Search

The structures, energies, harmonic vibrational frequencies, and thermodynamic parameters of the water clusters (H2O)48, (H2O)72, and (H2O)270 were calculated using the standard DFT theory (BLYP/6-31++G(d,p) for small and medium clusters) and the modern tight-binding method SCC-DFTB (DFTBA and DFTB+). The adsorption and embedding of s-cis- and s-trans-glyoxal molecules as well as its sunlight UV photolysis products (molecules CH2O, HCOOH, H2O2, CO, CO2 and radicals CHO, HO, HO2) on nanosized ice clusters of up to 2.5 nm in diameter were studied within the above theoretical models. The structures of adsorption complexes on different sites of ice nanoparticles, the corresponding adsorption energies and thermodynamic parameters were estimated. We found that the DFTB method is a very promising tool for the calculations of structures and energies of ice nanoparticles, when compared to both DFT and semiempirical (PM3) methods. The obtained results are discussed in relation to the possible photolysis pathways, the reaction rates in the gas phase and in the adsorbed state, and the mechanisms of glyoxal photolysis catalyzed by the ice nanoparticles in the Earth’s atmosphere.

The low-temperature interaction between methyl hydroperoxide CH3OOH (MHP) and the hexagonal water ice surface was studied using DFT (BLYP/6-31++G(d,p)) calculations. The structures, energies, and some thermodynamic properties of the molecular complexes between MHP and the water clusters (H2O)48, (H2O)56, (H2O)72 representing the surface fragments of the (0001), (1010), and (1120) crystallographic planes of the hexagonal oxygen lattice of the water ice Ih with proton ordering corresponding to Pisani’s P-ordered model were calculated. The various modes of coordination and intrusion were studied using the extended set (up to 192 points for each plane) of the structures optimized at the semiempirical (PM3) level. The validity of the surface models was verified by the stability of the results obtained in the cluster series (H2O)n, (n = 48, 72, 192, 216) at the semiempirical level as well as by DFT calculations of selected structures at the BLYP/6-311++G(2d,2p) level.

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.

Semiempirical (PM3) and DFT (B3LYP/6-31++G(d,p)) calculations of the structure and energies of the variety of water clusters modeling 4680 fragments of the ice surface with different topology of the hydrogen bond network have been performed in order to analyze the contributions of various orientational isomers into the energy distributions of clusters and their impact onto the adsorption ability relatively to the H 2 O 2 molecule. It was found that, in the framework of the considered model, only several kinds of surface patterns among all the possible structures have significant thermodynamic weights and, thus, have the maximum contributions into the adsorption energy. Structural and energetic properties of the adsorption complexes formed by H 2 O 2 molecule with the most favourable fragments of the ice surface are analyzed on the basis of B3LYP/6-311++G(2d,2p) calculations.

Hydrogen chloride (HCl) and hydrogen fluoride (HF) are respectively the main chlorine and fluorine reservoirs in the Earth's stratosphere. Their buildup resulted from the intensive use of man-made halogenated source gases, in particular CFC-11 (CCl3F) and CFC-12 (CCl2F2), during the second half of the 20th century. It is important to continue monitoring the evolution of these source gases and reservoirs, in support of the Montreal Protocol and also indirectly of the Kyoto Protocol. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is a space-based instrument that has been performing regular solar occultation measurements of over 30 atmospheric gases since early 2004. In this validation paper, the HCl, HF, CFC-11 and CFC-12 version 2.2 profile data products retrieved from ACE-FTS measurements are evaluated. Volume mixing ratio profiles have been compared to observations made from space by MLS and HALOE, and from stratospheric balloons by SPIRALE, FIRS-2 and Mark-IV. Partial columns derived from the ACE-FTS data were also compared to column measurements from ground-based Fourier transform instruments operated at 12 sites. ACE-FTS data recorded from March 2004 to August 2007 have been used for the comparisons. These data are representative of a variety of atmospheric and chemical situations, with sounded air masses extending from the winter vortex to summer sub-tropical conditions. Typically, the ACE-FTS products are available in the 10–50 km altitude range for HCl and HF, and in the 7–20 and 7–25 km ranges for CFC-11 and -12, respectively. For both reservoirs, comparison results indicate an agreement generally better than 5–10% above 20 km altitude, when accounting for the known offset affecting HALOE measurements of HCl and HF. Larger positive differences are however found for comparisons with single profiles from FIRS-2 and SPIRALE. For CFCs, the few coincident measurements available suggest that the differences probably remain within ±20%.

