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Matrix isolation Fourier transform IR spectroscopy has been used for studying the products and mechanism of the silicon tetrafluoride reaction with water at various component ratios and reaction durations. Assignment of new bands in the spectrum confirms the earlier assumptions of first the formation of a molecular complex with water and later of trifluorosilanol, which finally condenses to give hexafluorodisiloxane.

A new autonomous balloon-borne sounding system for the measurement of stratospheric trace gas profiles was designed and constructed. Major components of the sonde are a miniature grating spectrometer, which covers a wavelength range from the ultraviolet (200 nm) to the visible (850 nm), and a commercial radiosonde. The low-weight sonde (approximately 1.7 kg) measures the spectral solar irradiance and meteorological parameters during the ascent through the atmosphere. Because of the decreasing ambient temperature during an ascent, the temperature of the spectrometer decreases by about 15 K. Active temperature stabilization is not included, and the irradiance measurements show a strong temperature dependence. The temperature-induced wavelength shift, the absolute irradiance, and the dark signal behavior were characterized as a function of the spectrometer’s temperature. Based on this laboratory characterization, an inflight correction for changes in the dark current and for the wavelength drift was applied. In the test program described herein, ozone profiles were determined from changes in the measured solar spectral irradiance caused by ozone absorption in the Hartley and Huggins bands. Comparisons were performed with results of simultaneous electrochemical ozonesonde and lidar measurements. The ozone number density profile retrieved using the new sonde agrees with the independently measured ozone profiles within 20% for altitudes above 18 km. In the lower stratosphere, the discrepancies increase to 50%.

The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF4 samples differing in purity, we have identified rovibrational bands arising from Si2F6O, SiF3OH, HF, SiF3H, SiF2H2, SiH3F, CH4, CO2, and CO impurities. Their detection limits lie in the range 9 x 10(-5) (CO2) to 3 x 10(-3) mol % (Si2F6O). In the spectra of SiH4 samples of different purity, we have detected CH4, CO2, SiF3H, SiF2H2, and SiF4 impurities. Their detection limits lie in the range 8 x 10(-5) (CO2) to 1 x 10(-3) mol % (SiF4).

Experimental observations and data from quantum chemical calculations on complexes between water molecules and small, oxygen-containing inorganic species that play an important role as oxidants in the atmosphere (O(1D), O(3P), O2(X3sigmag), O2(b1sigmag+), O3, HO, HOO, HOOO, and H2O2) are reviewed, with emphasis on their structure, hydrogen bonding, interaction energies, thermodynamic parameters, and infrared spectra. In recent years, weakly bound complexes containing water have increasingly attracted scientific attention. Water in all its phases is a major player in the absorption of solar and terrestrial radiation. Thus, complexes between water and other atmospheric species may have a perceivable influence on the radiative balance and contribute to the greenhouse effect, even though their concentrations are low. In addition, they can play an important role in the chemistry of the Earth's atmosphere, particularly in the oxidation of trace gases. Apart from gas-phase complexes, the interactions of oxidants with ice surfaces have also received considerable advertency lately due to their importance in the chemistry of snow, ice clouds, and ice surfaces (e.g., ice shields in polar regions). In paleoclimate--respectively paleoenvironmental--studies, it is essential to understand the transfer processes from the atmosphere to the ice surface. Consequently, special attention is being paid here to the intercomparison of the properties of binary complexes and the complexes and clusters of more complicated compositions, including oxidants adsorbed on ice surfaces, where ice is considered a kind of large water cluster. Various facts concerning the chemistry of the Earth's atmosphere (concentration profiles and possible influence on radical reactions in the atmosphere) are discussed.

The spectral characteristics of the SiF4 molecule in the range 3100700 cm1, including the absorption range of the band 3, are studied in the gas phase at P = 0.47 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 23, 3 + 1, 3 + 4, and 34 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF4, the integrated absorption coefficient of the absorption band 3 of the 28SiF4 molecule was measured to be A(3) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(3) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ. ©2005 Pleiades Publishing, Inc.

