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The stratosphere can be used as an archive of past tropospheric conditions. Measurements of the long‐lived trace gases CF4, C2F6, and SF6 have been carried out on stratospheric air samples obtained by balloon borne cryosampling from altitudes of up to 34 km between 1987 and 1995. SF6 observations were used to ‘date’ the air samples. Above 25 km height the SF6 concentrations are lagging the tropospheric ones by several years: 4.5 years for the tropics, 6 years for mid‐latitudes and up to 10 years for the arctic winter vortex. The high ages of stratospheric air found inside the upper polar vortex may indicate that the lag of the peak halogen burden between the troposphere and the polar stratosphere is longer than previously assumed. The age information from SF6 allows to reconstruct tropospheric trends for CF4 and C2F6 since 1982. Accordingly, for the period 1982 to 1995, concentrations increased from 62 to 75 ppt for CF4 and from 1.5 to 2.6 ppt for C2F6. Mean increase rates of 1.00 ppt yr−1 for CF4 and 0.084 ppt yr−1 for C2F6 translate into annual injection rates of about 14,600 t yr−1 and 1,900 t yr−1 respectively. With aluminium production as the only major source, average emissions per ton of primary aluminium are thus calculated to be 0.77 kg for CF4 and 0.10 kg of C2F6 in 1994.

Various indications for shifts in plant and animal phenology resulting from climate change have been observed in Europe. This analysis of phenological seasons in Germany of more than four decades (1951±96) has several major advantages: (i) a wide and dense geographical coverage of data from the phenological network of the German Weather Service, (ii) the 16 phenophases analysed cover the whole annual cycle and, moreover, give a direct estimate of the length of the growing season for four deciduous tree species. After intensive data quality checks, two different methods ± linear trend analyses and comparison of averages of subintervals ± were applied in order to determine shifts in phenological seasons in the last 46 years. Results from both methods were similar and reveal a strong seasonal variation. There are clear advances in the key indicators of earliest and early spring (±0.18 to ±0.23 d y ±1 ) and notable advances in the succeeding spring phenophases such as leaf unfolding of deciduous trees (±0.16 to ±0.08 d y ±1 ). However, phenological changes are less strong during autumn (delayed by + 0.03 to + 0.10 d y ±1 on average). In general, the growing season has been lengthened by up to ±0.2 d y ±1 (mean linear trends) and the mean 1974±96 growing season was up to 5 days longer than in the 1951±73 period. The spatial variability of trends was analysed by statistical means and shown in maps, but these did not reveal any substantial regional differences. Although there is a high spatial variability, trends of phenological phases at single locations are mirrored by subsequent phases, but they are not necessarily identical. Results for changes in the biosphere with such a high resolution with respect to time and space can rarely be obtained by other methods such as analyses of satellite data.

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THESE volumes review recent research and development work in the physics chemistry, and technology of the in~ organic azides. Summarising fundamental advances over the past two decades, emphasis is placed on investigations supported by the United States Army through its Office of the Chi•ef of Research and Development and its Materiel Command. The contributing authors are, for the most part, members of the Energetic Materials Division (formerly Picatinny Arsenal), Armament Research and Development Command, New Jersey. The wide variation in crystal bonding characteristics and stability of the inorganic azides present problems of unique interest in solid state physics and chemistry. Tn the reactive state