The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar occultation technique. One of these instruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volume mixing ratio (VMR) profiles of nitrous oxide (N 2 O) from the upper troposphere to the lower mesosphere at a vertical resolution of about 3–4 km. In this study, the quality of the ACE-FTS version 2.2 N 2 O data is assessed through comparisons with coincident measurements made by other satellite, balloon-borne, aircraft, and ground-based instruments. These consist of vertical profile comparisons with the SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR, and single balloon flights of SPIRALE and FIRS-2, and partial column comparisons with a network of ground-based Fourier Transform InfraRed spectrometers (FTIRs). Overall, the quality of the ACE-FTS version 2.2 N 2 O VMR profiles is good over the entire altitude range from 5 to 60 km. Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between -42 ppbv and +17 ppbv, with most within ±20 ppbv. This corresponds to relative deviations from the mean that are within ±15%, except for comparisons with MIPAS near 30 km, for which they are as large as 22.5%. Between 18 and 30 km, the mean absolute differences are generally within ±10 ppbv, again excluding the aircraft and balloon comparisons. From 30 to 60 km, the mean absolute differences are within ±4 ppbv, and are mostly between -2 and +1 ppbv. Given the small N 2 O VMR in this region, the relative deviations from the mean are therefore large at these altitudes, with most suggesting a negative bias in the ACE-FTS data between 30 and 50 km. In the comparisons with the FTIRs, the mean relative differences between the ACE-FTS and FTIR partial columns are within ±6.6% for eleven of the twelve contributing stations. This mean relative difference is negative at ten stations, suggesting a small negative bias in the ACE-FTS partial columns over the altitude regions compared. Excellent correlation ( R =0.964) is observed between the ACE-FTS and FTIR partial columns, with a slope of 1.01 and an intercept of -0.20 on the line fitted to the data.

Recent experiments on the UV and electron beam irradiation of solid O2 reveals a series of IR features near the valence antisymmetric vibration band of O3 which are frequently interpreted as the formation of unusual On allotropes in the forms of weak complexes or covalently bound molecules. In order to elucidate the question of the nature of the irradiation products, the structure, relative energies, and vibrational frequencies of various forms of On (n = 1-6) in the singlet, triplet, and, in some cases, quintet states were studied using the CCSD(T) method up to the CCSD(T,full)/cc-pCVTZ and CCSD(T,FC)/aug-cc-pVTZ levels. The results of calculations demonstrate the existence of stable highly symmetric structures O4 (D3h), O4 (D2d), and O6 (D3d) as well as the intermolecular complexes O2·O2, O2·O3, and O3·O3 in different conformations. The calculations show that the local minimum corresponding to the O3···O complex is quite shallow and cannot explain the ν3 band features close to 1040 cm(-1), as was proposed previously. For the ozone dimer, a new conformer was found which is more stable than the structure known to date. The effect of the ozone dimer on the registered IR spectra is discussed.

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.

The molecular reaction pathways of SO3 and SOCl2 reactions with one and two water molecules were studied using ab-initio and DFT quantum chemical methods (up to MP2/6-311++G(3df,3pd) and QCISD(T)/6-311++G(2df,2pd)) in order to describe the experimentally observed kinetic features of SO3 hydration and SOCl2 hydrolysis in the gas phase and to elucidate the reaction mechanism providing the high reaction rate. The transition state structures were located, and absolute values of kinetic rate constants were estimated for a variety of possible reaction pathways including bi- and termolecular SO and S−Cl bond hydrolysis, chlorine shift to oxygen, dissociative addition with formation of hexavalent sulfur derivative, and adjacent reactions. It was found that the termolecular mechanism of SO3 hydration proposed earlier by Morokuma and Muguruma is in good agreement with the experimental rate constants. However, none of the proposed molecular pathways of SOCl2 hydrolysis can provide the high reaction rate observed exp...