Phosphine (PH3), was recently found worldwide even in the remote atmosphere (Naturwissenschaften83(1996a)131; Atmos. Environ. 37(2003)24 29). It is of interest to find natural mechanisms which could produce phosphine gas and drive a volatile link of the atmospheric phosphorus cycle and the formation of phosphoric acid as possible condensation nuclei for clouds. Here, we report on simulated lightning exposing sodium phosphate in a reducing medium (methane model atmosphere or organic matter) for 5 s to a spark induced by microwave. The gas product analyzed by gas chromatography contained phosphine (yield up to 0.6 g kg 1 phosphate P) and methylphosphine (CH3)PH2 (yield up to 0.02 gkg 1 phosphate P). We suggest a plasma-chemical formation mechanism where organic compounds or methane or secondary hydrogen thereof reduce phosphate to phosphine of which a small fraction can subsequently react with methyl radicals to form methylphosphine. A small yield of 6 mgphosphine per kgphosphate P was even obtained in methane free medium, by simple plasmatic recombination of inorganic phosphorus. We believe that methane and hydrogen are useful model substances of pyrolytic gases with high reducing power which may form if lightning strikes biomass, soil and aerosol. These results suggest evidence that phosphine and methylphosphine (detectable in the field by intense garlic odor) are produced when atmospheric lightning strikes the ground or aerosol which is containing oxidized forms of phosphorus and chemical reductants. Additional reviewed data show that laboratory lightning was able to reduce a much more significant portion of phosphate to phosphite (up to 25% yield), methylphosphonic acid (up to 8.5% yield) and traces of hypophosphite in a matter of seconds. r 2004 Elsevier Ltd. All rights reserved.

Tower-based measurements of hydrogen peroxide (H2O2) and formaldehyde (HCHO) exchange were performed above the snowpack of the Greenland ice sheet. H2O2 and HCHO fluxes were measured continuously between 16 June and 7 July 2000, at the Summit Environmental Observatory. The fluxes were determined using coil scrubber-aqueous phase fluorometry systems together with micrometeorological techniques. Both compounds exhibit strong diel cycles in the observed concentrations as well as in the fluxes with emission from the snow during the day and the evening and deposition during the night. The averaged diel variations of the observed fluxes were in the range of +1.3 � 10 13 molecules m � 2 s � 1 (deposition) and � 1.6 � 10 13 molecules m � 2 s � 1 (emission) for H2O2 and +1.1 � 10 12 and � 4.2 � 10 12 molecules m � 2 s � 1 for HCHO, while the net exchange per day for both compounds were much smaller. During the study period of 22 days on average ð0:8 þ4:6 � 4:3 Þ� 10 17 molecules m � 2 of H 2O2 were deposited and ð7:0 þ12:6 � 12:2 Þ� 10 16 molecules m � 2 of HCHO were emitted from the snow per day. A comparison with the inventory in the gas phase demonstrates that the exchange influences the diel variations in the boundary layer above snow covered areas. Flux measurements during and after the precipitation of new snow shows that o16% of the H2O2 and more than 25% of the HCHO originally present in the new snow were available for fast release to the atmospheric boundary layer within hours after precipitation. This release can effectively disturb the normally observed diel variations of the exchange between the surface snow and the atmosphere, thus perturbing also the diel variations of corresponding gas-phase concentrations. r 2002 Elsevier Science Ltd. All rights reserved.

Results from a measurement campaign performed at Table Mountain Facility/Jet Propulsion Laboratory/ California Institute of Technology (34.388N, 117.688W, 2280 m ASL) are presented. Between 19 February and 18 March 1997 more than 400 h worth of lidar data were acquired and four backscatter sondes were launched. About 50% of the observations show the presence of cirrus clouds at altitudes close to and below the tropopause. Of these clouds 80% are characterized as subvisual with optical depths below 0.03 at a wavelength of 532 nm. Simple geometrical considerations lead to cloud spatial scales of 0.31 km vertically and 7.5 km horizontally, respectively. Deviations from color ratio values derived on the basis of geometrical optics are interpreted as small particle signatures. Comparing backscatter ratio profiles observed concurrently by three aerosol lidars, mean deviations of about 10% are found.

