Aerosol in the stratosphere

Actually measuring the composition and phase of PSCs and aerosols in the stratosphere is extremely difficult. Some direct measurements have been made by collecting aerosol samples and subsequently analyzing them using techniques such as X-ray energy-disper-... 

Following near-ground explosions, iodine isotopes are concentrated in the smaller particles, but H-tests at high altitude produce very small particles, which equilibrate with other aerosols in the stratosphere, and there is little fractionation. After the Chinese test of 15.10.80, high... 

As is mentioned in Sect. 2.2, a discussion of de-ionization processes in the Earth s atmosphere would be incomplete without a mention of the r le of aerosols. The attachment of ions to aerosols in the stratosphere and troposphere has been considered by several workers213. It is clear that their presence will enhance the loss of ions from the gas phase at a rate dependent on the nature, size and number density of the particles, and so this process, which could be the dominant ionization loss process, must be considered along with gas phase ionic recombination in detailed atmospheric de-ionization rate calculations. 

As the residence time of aerosols in the stratosphere is 2 yr and in the troposphere 1 week, the Be/ Be ratio of the two air masses is distinctive. Tropospheric air shows the ratio of Be relative to Be of 1.8, whereas stratospheric air has a ratio of 0.13. It is therefore possible to distinguish stratospheric air injected into the troposphere by considering the ratio of Be/ Be. Of course, the stratospheric air will also be higher in Be than the tropospheric air. As stratospheric air will also contain ozone, the interest in this source has been strong to distinguish from pollution-based tropospheric ozone. 

Worldwide enhancements of aerosols in the stratosphere are observed after big volcanic eruptions (i.e., by the volcano Pinatubo in 1991), which led to a decrease in direct solar irradiance and an increase in diffuse irradiance. This effect could be measured especially well at a high mountain station, where the disturbance by urban aerosol pollution is very small. In this case, diffuse solar radiation was increased nearly twofold, while global (direct and diffuse) radiation was reduced by about 4% [34]. 

Martell, E. A., 1966 The size distribution and interaction of radioactive and natural aerosols in the stratosphere. Tellus 18, 486-498. 

E. A. Martell. The Size Distribution and Interaction of Radioactive and Natural Aerosols in the Stratosphere, Tellus XVIII 486 (1965). 

Stratospheric Sulfur Aerosols. Stratospheric sulfur aerosols are minute sulfur-rich particles that are found in the Earth s stratosphere and are often observed following significant volcanic activity (such as after the 1991 Mount Pinatubo eruption). The presence of these aerosols in the stratosphere results in a cooling effect. The SRM geoengineering technique of intentionally releasing sulfur aerosols into the stratosphere is based on the concept that they... 

The uptake coefficient for HNO3 on soot appears to be y 0.15. Using a stratospheric surface area of 4 x 10 cm /cm (about one and a half orders of magnitude smaller than sulfate aerosol in the stratosphere) leads to a loss rate that competes with photolysis and reaction with OH in the daytime and which should be larger at night. 

Measurements of ozone concentration in the ozone layer in the stratosphere are made in the less intense Huggins band to avoid complete absorption of the laser radiation. Again, the two or three wavelength DIAL method is used to make allowance for background aerosol scattering. A suitable laser for these measurements is the XeCl pulsed excimer laser (see Section 9.2.8) with a wavelength of 308 nm, close to the peak absorption of the Huggins... 

A smaller factor in ozone depletion is the rising levels of N2O in the atmosphere from combustion and the use of nitrogen-rich fertilizers, since they ate the sources of NO in the stratosphere that can destroy ozone catalyticaHy. Another concern in the depletion of ozone layer, under study by the National Aeronautics and Space Administration (NASA), is a proposed fleet of supersonic aircraft that can inject additional nitrogen oxides, as weU as sulfur dioxide and moisture, into the stratosphere via their exhaust gases (155). Although sulfate aerosols can suppress the amount of nitrogen oxides in the stratosphere... 

The resultant O3 layer is critically important to life on Earth as a shield against LTV radiation. It also is responsible for the thermal structure of the upper atmosphere and controls the lifetime of materials in the stratosphere. Many substances that are short-lived in the troposphere (e.g. aerosol particles) have lifetimes of a year or more in the stratosphere due to the near-zero removal by precipitation and the presence of the permanent thermal inversion and lack of vertical mixing that it causes. 