Laboratory-made snow doped with either hydrogen peroxide (H2O2) or formaldehyde (HCHO) was exposed to radiation in the ultraviolet and visible range, resulting in a decomposition of both compounds. These experiments demonstrate that, besides the photolysis of nitrate, further photochemical reactions of atmospheric relevant compounds can take place in snow. Under similar conditions the decomposition of H2O2 is more efficient than that of HCHO. Since the decompositions in the experiments follow first-order reaction kinetics, we suggest that the same products as in photolysis reactions in the liquid phase are produced. If similar reactions also take place in natural snow covers, these reactions would have several important consequences. The reactions could represent pathways for the generation of highly reactive radicals in the condensed phase, enhancing the photochemical activity of surface snow and modifying the oxidation capacity of the atmospheric boundary layer. The photolysis could also constitute an additional sink for H2O2 and HCHO in surface snow, which should be taken into account for the reconstruction of atmospheric concentrations of both compounds from concentration profiles in surface snow and ice cores.

The reflection–absorption FTIR spectra of the ozone–water films deposited on a cold metallic surface at 80 K before and after irradiation at 250 and 320 nm were studied to model the ozone photolysis and superoxidant adsorption taking place on the ice particles in the Earth's atmosphere. A new sharp intense band at 2860 cm−1 and a low-intense band at 1450 cm−1 were observed after irradiation at both wavelengths together with remarkable reshaping of the ice Ih bands in the regions 3100–3600 cm−1 and 500–1000 cm−1. The annealing of the reaction mixture has small effect on the intensities and positions of the new bands. The adsorption of formed species was modelled by DFT cluster calculations. The species O(1D), O(3P), O2(a 1Δg), O2(X 3Σg), HO˙, HOO˙, H2O2 were considered as possible intermediates and products. Among them, HO˙, H2O2, and HOO˙, form hydrogen bound complexes with estimated binding energies of −17.6, −28.5, and −37.2 kJ mol−1, correspondingly. The observed IR band of 2860 cm−1 can not be assigned to the OH vibrations of H2O2 shifted due to the adsorption and it is assigned to the ν2 + ν6 combination band of H2O2. Apart from H2O2, two other species can absorb in the region 2700–2900 cm−1: the adsorption complex of HOO˙ on the ice surface and O(1D) forming the complex with the ice of oxywater structure O⋯OH2 stabilized by additional hydrogen bonds.

It has been shown that NOx is produced photochemically within the snowpack of polar regions. If emitted to the atmosphere, this process could be a major source of NOx in remote snowcovered regions. We report here on measurements made at the German Antarctic station, Neumayer, during austral summer 1999, aimed at detecting and quantifying emissions of NOx from the surface snow. Gradients of NOx measured, and fluxes calculated using local meteorology measurements. On the 2 days of flux measurements, the derived fluxes showed continual release from the snow surface, varying between ∼0 and 3 × 108 molecs/cm²/s. When not subject to turbulence, the variation was coincident with the uv diurnal cycle, suggesting rapid release once photochemically produced. Scaling the diurnal average of Feb. 7th (1.3 × 108 molecs/cm²/s) suggests an annual emission over Antarctica of the order 0.0076TgN.

The annual cycles of hydrogen peroxide (H2O2) and methylhydroperoxide (MHP) have been investigated at a remote site in Antarctica in order to study seasonal variations as well as chemical processes in the troposphere. The measurements have been performed from March 1997 to January 1998 and in February 1999 at the German Antarctic research station Neumayer which is located at 70°39S, 8°15W. The obtained time series for hydrogen peroxide and methylhydroperoxide in near-surface air represents the first all-year measurements in Antarctica and indicates clearly the occurrence of seasonal variations. During polar night mean values of 0.054 ± 0.046 ppbv (range

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.

The formation of binary complexes of sulfuric acid with hydrogen chloride, water, nitric acid, chlorine nitrate, and hydrogen peroxide has been investigated by means of ab initio calculations at the Hartree−Fock and MP2 levels of theory. The hydrogen bonds for the complexes with water, hydrogen peroxide, and nitric acid are found to be strong, whereas hydrogen chloride and chlorine nitrate form only weak complexes. For the first time, structural data for binary complexes of sulfuric acid with hydrogen chloride, nitric acid, chlorine nitrate, and hydrogen peroxide have been obtained. The geometry of the calculated sulfuric acid/water complex with the highest stability is in good agreement with the available data in the literature. The stability of the sulfuric acid complexes with hydrogen peroxide and nitric acid are indications that these gases may also take part in the nucleation process of stratospheric sulfuric acid aerosol.

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 reversible photoinitiated isomerization reaction of BrOBr to BrBrO was measured in solid argon matrixes and calculated by multiconfigurational quasidegenerate perturbation theory (MCQDPT). The calculated vertical excitation energies are in good agreement with the experimentally observed excitation wavelengths. While the isomerization from BrOBr to BrBrO appears to be quantitative, some product loss is observed during the back reaction. The calculated excitation energies and oscillator strengths for transitions from the ground to excited states offer a detailed explanation of this behavior.