The latitudinal variations of atmospheric trace gas column abundances have been measured during a ship cruise between 57°N and 45°S on the central Atlantic. The measurements were performed in October 1996 using high-resolution solar absorption spectroscopy in the infrared. The analysis method employed permits the retrieval of the total column densities of 20 different trace gases and for a few compounds the vertical mixing ratio profiles. For CH4 an interhemispheric difference of 3% was observed. The total columns of the shorter-lived trace gases CO and C2H6, analyzed between 57°N and 45°S, reveal a slight maximum in the tropics and a substantial increase north of 45°N. The total columns of C2H2 and HCN, detectable between 30°N and 30°S, reveal a maximum in the tropics of the Southern Hemisphere. For CH2O, studied between 57°N and 45°S, a well-pronounced maximum is observed in the tropics. The profile retrieval gives high mixing ratios for CO, C2H6, and O3 north of 40°N in the lower troposphere. In the tropics high concentrations are found for all three compounds in the entire troposphere, even above 12 km. The measurements have been used to estimate averaged mixing ratios of the trace gases for the free troposphere between 0 and 12 km. In the tropics the data give high values: for example, more than 200 pptv for HCN, 750 pptv for CH2O, 100 ppbv for CO and 100 pptv for C2H2. These values are comparable to or higher than what has been observed at midlatitudes, indicating the importance of biomass burning emissions on the tropospheric composition.

Understanding the NOy budget at high latitudes is important for our knowledge of present-day clean air chemistry and essential for reliable interpretation of existing ice core nitrate data. However, measurements of NOy components at high latitudes have been limited, and no measurements have attempted to address the budget of NOy. Here we report on a campaign conducted in the austral summer of 1997 at the German Antarctic research station, Neumayer, with first Antarctic measurements for NOy in addition to light alkyl nitrates, NO, HNO3 and p−NO3−. Inorganic nitrate has generally been assumed to be the dominant component of NOy in Antarctica, although this idea has not previously been tested. However, our results show that for this coastal station, methyl nitrate was present in much higher concentration than inorganic nitrate (median CH3ONO2 = 38 pptv, HNO3 = 5 pptv). It has been suggested earlier that some alkyl nitrates might have a marine source. If this suggestion is correct, the implication arises that the oceans are an important source of NOy to the Antarctic troposphere and that their role in determining nitrate concentrations in ice must be considered.

The reaction of chlorine nitrate with hydrogen chloride catalysed by sulfuric acid molecules and by the hydrogen sulfate anion has been investigated by means of abinitio calculations at Hartree–Fock and MP2 levels of theory. Geometries of reactants, products and transition states have been optimized using 6-31G** and 6-31++G(2D,2P) basis sets. While the reaction barrier of the gas phase reaction does not decrease significantly with sulfuric acid, it vanishes completely if the hydrogen sulfate anion is involved. The reaction occurs in several associative steps which do not have a reaction barrier. Implications of the results for heterogeneous reactions in the stratosphere on sulfuric acid aerosol surfaces or in the bulk are discussed.

The atmospheric concentration of peroxyacetyl nitrate (PAN) was measured over the South Atlantic Ocean in the range between 37° and 70°S in March 1999 in order to investigate its latitudinal distribution and its role in the NOy chemistry of the remote marine boundary layer (MBL) in the high latitudes of the southern hemisphere. The measurements were performed using an automatic gas chromatographic system aboard RV Polarstern. Mean mixing ratios of 62(±21) pptv were obtained between 37° and 49°S. South of 55°S, PAN concentrations were very low with values of the order of 10–30 pptv. Pronounced diurnal cycles could not be observed. The concentrations over the South Atlantic were considerably lower compared with the North Atlantic where the MBL is influenced by continental air masses.

