Abstract. Tentative estimates, using three-dimensional chemistry and transport models, have suggested small ozone increases in the upper troposphere resulting from current aircraft emissions, but have also concluded to significant deficiencies in today's models and to the need to improve them through comparison with extended data sets. The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program was initiated in 1993 by European scientists, aircraft manufacturers, and airlines to collect experimental data. Its goal is to help understand the atmosphere and how it is changing under the influence of human activity, with particular interest in the effects of aircraft. MOZAIC consists of automatic and regular measurements of ozone and water vapor by five long range passenger airliners flying all over the world. The aim is not to detect direct effects of aircraft emissions on the ozone budget inside the air traffic corridors but to build a large database of measurements to allow studies of chemical and physical processes in the atmosphere, and hence to validate global chemistry transport models. MOZAIC data provide, in particular, detailed ozone and water vapor climatologies at 9-12 km where subsonic aircraft emit most of their exhaust and which is a very critical domain (e.g., radiatively and stratosphere/troposphere exchanges) still imperfectly described in existing models. This will be valuable to improve knowledge about the processes occuring in the upper troposphere and the lowermost stratosphere, and the model treatment of near tropopause chemistry and transport. During MOZAIC I (January 1993-September 1996), fully automatic devices were developed,

No abstract

The rate at which ozone is increasing in the troposphere is uncertain due to the lack of accurate long‐term measurements. Old ozone measurements obtained at the Pic du Midi Observatory (3000 m high, southwestern France) were recently rediscovered. Four sets of data available at this station are presented herein: (1) 1874–1881 and (2) 1881–1909 by the Schönbein method and (3) 1982–1984 and (4) 1990–1993 by UV absorption analyzers. The results show an increase in ozone by a factor of 5 since the beginning of the twentieth century, corresponding to an exponential increase of 1.6% per year, although this trend is probably higher (2.4% per year) for the last few decades. A stable 10 ppb ozone mixing ratio is observed during the first 20 years of the series, which is representative of the preindustrial era ozone level. The increase is seen to start around 1895. Other data, obtained at various European high‐altitude stations between 1920 and 1980, tie in closely with the Pic du Midi observations. A tentative evaluation of the impact of tropospheric ozone on radiative forcing confirms that ozone is currently the second most significant greenhouse gas, responsible for 22% and 13% of radiative forcing changes since 1800 in the northern and southern hemispheres, respectively. If these rates were to be maintained in the future, ozone would continue to evolve differently in the two hemispheres (maximum level in the northern hemisphere) and could make an even more significant contribution to the radiative forcing of the northern hemisphere.

-1995), shows good agreement in the free troposphere (800-300 hPa), no detectable bias for Hohenpeissenberg/Frankfurt, when taking into consideration the various causes of discrepancies (Dobson normalization, ozone geographical variations). Indeed, the results of this analysis support the hypothesis that it is not advantageous to scale the ozone sonde data to the overhead ozone column; the scaling appears to cause overestimation of the tropospheric 03 concentrations, by about 3-6% at Hohenpeissenberg, and to cause more scatter in the sonde-MOZAIC differences. The correspondence between the OSN and MOZAIC climatologies obtained in very different conditions demonstrates that they are representative of the atmosphere and that, being complementary while each retains its own advantages, they are therefore both useful for validation studies.

letters to nature 316 NATURE | VOL 398 | 25 MARCH 1999 | www.nature.com in the imprinted sites, whereas predominantly aragonite was formed in solution, as expected. In some cases an occasional needle-like crystal of aragonite could be seen, which had probably been deposited onto the polymer particle during ®ltration and drying (compare Fig. 4e and g). More signi®cantly, examination of the surface of control polymer CP-2 ( Fig. 4h) revealed the presence of deposited aragonite needles as well as a few sharp-edged`solution-type' calcite crystals. A crystal-enriched fraction from PI-1, prepared by grinding and sedimentation in chloroform, was shown conclusively to contain calcite, both by FT-IR (Fig. 3b) and XRD (not shown).We attempted to produce aragonite-speci®c polymers using the same monomer 1 and the needles shown in Fig. 4g as template. But the results of this experiment were inconclusive, as the polymers did not nucleate as well as those imprinted with calcite and neither FT-IR nor powder XRD were sensitive enough to quantify the ratio of aragonite to calcite on the polymer surface. It is not clear why the imprinting of calcite should result in much more ef®cient nucleation than the corresponding aragonite imprints. However, as the arrangement of ions on the crystal planes of each polymorph are different, it is reasonable to expect that a functionality which is suitable for creating complementary surfaces in one case may not necessarily be useful for another type of crystal. We note that the use of acrylic and methacrylic acids in place of the monomer 1 resulted in imprinted polymers with inferior nucleating abilities. The reason for this is not clear, but may be due to the presence of the¯exible spacer which separates the acid head group from the polymerizable double bond of 1, allowing this monomer to match more easily the spacing of ions on the crystal surface and for this ordering to be preserved throughout the entire imprinting process. Better understanding of these processes may enable the design of devices for generating crystals of the desired type, size or shape for applications in materials science. In addition, the ability to generate surfaces speci®c to crystals of an enantiomerically pure organic compoundÐto promote its crystallization from a racemic mixtureÐ may lead to the introduction of new separation methods in the pharmaceutical and ®ne-chemical industries. M