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.

Measurements have been performed to study the origin of the tropospheric nighttime concentrations of HNO2 The experiments were carried out at three locations with different levels of pollution by using a commercial differential optical absorption spectroscopy (DOAS) and a point sampling analyser. The DOAS observations allowed study of the concentrations of HNO2, NO2, SO2 and O3. Light intensities given by the DOAS system were used to estimate rough values for the total surface of aerosols S along the beam path. NO was measured by a chemiluminescent monitor. A HNO2 formation is clearly indicated by the nighttime increase of the HNO2/NOx ratio. Correlation studies suggest the participation of the aerosol surface in the heterogeneous formation in the less polluted areas. In Milan the measured HNO2 concentrations are considered to be influenced by the nighttime boundary layer and the heterogeneous formation on permanent surfaces like buildings.

The reaction O( 1 D) + CF 3 Br has been investigated in solid Ar-matrices at T = 14 K. Codeposition of O 3 /CF 3 Br/Ar mixtures and irradiation at 250 nm yielded F 2 CO as dominant reaction product. Experiments with 18 O 3 indicate that CF 3 OBr was formed during the course of the reaction. Our observations were interpreted with the formation of an excited CF 3 OBr molecule which can be stabilized in the matrix cage or decompose rapidly into two different F 2 CO·HF complexes.

A high-resolution FTIR spectrometer has been installed at Spitsbergen (79°N) in the German Arctic research station (Koldewey station) in order to measure atmospheric trace gases at high latitudes. For these ground-based absorption measurements either the sun or the moon are used as infrared light source depending on the time of the year. From the obtained spectra it is possible to retrieve the zenith total column densities of more than 20 trace gases in the troposphere and stratosphere. Furthermore, high-resolution spectra provide information on the vertical concentration profile. Seasonal variations of trace gas concentrations in the north polar atmosphere have been studied to get information about chemical and dynamical processes which could be responsible for stratospheric ozone depletion.

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.

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.

The IR spectra of the complexes between dimethylether (DME) and hydrogen iodide in nitrogen matrices were reinvestigated with careful attention to the temperature and IR radiation effects upon the higher aggregates. Irradiation using a broad band IR source was found weakly active leading to a nearly stationary population of the two (DME) 2 H + I − species. Irradiation with CO 2 laser lines induced a conformational interconversion of both aggregates to non-hydrogen-bonded forms. The breaking of the strong hydrogen bond was principally governed by irradiation in the range 2600-1500 cm −1 corresponding to the δ CH 3 region whereas the reverse process was observed by increasing temperature above 27 K under the annealing limit or irradiation below 1100 cm −1 . No accurate evidence was found for the occurrence of photochemical proton transfer between the centrosymmetrical and asymmetrical cations characterizing the two investigated complexes.

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.

The results of a combined vibrational and structural study of the (E)-crotonic acid monomer undertaken by matrix-isolated low-temperature IR spectroscopy and ab initio SCF-MO calculations are presented. It is shown that in both argon and krypton matrices monomeric (E)-crotonic acid exists as a mixture of two conformers of similar energies, differing by the relative orientation of the CC—CO axis (the s-cis and s-trans forms, having a CC—CO dihedral angle equal to 0° and 180°, respectively). Upon UV-irradiation in the 240–250 nm region by a xenon lamp, photoisomerization reactions about both Cα—C and CC bonds occur leading, respectively, to s-cis→ s-trans(E)-crotonic acid rotamerization and (E)-crotonic acid →(Z)-crotonic acid conversion. Results of ab initio SCF-MO calculations, in particular optimized geometries, relative stabilities, dipole moments and harmonic force fields, for the relevant conformational states of both (E) and (Z)-crotonic acids are also presented and the conformational dependence of some relevant structural parameters is used to characterize the most important intramolecular interactions present in the studied forms. Finally, results of a normal mode analysis based on the ab initio calculated vibrational spectra are used to help interpret the experimenal vibrational data, enabling a detailed assignment of the matrix-isolated spectra and the characterization of the observed photoinduced isomerization reactions.