Ground based millimeter-wave measurements of Arctic stratospheric ozone in the winter 1996/97 are presented. The measurements have been performed at one of the primary Arctic stations of the Network for the Detection of Stratospheric Change (NDSC) in Ny-Alesund, Spitsbergen (78.9°N, 11.9°E). Over the period 11 February to 26 April the measurements show an ozone mixing ratio decrease of 1.3 ppm in the lower stratosphere. Correspondingly, stratospheric ozone column densities decreased by more than 50 DU. Taking into account the transport of ozone due to diabatic decent, we estimated chemical ozone loss rates of 22 ppb/day in February decreasing to 15 ppb/day in late April 1997.

We have performed measurements of stratospheric chlorine monoxide (ClO) in Ny-Alesund, Spitsbergen (78.9° N,11.9°E), using a ground-based mm-wave radiometer. In this paper we describe the observed degree of chlorine activation inside the polar vortex in the winter 1996/97. We obtained daily averaged ClO mixing ratios for the lower stratospheric layer on 20 days covering the period from mid-February until the beginning of April. The volume mixing ratio of the lower ClO peak at an altitude of approximately 21 km reached a maximum of 1.6 ppbv. These measurements support the strong chemically induced ozone depletion which was found until April 5 by simultaneous ozone measurements reported in a companion paper [Sinnhuber et al., 1998]. They observed an unusual ozone loss in late April, which corresponds to the observed ClO abundance on April 18-22. On several days we observed diurnal ClO cycles which were compared with model calculations.

The dynamics of tropospheric ozone variations in the Arctic (Ny-A lesund, Spitsbergen, 79°N, 12°E) and in Antarctica (Neumayer-Station, 70°S, 8°W) were investigated for the period January 1993 to June 1994. Continuous surface ozone measurements, vertical profiles of tropospheric ozone by ECC-sondes, meteorological parameters, trajectories as well as ice charts were available for analysis. Information about the origins of the advected air masses were derived from 5-days back-trajectory analyses. Seven tropospheric ozone minima were observed at Ny-A lesund in the period from March to June 1994, during which the surface ozone mixing ratios decreased from typical background concentrations around 40 ppbv to values between 1 ppbv and 17 ppbv (1 ppbv O 3 corresponds to one part of O 3 in 10 9 parts of ambient air by volume). Four surface ozone minima were detected in August and September 1993 at Neumayer-Station with absolute ozone mixing ratios between 8 ppbv and 14 ppbv throughout the minima. At both measuring stations, the ozone minima were detected during polar spring. They covered periods between 1 and 4 days (Arctic) and 1 and 2 days (Antarctica), respectively. Furthermore, it was found that in both polar regions, the ozone depletion events were confined to the planetary boundary layer with a capping temperature inversion at the upper limit of the ozone poor air mass. Inside this ozone- poor layer, a stable stratification was obvious. Back-trajectory analyses revealed that the ozone-depleted air masses were transported across the marine, ice-covered regions of the central Arctic and the South Atlantic Ocean. These comparable observations in both polar regions suggest a similar ozone destruction mechanism which is responsible for an efficient ozone decay. Nevertheless, distinct differences could be found regarding the vertical structure of the ozone depleted layers. In the Arctic, the ozone-poor layer developed from the surface up to a temperature inversion, whereas in the Antarctic, elevated ozone-depleted air masses due to the influence of catabatic surface winds, were observed. DOI: 10.1034/j.1600-0889.1998.00003.x

