant source of sulfate aerosol, since the enrichments of OCS, sulfuric acid aerosol and SO2 are known to be small [131]. A later laboratory study by the same group came to the conclusion that stratospheric photolysis results in an enrichment of 67 zb 77oo. 

The major advantage of these agents is that they become gaseous at well-defined temperatures and controlled rates, providing product quality and contributing to some improved performance characteristics. However, the effect of CFCs on the environment is under debate. These liquids, odorless and innocuous as they are, are linked to the ozone hole in the stratosphere. The industry is searching for feasible, environmentally and economically acceptable alternatives. Production levels of CFCs have been frozen and gradual phase-out is underway (8). 

The boundaries between atmospheric layers are not rigidly fixed for example, the boundary between the troposphere and the stratosphere varies from an average of about 7,500 m (25,000 ft) near the poles to 17,000 m (55,000 ft) near the equator, and fluctuates seasonally. A reference profile, the Standard Atmosphere, is defined by the International Civil Aviation Organization to represent typical atmospheric conditions at midlatitudes (Table 4-1). At sea level, the Standard Atmosphere exerts a pressure of 760 mm of mercury (1 atm) and has a temperature of 15°C (59°F). (Note that English units are still in widespread use in the meteorology and aviation communities in the United States.) Pressure decreases approximately exponentially with increasing altitude at 5500 m (18,000 ft), pressure is half that at sea level. 

Chlorine or other halogen bearing hydrocarbons (typically chlorofluorocarbons) defined as either class 1 or class 2 substances comprise the major stratospheric ozone depleting substances. EPA has established a midterm objective of an atmospheric chlorine content <2 parts per billion (ppb). 

In this book air chemistry is defined as a branch of atmospheric science dealing with the atmospheric part of the biogeochemical cycle of different constituents. In other words this means that we will deal mainly with the atmospheric pathways of those components that are involved in the mass flow between the atmosphere and biosphere, as well as in chemical interactions between the air and the other media of our environment (soils, oceans etc.). It follows from this definition that, on the one hand, our discussion will be restricted to the troposphere and the stratosphere4 and, on the other hand, the photochemistry of the upper layers, the subject matter of the aeronomy (e.g. Nicolet, 1964), will be omitted. This separation of the (photo) chemistry of the lower (troposphere and stratosphere) and upper atmosphere makes it possible to give a more compact treatment of our problem, including the global anthropogenic effects due to the increase of air pollution. 

---