The formation of binary complexes of sulfuric acid with hydrogen chloride, water, nitric acid, chlorine nitrate, and hydrogen peroxide has been investigated by means of ab initio calculations at the Hartree−Fock and MP2 levels of theory. The hydrogen bonds for the complexes with water, hydrogen peroxide, and nitric acid are found to be strong, whereas hydrogen chloride and chlorine nitrate form only weak complexes. For the first time, structural data for binary complexes of sulfuric acid with hydrogen chloride, nitric acid, chlorine nitrate, and hydrogen peroxide have been obtained. The geometry of the calculated sulfuric acid/water complex with the highest stability is in good agreement with the available data in the literature. The stability of the sulfuric acid complexes with hydrogen peroxide and nitric acid are indications that these gases may also take part in the nucleation process of stratospheric sulfuric acid aerosol.

Total column concentrations and volume mixing ratio profiles of methane have been retrieved from ground-based solar absorption FTIR spectra in the near-infrared recorded in Paramaribo (Suriname). The methane FTIR observations are compared with TM5 model simulations and satellite observations from SCIAMACHY, and represent the first validation of SCIAMACHY retrievals in the tropics using ground-based remote sensing techniques. Apart from local biomass burning features, our methane FTIR observations agree well with the SCIAMACHY retrievals and TM5 model simulations.

Laboratory studies have been carried out with the aim to improve our understanding of physicochemical processes which take place at the water ice/air interface initiated by solar irradiation with a wavelength of 121.6 nm. It was intended to mimic the processes of ice particles characteristic of Noctilucent Clouds (NLCs). The experimental set-up used includes a high-vacuum chamber, a gas handling system, a cryostat with temperature controller, an FTIR spectrometer, a vacuum ultraviolet hydrogen lamp, and a microwave generator. We report the first results of measurements of the absolute photodesorption rate (loss of substance due to the escape of photoproducts into gas phase) from thin (20–100 nm) water ice samples kept in the temperature range of 120–150 K. The obtained results show that a flow of photoproducts into the gas phase is considerably lower than presumed in the recent study by Murray and Plane (2005). The experiments indicate that almost all photoproducts remain in the solid phase, and the principal chemical reaction between them is the recombination reaction H + OH → H2O which is evidently very fast. This means that direct photolysis of mesospheric ice particles seems to have no significant impact on the gas phase chemistry of the upper mesosphere.

Total column concentrations of methane have been retrieved from ground-based solar absorption FTIR spectra in the near-infrared recorded in Paramaribo (Suriname). The methane FTIR observations are compared with TM5 model simulations and satellite observations from SCIAMACHY, and represent the first validation of SCIAMACHY retrievals in the inner tropics using ground-based remote sensing techniques. Apart from local biomass burning features, our methane FTIR observations agree well with TM5 model simulations. The comparison of the direct measured CH4/CO2 ratios by FTIR and satellite reveals that the satellite can hardly detect methane emissions of tropical biomass burning due to the used retrieval method.

Field measurements have been performed to study the influence of heterogeneous processes on the trace gas concentration of HNO2 and CH2O in the atmosphere. The observations indicate that during foggy episodes HNO2 is formed to a high extent when NO, NO2 and aerosols are present simultaneously. Far more CH2O is found to be dissolved in the aerosol droplets than what is expected from the literature value of the Henry constant.

Photooxidations of CH3Cl, CH3Br, CF3Br, and CHBr3 with dry-air have been investigated at 298 K in a static reaction vessel by means of FTIR spectroscopy. Irradiation of the reaction mixtures has been performed by Hg-resonance lamps (184.9 nm and 253.7 nm lines) and broad band UV-fluorescence lamps (300-400 nm). The photooxidation mechanism of CH3Cl and CH3Br is governed by two different pathways: 1) photolytical release of halogen atoms and subsequent oxidation of the CH3 radical, 2) abstraction of an H-atom and oxidation of the respective CH2Cl and CH2Br-fragment. The second path leads to the formation of the formyl-halides HClCO and HBrCO which are tranferred to CO and HCl or CO and HBr, respectively. Addition of trace amounts of NO to the gas mixture decreases the HClCO yield strongly. We suggest that NO reacts with the transient H2ClCO-radical to ClNO + H2CO. HBrCO, Br2CO and the final products CO, CO2, and HBr could be identified after Hg-resonance lamps induced photooxidation of CHBr3. The Cl2/fluorescence lamps induced photooxidation, however, yielded solely Br2CO, CO2, and HBr. In contrast to the labile species HClCO, HBrCO, and Br2CO, the photooxidation product of CF3Br, carbonyl fluoride (F2CO) is relatively inert under our reaction conditions.