A typical example of the interaction between hypothesis and experiment is the story of the work that resulted in worldwide concern over the depletion of the ozone layer in the stratosphere. These studies led to the awarding of the 1995 Nobel Prize for Chemistry to Paul Crutzen, Mario Molina, and F. Sherwood Rowland. Figure FT provides a schematic view of how this prize-winning research advanced. It began in 1971 when experiments revealed that chlorofluorocarbons, or CFCs, had appeared in the Earth s atmosphere. At the time, these CFCs were widely used as refrigerants and as aerosol propellants. Rowland wondered what eventually would happen to these gaseous compounds. He carried out a theoretical analysis, from which he concluded that CFCs are very durable and could persist in the atmosphere for many years. 

Ban on chlorofluorocarbons (CFCs) as aerosol propellants react with ozone in the stratosphere, causing an increase in the penetration of ultraviolet sunhght and increase the risk of skin cancer. 

Figure 3.25 shows the results of one set of calculations of the effects of aerosol particles whose properties were judged to be characteristic of continental or urban situations, respectively, on the transmission of UV and visible radiation to the earth s surface (Erlick and Frederick, 1998). The ratio of the transmission with particles to that without is plotted in two wavelength regions, one in the UV and one in the visible. Two different relative humidity scenarios are shown. The average summer relative humidity was 70% RH in the boundary layer and 20% RH in the free troposphere. The high relative humidity case assumes 90% RH in the boundary layer and 30% in the free troposphere. (The RH in the stratosphere was taken to be 0% in both cases see Chapter 12.)... 

Figure 3.32 shows some calculated actinic fluxes in the stratosphere at 20-, 30-, 40-, and 50-km altitude at a solar zenith angle of 30° (DeMore et al., 1997) as well as at ground level. The surface albedo was assumed to be 0.3 and the aerosol concentrations typical of moderate volcanic conditions. ... 

HC1 is efficiently absorbed into H2S04-H20 and into HN03-H2S04-H20 solutions, which as discussed earlier, are found in the stratosphere in the form of aerosol particles and Type I PSCs under some conditions (Wolff and Mulvaney, 1991). The solubility of HC1 in these liquid solutions can be expressed in terms of the usual Henry s law constant (Elrod et al., 1995 Abbatt, 1995 Luo et al., 1995 Hanson, 1998). Table 12.4 shows some typical measurements of the Henry s law constants for HC1 in several typical binary and ternary solutions, respectively. Hanson (1998) has shown that the solubility data for HC1 in binary mixtures of H2S04 and water in these and other studies can be fit by the form... 

There are a number of measurements documenting changes in NO and NO. in the stratosphere after the Mount Pinatubo eruption and which have been attributed to the removal of oxides of nitrogen due to reactions on aerosol particles. For example, a decrease in stratospheric NOz after the eruption followed by a return to normal levels has been reported (e.g., see Van Roozendael et al., 1997 and De Maziere et al., 1998). Similarly, NO decreases of up to 70% were reported, as well as increases in gaseous HN03 (much of that produced on the sulfate particles is released to the gas phase) (e.g., see Coffey and Mankin, 1993 Koike et al., 1993, 1994 David et al., 1994 Webster et al., 1994 and Rinsland et al., 1994). 

Brogniez, C J. Lenoble, R. Ramananaherisoa, K. H. Fricke, E. P. Shettle, K. W. Hoppel, R. M. Bevilacqua, J. S. Hornstein, J. Lumpe, M. D. Fromm, and S. S. Krigman, Second European Stratospheric Arctic and Midlatitude Experiment Campaign Correlative Measurements of Aerosol in the Northern Polar Atmosphere, J. Geophys. Res., 102, 1489-1494 (1997). 

Hamill, P., A. Tabazadeh, S. Kinne, O. B. Toon, and R. P. Turco, On the Growth of Ternary System HN03/H2S04/H20 Aerosol Particles in the Stratosphere, Geophys. Res. Lett., 23, 753-756 (1996). 

Hofmann, D. J., Increase in the Stratospheric Background Sulfuric Acid Aerosol Mass in the Past 10 Years, Science, 248, 996-1000 (1990). 

Jaegle, L., Y. L. Yung, G. C. Toon, B. Sen, and J.-F. Blavier, Balloon Observations of Organic and Inorganic Chlorine in the Stratosphere The Role of HCI04 Production on Sulfate Aerosols, Geophys. Res. Lett., 23, 1749-1752 (1996). 

Pueschel, R. F., D. F. Blake, K. G. Snetsinger, A. D. A. Hansen, S. Verma, and K. Kato, Black Carbon (Soot) Aerosol in the Lower Stratosphere and Upper Troposphere, Geophys. Res. Lett., 19, 1659-1662 (1992a). 

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