Aircraft stratospheric measurements

The Airborne Submillimeter SIS Radiometer (ASUR), operated on-board the German research aircraft FALCON, measures thermal emission lines of stratospheric trace gases at submillimeter wavelength. Measurement campaigns with respect to ozone depletion in the Arctic winter stratosphere were carried out in yearly intervals from 1992-97 to investigate the distributions of the radical chlorine monoxide (CIO), the reservoir species hydrochloric acid (HC1), the chemically inert tracer nitrous oxide (N20), and ozone (O3). The high sensitivity of the receiver allowed to take spatially well resolved measurements inside, at the edge, and outside of the Arctic polar vortex. This paper focuses on the results obtained for CIO from... 

Wennberg et al. (1994) reported a comprehensive lower stratospheric in situ measurement campaign, carried out in May 1993, which, for the first time, included simultaneous measurements of OH, HOj, NO, CIO, and BrO, species. The aircraft-based measurements were carried out in the altitude range between 16 and 20 km. Production of O3 by reaction... 

The discovery of ozone holes over Antarctica in the mid-1980s was strong observational evidence to support the Rowland and Molina hypothesis. The atmosphere over the south pole is complex because of the long periods of total darkness and sunlight and the presence of a polar vortex and polar stratospheric clouds. However, researchers have found evidence to support the role of CIO in the rapid depletion of stratospheric ozone over the south pole. Figure 11-3 shows the profile of ozone and CIO measured at an altitude of 18 km on an aircraft flight from southern Chile toward the south pole on September 21, 1987. One month earlier the ozone levels were fairly uniform around 2 ppm (vol). 

Fig. 11-3. Stratospheric ozone and CIO concentrations at an altitude of 18 km measured by aircraft flying south over Antarctica on September 27,1987. The dramatic decrease in ozone at a latitude of 71 degrees is attributed to the role of CIO in catalytic destruction of ozone. Adapted from Anderson et al. (13).

Water vapor concentrations have also been used to show that stratospheric air in the midlatitudes cannot all have originated via the tropical pump, i.e., path I in Fig. 12.3. For example, Dessler et al. (1995b) have shown that water vapor concentrations in the lowermost stratosphere at 37.4°N, 122.1°W are higher than expected for an air mass that has passed through the cold tropical tropopause. Their data are consistent with path II, although as they point out, these measurements do not exclude path III, which represents convective transport from the troposphere to the stratosphere at mid and high latitudes. Lelieveld et al. (1997) report aircraft measurements of CO, 03, and HNO-, over western Europe that suggest that tropospheric air can be mixed into the lower stratosphere. 

Figure 24-19 Partial gas chromatogram for which an electron capture detector was used to measure halogenated compounds in air collected by an aircraft at an altitude of 800 m at a location 1 400 km south of New Zealand in 1995. /From F. S. Howland, Stratospheric Ozone Depletion by Chloroftuorocarbons." Angtyw Chem. Int. Bd. Engl. 1996,35, 1787]...

Figure 2. The temperature and pressure distribution of the stratosphere. The solid line is from reference 7, and the dashed lines are from measurements made by the Meteorological Measurement System (MMS) instrument on the NASA ER-2 high-altitude aircraft during the AAOE mission in 1987 (8) and the AASE mission in 1989 (9). The Arctic was colder in 1989 than usual.

Aircraft measurements of CIO and BrO are discussed in some detail in the next section. Because the aircraft and balloon-borne techniques are essentially the same, further discussion about these two reactive trace gases is deferred to this later section. A discussion of some of the challenges of measuring atomic trace gases in the stratosphere follows. 

It is difficult to envision that balloon-borne techniques will be able to satisfy the demand for more complex and frequent measurements. Therefore it is critical for maximizing the scientific return of balloon-borne flights to include simultaneous measurements of the right mix of species and photolysis rates. In the absence of frequent balloon-borne measurements it is nonetheless very gratifying to have achieved the coalescence of results by independent techniques as a zero-order substitute for intercomparisons. A possible direction for future stratospheric research with a new platform, remotely piloted aircraft, that alleviates some disadvantages of balloon-borne platforms is discussed in the last section of this chapter. 

In Situ Measurements Balloons. Balloons currently provide the only in situ platform that allows access to the upper part of the stratosphere (above 20 km). The engineering requirements are similar to those for aircraft except for a more relaxed time response. Regional coverage from balloons is difficult, particularly because the launching facilities for the large stratospheric balloons are very limited and generally localized in the midlatitudes. However, vertical profiles without horizontal distortion are the natural data collection mode. Measurement contamination due to emissions from the balloon is a potential problem. 

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). 

Tuck A.F. et al.(1997) Airborne Southern Hemisphere Ozone Experiment/ Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/ MAESA) A road map, J. Geophys. Res., 102. 

Passive remote sensing by mid-infrared spectroscopy has been successfully applied to the measurement of a large number of stratospheric trace constituents and some upper tropospheric constituents. Initially measurements were made from mountain tops (e.g. Zander, 1981), and balloon and aircraft experiments were subsequently developed (Fischer et al., 1980 Murcray et al., 1975 1979 Coffey et al., 1981 Brasunas etal., 1988 Kunde etal., 1988). 

Will you please give us some details about how you make the sampling. Since most measurements are made in the stratosphere, I presume this has been done by aircraft. Now, and since you have been using as experimental device a mass spectrometer, how are you able to make a distinction between ions and molecules And the second question if the species you describe in your slides have been really shown, in other words have been experimentally demonstrated with this pathway which you assume that the ions are recombined. 

Stratospheric sulfate and other gases were collected by high altitude aircraft and balloons (Gandrud et d., 1983 Mroz et d., 1983 Vedder et d., 1983). These measurements indicated an injection of about 7.6 Tg of sulfate into the global stratosphere. Ground and airborne extinction measurements were also carried out (Clarke et d., 1983 Coulson, 1983 Dutton and De Luisi, 1983 Spinhirne, 1983 Witteborn et d., 1983) as well as comparisons with Lidar measurements (Swissler et d., 1983). Other reports on the initial phases of this phenomenon and attempts at drawing preliminary conclusions have by now appeared some will be mentioned in the following section. 

Gandrud B.W., Kritz M.A. and Lazrus A.L., Balloon and aircraft measurements of stratospheric sulfate mixing ratio following the El Chichon eruption. Geophys. Res. Lett. , 10, 1037-1040 (1983). 

According to aircraft measurements within the USSR, the plume height exceeded 1200 m on 27 April and on subsequent days, the plume height did not exceed 200-400 m. The volatile elements iodine and caesium, were detectable at greater altitudes (6-9 km), with traces also in the lower stratosphere (Jaworowski et al., 1988). The refractory elements, such as cerium, zirconium, neptunium and strontium, were for the most part of significance only in local deposition within the USSR. 

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