Photooxidation of carbonyl sulfide (SCO) in the presence of ozone has been studied in solid argon matrices under stratospheric irradiation conditions. The matrix experiments allowed the isolation and identification of SCO.O3 1:1 aggregates. Selective photolysis of O3 yielded O(1D) atoms and subsequent reaction with SCO resulted in the primary formation of CO2 + S. The sulfur atoms generated this way are oxidized to SO2 by O2, which has been formed during photofragmentation of O3. In further steps SO2 reacted with diffusing O atoms to SO3 and SO4. Experiments with isotopically labeled precursors confirmed the conclusions that the photolysis of 18O3.SCO hetero-complexes leads to S18O2, S18O3, and 16OC18O formation.

Volatile inorganic and size-resolved particulate Cl- and Br-species were measured in near-surface air over a broad range of conditions within four distinct regimes (European – EURO, North African – N-AFR, the Intertropical Convergence Zone – ITCZ, and South Atlantic – S-ATL) along a latitudinal gradient from 51° N to 18° S through the eastern Atlantic Ocean. Median dry-deposition fluxes of sea salt, oxidized N, and oxidized non-sea-salt S varied by factors of 25, 17, and 9, respectively, among the regimes. Sea-salt production was the primary source for inorganic Cl and Br. Acidification and dechlorination of sea salt primarily by HNO3 sustained HCl mixing ratios ranging from medians of 82 (ITCZ) to 682 (EURO) pmol mol−1. Median aerosol pHs inferred from HCl phase partitioning with super-μm size fractions ranged from ~3.0 for EURO to ~4.5 for ITCZ. Because SO2 solubility over this pH range was low, S(IV) oxidation by hypohalous acids was unimportant under most conditions. Simulations with a detailed multiphase box model indicated that BrCl photolysis and ClO + NO were the major sources for atomic Cl in all regimes. Simulated midday concentrations of Cl atoms ranged from 2.1×104 to 7.8×104 cm−3 in the ITCZ and N-AFR regimes, respectively. Measured particulate Br− (median enrichment factor = 0.25) was greater and volatile inorganic Br less than simulated values, suggesting that the halogen activation mechanism in the model overestimated Br-radical production and processing. Reaction with atomic Br was an important sink for modeled O3 (5% in EURO to 46% in N-AFR). Formation of halogen nitrates accelerated the oxidation of NOx (NO + NO2) primarily via hydrolysis reactions involving S aerosol. Relative to simulations with no halogens, lower NOx coupled with direct reactions involving halogens yielded lower steady state mixing ratios of OH (20% to 54%) and O3 (22% to 62%) and lower midday ratios of OH:HO2 (3% to 32%) in all regimes.

The standard enthalpies, entropies, and Gibbs free energies of separate stages of the multistep hydrolysis of MX 4 molecules (M = C, Si, Ge; X = H, F, Cl) in the gas phase at 298 K were calculated by the G3 high-precision quantum-chemical method of calculation of thermodynamic parameters. The trends in these parameters were analyzed for each group of molecules. The calculated thermodynamic parameters make it pos- sible to estimate the theoretical limits for the contents of water and hydrolysis products in the above high-purity carbon, silicon, and germanium derivatives.

Infrared spectra are reported for binary complexes between perfluoro-tert-butanol as proton donor and nitromethane and acetone as bases. The complexes have been investigated in low temperature solutions and in cryogenic matrices. The spectra have been evaluated in terms of frequency shifts (ΔVOH), half widths (FWHH) and anharmonicities (κ) caused by the hydrogen bonding of these complexes. The influence of the environment (solvents and solid matrices) as well as temperature on the spectra of the complexes has also been studied and is discussed in detail. Key words: hydrogen bonding, temperature effects, solutions, matrix.

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.

[1] We present the first ground-based solar absorption Fourier Transform Infrared (FTIR) spectrometric measurements in the inner tropics over several years. The FTIR observations agree well with satellite data from the MOPITT instrument. MATCH-MPIC model simulations reproduce the mean vertical structure of the FTIR observations. The model is generally not able to reproduce the extreme enhancements seen during the specific biomass burning events by both observation instruments. Nevertheless, the model indicates that beyond the background source of CO from methane oxidation, the main contributions to the CO mixing ratios are the episodic convective injection of NMHCs and CO from South American biomass burning into the upper troposphere, along with long range transport of African biomass burning CO, particularly during spring. In future studies with more extensive observed time series, observations such as these will be valuable for evaluating ongoing improvements in global chemistry transport models.

