Stratosphere range

The air pressure in the stratosphere ranges from 100 mbar near 15 km to 0.1 mbar near 50 km, falling off exponentially with altitude as shown in Figure 2 (9). As in the troposphere, altitude and pressure are used as vertical... 

Figure 5.24 shows a distribution of stratospheric aerosol surface area as a function of altitude from 18 to 30 km inferred from satellite measurements. The surface area units used in Figure 5.24 are cm2 cm 3, and typical values of the stratospheric surface area at, say, 18 km altitude are about 0.8 x 10-8 cm2 cm-3. This is equivalent to 0.8pm2 cm 3. As a useful rule of thumb, stratospheric aerosol surface area in the lower stratosphere ranges between 0.5 and 1.0 pm2 cm-3. 

More complex ions are created lower in the atmosphere. Almost all ions below 70-80 km are cluster ions. Below this altitude range free electrons disappear and negative ions fonn. Tln-ee-body reactions become important. Even though the complexity of the ions increases, the detemiination of the final species follows a rather simple scheme. For positive ions, fomiation of H (H20) is rapid, occurring in times of the order of milliseconds or shorter in the stratosphere and troposphere. After fomiation of H (H20), the chemistry involves reaction with species that have a higher proton affinity than that of H2O. The resulting species can be... 

The turnover time of water vapor in the atmosphere obviously is a function of latitude and altitude. In the equatorial regions, its turnover time in the atmosphere is a few days, while water in the stratosphere has a turnover time of one year or more. Table 7-1 Qunge, 1963) provides an estimate of the average residence time for water vapor for various latitude ranges in the troposphere. Given this simple picture of vertical structure, motion, transport, and diffusion, we can proceed to examine the behavior of... 

H2O as the most variable of the dominant species. In Table 7-2, we deliberately omitted water because of its variability. It can range from ppmv levels in the Antarctic and the stratosphere to several percent in moist tropical air. Thus, it is necessary to reference the concentrations in the... 

Even with our much-advanced understanding of the chemistry of the stratosphere, it appears that there are still some discrepancies between the calculated amount of ozone in the stratosphere and the amount measured. Toumi and Kerridge have summarized data showing that the range of calculated concentrations is some 10-15% below the range of measured... 

CFCs. All "nonessential" uses of CFCs in aerosol propellents were banned in 1978—the first and only major control action under TSCA not specifically mandated by the statute. This action may have helped to reduce the future incidence of skin cancer by diminishing CFCs destructive effects on stratospheric ozone. Making appropriate assumptions about rates of ozone depletion and extrapolating from current disease rates, one could estimate a range of cancers avoided because of this prohibition. However, any health benefit due to the ban on aerosol CFC uses may be masked by the continued increase in non-aerosol uses. 

By using the 110, and NO, cycles just discussed and by assuming a NO concentration of 4.2 X 109 molecules/cm3 distributed uniformly through the stratosphere, Johnston and Whitten [119] were able to make the most reasonable prediction of the ozone balance in the stratosphere. Measurements of the concentration of NO in the stratosphere show a range of 2- 8 X 109 molecules/cm3. 

The 8 N- and 8 0-values of atmospheric N2O today, range from 6.4 to 7.0%c and 43 to 45.5%c (Sowers 2001). Terrestrial emissions have generally lower 8-values than marine sources. The 8 N and 8 0-values of stratospheric N2O gradually increase with altitude due to preferential photodissociation of the lighter isotopes (Rahn and Wahlen 1997). Oxygen isotope values of atmospheric nitrous oxide exhibit a mass-independent component (Cliff and Thiemens 1997 Clifif et al. 1999), which increases with altitude and distance from the source. The responsible process has not been discovered so far. First isotope measurements of N2O from the Vostok ice core by Sowers (2001) indicate large and 0 variations with time (8 N from 10 to 25%c and 8 0 from 30 to 50%c), which have been interpreted to result from in situ N2O production via nitrification. 

Troposphere is used here to represent the lowest layer of the atmosphere, ranging from the ground to the base of the stratosphere at 10—15 km altitude. Essentially, all data on particulate organic matter is from near ground level in the lower troposphere. 

Long-range effects of having less ozone in the stratosphere involve greater ultraviolet sunlight transmission, alteration of weather, and an increased risk of skin cancer. The ozone depletion potential for CFCs and other fluorocarbons have been measured and are given below relative to CFC-11 and -12. Notice that the HCFCs with lower chlorine content have lower depletion potentials than the CFCs, and the one HFC studied shows no depletion potential because it contains no chlorine. 

The concentration of ozone near the Earth s surface is very low, typically in the range of 15-45 pphv (parts per billion by volume). In contrast, ozone is more abundant in the Earth s stratosphere, where it is formed by the action of ultraviolet radiation on molecules of dioxygen. A distinction is sometimes made between stratospheric ozone ("good ozone") and tropospheric (low-level or surface ozone "bad ozone"). This distinction arises from the fact that stratospheric ozone reduces the amount of ultraviolet radiation that reaches the Earth, reducing the rate of skin cancer and other medical problems... 

Destruction of stratospheric ozone caused by relatively small atmospheric concentrations of chlorofluo-rocarbons has vividly illustrated the capacity of human activity to alter our atmosphere in a manner that has significant and far-ranging effects. There is similar concern for the effects of greenhouse gases on the earth s climate. 

Many addition reactions such as the OH-SOz reaction are in the falloff region between second and third order in the range of total pressures encountered from the troposphere through the stratosphere. Troe and co-workers have carried out extensive theoretical studies of addition reactions and their reverse unimolecular decompositions as a function of pressure (e.g., see Troe, 1979, 1983). In this work they have developed expressions for the rate constants in the falloff region these are now most commonly used to derive the... 

---