The air chemistry investigations, performed on R/V Polarstern during the expedition ARK X/1 in July/August 1994, comprised a mapping of the vertical ozone distribution by ozone soundings and the surface mixing ratios of H2O2 and NO above the East Greenland Sea between 70°N and 80°N. The observed H2O2 mixing ratios varied from about 100 parts per trillion by volume (pptv) up to around 1000 pptv. Surface ozone concentrations can be correlated with the source region of the advected air masses. Ozone mixing ratios from around 33 parts per billion by volume (ppbv) up to 60 ppbv have been observed in air parcels emanating from industrialized regions. In contrast, pristine Arctic air masses showed low ozone mixing ratios of about 23 ppbv. The tropospheric part of the vertical ozone profiles occasionally exhibited significant maxima above the planetary boundary layer. Apart from cases where intrusions of stratospheric ozone were obvious, photochemical ozone formation along trajectories originating from polluted regions was most probably the reason for layers with enhanced ozone concentrations. The measured surface NO mixing ratios were extremely low, typically between 3 and 8 pptv. Thus local photochemical surface ozone production could be largely ruled out. In conclusion it can be stated that in summer, intrusion of ozone rich stratospheric air and advection of polluted air masses from lower latitudes appeared to be the dominant ozone sources of the marine Arctic troposphere.

The vertical ozone distribution over the Atlantic Ocean has been measured in situ by shipborne ozone soundings during three RV Polarstern meridional transects in January/February 1993, October/November 1993, and May/June 1994. The low ozone column densities measured by Nimbus 7 and Meteor 3 satellites in 1993 could be confirmed by our investigations. We observed distinct differences in the vertical distribution pattern of tropospheric ozone between the northern and the southern hemisphere: The ozone mixing ratio gradients were flat in the northern hemisphere and ozone mixing ratios in the free troposphere never did exceed 80 parts per billion by volume (ppbv) up to the tropopause, while the southern hemisphere exhibited a pronounced vertical gradient. Extremely dry air masses with enhanced ozone amounts up to 120 ppbv have been found in the tropical free troposphere of the southern hemisphere between 0° and 20°S. The vertical ozone stratification in the troposphere of the southern hemisphere was dominated by this large-scale feature. Photochemical ozone production as a consequence of the emissions of natural fires or intrusions of stratospheric air masses are the most probable sources for these ozone-rich layers. On the basis of our results, a stringent differentiation between both alternatives could not be given.

During the EASOE campaign ground-based FTIR measurements have been performed in March 1992 at Ny-Alesund (Spitsbergen, 79°N, 12°E) to derive column amounts of several trace gases. For the first part of the measurement campaign Ny-Alesund was situated inside the polar vortex. The obtained concentrations of N2O, CH4 and HF inside the vortex are consistent with subsidence. The ratio of HClstrat/HF varied from about 2.0 inside to about 2.8 outside the vortex. Inside the vortex low values for NO2 and high values for HNO3 were found. The O3 concentrations inside the vortex are slightly lower than what was observed outside the vortex.

Within the period of December 1992 to March 1993 lidar investigations of stratospheric aerosols were performed at Ny-Alesund, Spitsbergen (79°N, 12°E). Backscatter signals at wavelengths of 353, 532 and 1064 nm and depolarization signals at 532 nm in altitudes ranging from the tropopause up to 30 km were analyzed. Throughout the whole measurement period we observed an aerosol layer of volcanic origin in the lower stratosphere. Depolarization profiles suggest that the volcanic aerosol layer consisted mainly of liquid droplets. Comparison with model calculations indicate median particle radii between 0.1 and 0.2 µm. Surface densities exceeded approximately 40 µm²/cm³ in the lower part of the layer around 12 km. In January 1993 polar stratospheric clouds (PSCs) were frequently observed at altitudes up to 22 km. We analyzed the backscatter and depolarization data with respect to the temperature history of backward trajectories reaching Ny-Alesund. Signatures for micron sized crystalline PSC particles appear for cooling rates of −1 to −3 K day−1. Larger cooling rates of −4 to −10 K day −1 produced submicron sized aerosols, presumably supercooled droplets, characterized by enhanced backscatter ratios and reduced depolarization.

In winter 1992/93 we have performed ground-based FTIR measurements in the Arctic (79°N, 12°E) to derive column densities of stratospheric trace gases within the polar vortex. Due to the polar night the moon had to serve as infrared light source instead of the sun. It was possible to perform FTIR-measurements for about a week around full moon. Column densities of N2O, CH4, HF, HCl, O3, NO2, HNO3 and ClONO2 have been obtained. The spectra were recorded at 0.01 cm−1 or 0.02 cm−1 resolution using MCT or InSb detectors. Measurements with an aerosol lidar performed at the same site show that polar stratospheric clouds (PSCs) appeared several times during the polar night. It seems that the concentrations of the stratospheric trace gases are strongly influenced by the occurrence of PSCs.