Ship-borne measurements of spectral as well as biologically effective UV irradiance have been performed on the German research vessel Polarstern during the Atlantic transect from Bremerhaven, Germany (53.5 degrees N, 8.5 degrees E), to Cape Town, South Africa (33.6 degrees S, 18.3 degrees E), from 13 October to 17 November 2005. Such measurements are required to study UV effects on marine organisms. They are also necessary to validate satellite-derived surface UV irradiance. Cloud free radiative transfer calculations support the investigation of this latitudinal dependence. Input parameters, such as total ozone column and aerosol optical depth have been measured on board as well. Using these measured parameters, the modelled cloudless noontime UVA irradiance (320-400 nm) shows the expected dependence on varying minimum solar zenith angles (SZA) at different latitudes. The modelled cloudless noontime UVB irradiance (290-320 nm) does not show this clear dependence on SZA due to the strong influence of ozone absorption in this spectral range. The maximum daily dose of erythemal irradiance of 5420 J m(-1) was observed on 14 November 2005, when the ship was in the tropical Atlantic south of the equator. The expected UV maximum should have been observed with the sun in the zenith during local noon (11 November). Stratiform clouds reduced the dose to 3835 J m(-1). In comparison, the daily erythemal doses in the mid-latitudinal Bay of Biscay only reached values between 410 and 980 J m(-1) depending on cloud conditions. The deviation in daily erythemal dose derived from different instruments is around 5%. The feasibility to perform ship-borne measurements of spectral UV irradiance is demonstrated.

The snow and iceshields of the polar regions serve as a climate archiveand deliver a useful insight back to about 250.000 years of earth climatehistory1,2. The aim of our investigation reported here was to establisha new method for the determination of trace elements in ice cores frompolar regions with Laserablation Inductively Coupled Plasma MassSpectrometry (LA-ICP-MS)3. Primarily, the construction of a cryogeniclaserablation chamber and the optimization of the analysis system forthe sample matrix were the main goals. This paper reports preliminaryresults from measurements of frozen ice samples, the achievable signalintensities, standard deviations and calibration graphs as well as the firstsignal progression of 208Pb in an 8000 years old ice core sample fromGreenland.

We present long-term time-series of strato-mesospheric CO vertical columns measured from stations located in Antarctica, mid-latitudes and the Arctic, covering the period from 1997–2005. The instrument and the measurement technique allows the separation of tropospheric and strato-mesospheric contributions to the CO column, therefore providing information on the chemistry and dynamics both at low and high altitudes. Data from polar stations show a similar annual variability of strato-mesospheric CO with a strong maximum in late winter and spring and a small enhancement in late summer for some stations, which we call the "summer bulge''. Generally, the mid-latitude stations show no significant annual variability of strato-mesospheric CO columns. Measurements were compared with a two-dimensional chemistry-transport model of the middle atmosphere. The annual and latitudinal variations of CO are reproduced very well by a model run including thermospheric CO. Comparison with different model scenarios show that the polar winter maximum is due solely to downward transport of thermospheric CO, while the summer maximum is due to CHOx chemistry in the stratosphere.

With a lidar system that was installed in Lindenberg/Germany, we observed in June 2003 an extended aerosol layer at 13km altitude in the lowermost stratosphere. This layer created an inelastic backscatter signal that we detected with a water vapour Raman channel, but that was not produced by Raman scattering. Also, we find evidence for inelastic scattering from a smoke plume from a forest fire that we observed in the troposphere. We interpret the unexpected properties of these aerosols as fluorescence induced by the laser beam at organic components of the aerosol particles. Fluorescence from ambient aerosol had not yet been considered detectable by lidar systems. However, organic compounds such as polycyclic aromatic hydrocarbons sticking to the aerosol particles, or bioaerosol such as bacteria, spores or pollen fluoresce when excited with UV-radiation in a way that is detectable by our lidar system. Therefore, we conclude that fluorescence from organic material released by biomass burning creates, inelastic backscatter signals that we measured with our instrument and thus demonstrate a new and powerful way to characterize aerosols by a remote sensing technique. The stratospheric aerosol layer that we have observed in Lindenberg for three consecutive days is likely to be a remnant from Siberian forest fire plumes lifted across the tropopause and transported around the globe.