Simultaneous measurements, stratosphere

In situ measurements of stratospheric reactive trace gas abundances provide an opportunity to test the fundamental photochemical mechanisms (3). The advantage of such measurements is that they are local, so the simultaneous measurements of trace gases place a true constraint on the possible photochemical mechanisms. These measurements are also able to resolve small-scale spatial and temporal structure in the trace constituent fields. The disadvantage of in situ measurements is that they do not capture the global or perhaps even seasonal view of photochemical transformations because they are seldom done frequently enough or in enough places to provide that information. Another disadvantage of in situ measurements is that they must be made from platforms in the stratosphere, and these remote observational outposts have their liabilities. 

However, even if such measurements were possible, would the uncertainty of the result be small enough to establish that production does indeed balance observed loss of ozone The calculation of ozone loss in the Antarctic ozone hole was shown to have an uncertainty of 35 to 50%. The uncertainty for analyzing whether production balances loss in the midlatitude stratosphere is similarly 35 to 50%. About half of the uncertainty is in the measurements of stratospheric abundances, which are typically 5 to 35%, and half is in the kinetic rate constants, which are typically 10 to 20% for the rate constants near room temperature but are even larger for rate constants with temperature dependencies that must be extrapolated for stratospheric conditions below the range of laboratory measurements. In addition to uncertainties in the photochemical rate constants, there are those associated with possible missing chemistry, such as excited-state chemistry, and the effects of transport processes that operate on the same time scales as the photochemistry. Thus, simultaneous measurements, even with relatively large uncertainties, can be useful tests of our basic understanding but perhaps not of the details of photochemical processes. 

These examples illustrate that an increasing number of trace gases must be measured simultaneously if even limited subsets of stratospheric photochemistry and transport are to be understood. The combined uncertainties will also become less of a constraint as simultaneous measurements of trace gas abundances can be compared to values derived from other observed abundances and simple photochemical relationships. As important is the improved measurement of photochemical parameters from laboratory studies as well as the search and study of other mechanisms that may be occurring in the stratosphere. Concerted effort in all of these categories is required to avert future failure in predicting shifts in stratospheric photochemistry, like the Antarctic ozone hole. 

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. 

Chance K, Traub W A, Johnson D G, Jucks K W, Ciarpallini P, Stachnik R A, Salawitch R J and Michelsen H A 1996 Simultaneous measurements of stratospheric HO and Cl-.c comparison with a photochemical model J. 

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 measurements in the midlatitude stratosphere during the last four years have been equally successful because more related species are being measured simultaneously, and these data sets are placing serious constraints on photochemical models (2). This situation is dramatically different from that in the mid-1970s through the mid-1980s, when confirmation that certain trace gas species were present in the stratosphere in approximately the correct abundances was still an issue (6). Analyses of more recent measure-... 

The recent solar mesosphere explorer (SME) satellite (Oct. 1981) measures simultaneously [O3], T, and solar uv intensity in the upper stratosphere [5, 6, 7]. This is a good altitude to test photochemical theories since photochemical lifetimes of species here are appreciably shorter than the time-scale for horizontal North to South redistribution. In the mesosphere, the results show quite clearly that the temperature (rather than solar flux) determines the Os concentration, although the results of other physical phenomena such as the solar flare of July 13, 1982 were clearly observeable. 

Pundt L, Van Roozendael M., Wagner T., Richter A., Chipperfield M., Burrows J. P., Fayt C., Hendrick F., Pfeilsticker K., Platt U., and Pommereau J.-P. (2000) Simultaneous UV-vis Measurements of BrO form Balloon, SateUite and Ground implications for tropospheric BrO. In Proc. 5th European Symp. on Polar Stratospheric Ozone 1999, Air Poll. Res. Report 73, EUR 19340 (eds. N. R. P. Harris, M. Guirlet, and G. T. Amanatidis). European Commission, Brussels, Belgium, pp. 316-319. 

More recent measurements have been reported by Lammerzahl et al. (2002). This work reports simultaneous CO2 and O3 isotope ratios from eight balloon flights from Kimna, Sweden and Aire-sur-TAdour, France. There is a correlation observed between and 5 0 of stratospheric CO2. The observed ratio is 1.71 0.03,... 

Girard, A., G. Fergant, L. Gramont, O. Lado-Bordowsky, J. Laurent, S. Le Boiteux, M. P. Lemaitre, and N. Louisnard (1983). Latitudinal distribution of ten stratospheric species deduced from simultaneous spectroscopic measurements. J. Geophys. Res. 88, 5377-5392. 

Simultaneous in situ measurements of CO2 and water vapor in the lower stratosphere in November 1992 and May 1993, for example, were analyzed to infer a mean transport time of 4 to 6 months from the tropical tropopause (—16 km) to — 18.5 to 19 km at midlatitudes (Boering et al., 1995). It takes many years for a species to reach the upper levels of the stratosphere from the time it crosses the tropopause. 

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