Concentrations of H2O2 in gas phase and seawater have been measured in pristine regions of the Atlantic Ocean during the RV Polarstern expedition ANT X-1 from 11/15/91 to 01/02/92. A broad maximum of gaseous H2O2 mixing ratio in the troposphere was found between the tropic of cancer and the tropic of capricornus with peak values around 1.8 ppbv. The observed ratio of organic peroxides/total amount of peroxides was 0.2-0.35, in contrast to the remarkably lower ratio of 0.05-0.10 measured in the continental troposphere by other groups. In the Atlantic surface seawater the H2O2 concentrations were determined to be around 0.1 mmol/L, decreasing with increasing water depth to a value below the detection limit at approximately 100 m. We observed low H2O2 concentrations (= 0.03 mmol/L) in surface water in coastal shelf regions and in the partly ice covered Weddell Sea.

A LIDAR instrument for measurements of the ozone concentration and of aerosols in the middle atmosphere is briefly described. Data sets for ozone and aerosols, obtained at Spitsbergen during winter and early spring in 1989 and 1990, are presented. The Arctic ozone layer was found to be strongly influenced by atmospheric dynamics; a dramatic ozone depletion was not observed. Polar stratospheric clouds were detected in each winter, their dependence on the ambient atmospheric temperature is described.

The present report provides information about lead concentrations in Atlantic surface waters over a wide geographical range. Differential pulse anodic stripping voltammetry (DPASV) was applied for the analysis of lead in surface water of the Atlantic Ocean. Sampling on board of the research vessel Polarstern was performed from the bow boom of the ship but also with a newly installed snorkel system which allowed continuous sampletaking. In both cases special precautions were taken in order to avoid contamination by the ship. A limited number of samples could immediately be measured aboard Polarstern in a newly constructed clean room laboratory container. A part of the samples had to be irradiated before the voltammetric measurement. In 1989 lead concentrations in the North Atlantic between 22° N and 46° N continuously increased from 42.5 pmol/kg up to 147 pmol/kg. The comparison with results from a cruise in 1981 shows that the lead concentration in the eastern North Atlantic has diminished by more than 50%. A similar trend is documented for the consumption of alkyl leaded gasoline in the United States of America. Seawater samples from a cruise in 1990 exhibited a very low background concentration of 6.1–14 pmol/kg Pb in the middle Atlantic, while higher values were measured in the Intertropical Convergence Zone (ITCZ). In a certain area of the Atlantic Ocean lead has been identified as a tracer for terrigenous input, in another area, however, as a transient tracer for anthropogenic input. This demonstrates that atmospheric input of lead into the surface water of the Atlantic can have different origins.

Atmospheric aerosols play an important role in global climate change, directly through radiative forcing and indirectlythrough their effect on cloud properties. Numerous measurements have been performed in the last three decades inorder to characterize polar aerosols. Information about aerosol characteristics is needed to calculate induced changes inthe Earth’s heat balance. However, this forcing is highly variable in space and time. Accurate quantification of forcingby aerosols will require combined efforts, assimilating information from different sources such as satellite, aircraft andsurface-based observations. Adding to the complexity of the problem is that the measurements themselves are oftennot directly comparable as they vary in spatial/temporal resolution and in the basic properties of the aerosol that theymeasure. Therefore it is desirable to close the gap between the differences in temporal and spatial resolution and coverageamong the observational approaches. In order to keep the entire information content and to treat aerosol variability ina consistent and manageable way an approach has to be achieved which enables one to combine these data. This studypresents one possibility for linking together a complex Arctic aerosol data set in terms of parameters, timescale and placeof measurement as well as meteorological parameters. A cluster analysis was applied as a pattern recognition technique.The data set is classified in clusters and expressed in terms of mean statistical values, which represent the entire databaseand its variation. For this study, different time-series of microphysical, optical and chemical aerosol parameters aswell as meteorological parameters were analysed. The database was obtained during an extensive aerosol measurementcampaign, the ASTAR 2000 (Arctic Study of Tropospheric Aerosol and Radiation) field campaign, with coordinatedsimultaneous ground-based and airborne measurements in the vicinity of Spitsbergen (Svalbard). Furthermore, longtermmeasurements at two ground-based sites situated at different altitudes were incorporated into the analysis. Theapproach presented in this study allows the necessary linking of routine long-term measurements with short-termextensive observations. It also involves integration of intermittent vertical aerosol profile measurements. This is usefulfor many applications, especially in climate research where the required data coverage is large. DOI: 10.1111/j.1600-0889.2004.00128.x

[1] High-altitude tropical cirrus (TC) have been observed by lidar during a cruise of the German research vessel ‘Polarstern’ above the Atlantic between 8°S and 12°. The backscatter lidar data give a detailed picture of the vertical structure of the clouds with a high time resolution. Using the data of radiosondes, which were launched twice a day aboard ‘Polarstern,’ the temperature of the clouds as well as the structure of the tropical tropopause is characterized. The clouds are found in an altitude between 14 km and 17 km, with a mean optical depth of τ = 0.02 and a mean temperature of 198 K. Tropical Cirrus appear in two distinct layers which are separated by a change in wind direction. This structure was observed south as well as north of the ITCZ. Cloud tops are often found at the thermal tropopause, in some case these clouds are of the ultra-thin type.

[1] Cirrus clouds have been probed at two locations in the midlatitudes of the southern (SH) and northern hemisphere (NH) with a Mobile Raman Aerosol Lidar (MARL) as part of the European INCA field experiments in 2000. MARL offers the opportunity to observe visible and subvisible clouds and to determine the optical depth τ in a range from below 10−3 up to 3. Despite different synoptic conditions we find at both locations similar macrophysical cloud properties, like mean base and top temperature among others. The frequencies of the optical depth show a characteristic distribution with a high share of subvisible clouds at both locations. While thin haze layers are frequently detected in the NH alone, we find highly depolarizing cirrus clouds only in the SH. These differences indicate that different cirrus properties and formation mechanisms are present at the two sites.

For the first time, an infrared investigation of gas phase hydrogen bonded complexes formed by hdyrogen fluoride with alcohols has been made. Evidence has been given for the formation of 1 : 1 heterodimers ROH ⋯ HF and the vibration wavenumbers [graphic omitted](F–H) have been estimated. The wavenumber displacements of the HF stretching vibration on H bond formation provide a measure of the electron donating abilities in the free alcohols. The electron donating power of the oxygen atom is increased by increasing methylation at the oxygen atom, as indicated by the constant increase of 75 cm–1 min Δ[graphic omitted]HF along the series H2O ⋯ HF, CH3OH ⋯ HF, (CH3)2O ⋯ HF. A similar but attenuated increase occurs on increasing methylation of the carbon atom in methanol as indicated by steps of about 25 cm–1 in Δ[graphic omitted]HF for complexes formed by CH3OH, CH3CH2OH, (CH3)2CHOH and (CH3)3COH. On the other hand, the electron donating ability of the oxygen atom is decreased by the presence of the electron attracting groups CH2Cl, CH2F and CF3. We confirm that where the vapour pressure of a component is a limitation on observing dimer formation in the gas phase, as is the case in most alcohols, it is advantageous to work at higher temperatures.

Recent progress in Fourier transform IR and far IR investigation of intermolecular interactions in liquid solutions and cryogenic matrices will be reported. Particular emphasis is given to routine performance checks of the spectrometer and to novel techniques of sample preparation and related equipment. The described examples are the dynamics of H2O isolated in solid Ar and the aggregational behaviour of HCN and CH3CN in diverse liquid and solid phases.