bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainties and assessments of chemistry-climate models of the stratosphere
Authors: Austin J. , Shindell D. , Beagley S. R. , Brühl C. , Dameris M. , Manzini E. , Nagashima T. , Newman P. , Pawson S. , Pitari G. , Rozanov E. , Schnadt C. , Shepherd T. G.
Published: April 2010

Abstract. In recent years a number of chemistry-climate models have been developed with an emphasis on the stratosphere. Such models cover a wide range of timescales of integration and vary considerably in complexity. The results of specific diagnostics are here analysed to examine the differences amongst individual models and observations, to assess the consistency of model predictions, with a particular focus on polar ozone. For example, many models indicate a significant cold bias in high latitudes, the 'cold pole problem', particularly in the southern hemisphere during winter and spring. This is related to wave propagation from the troposphere which can be improved by improving model horizontal resolution and with the use of non-orographic gravity wave drag. As a result of the widely differing modeled polar temperatures, different amounts of polar stratospheric clouds are simulated which in turn result in varying ozone values in the models. The results are also compared to determine the possible future behaviour of ozone, with an emphasis on the polar regions and mid-latitudes. All models predict eventual ozone recovery, but give a range of results concerning its timing and extent. Differences in the simulation of gravity waves and planetary waves as well as model resolution are likely major sources of uncertainty for this issue. In the Antarctic, the ozone hole has probably reached almost its deepest although the vertical and horizontal extent of depletion may increase slightly further over the next few years. According to the model results, Antarctic ozone recovery could begin any year within the range 2001 to 2008. For the Arctic, most models indicate that small ozone losses may continue for a few more years and that recovery could begin any year within the range 2004 to 2019. The start of ozone recovery in the Arctic is therefore expected to appear later than in the Antarctic in most models. Further, interannual variability will tend to mask the signal for longer in the Arctic than in the Antarctic, delaying still further the date at which ozone recovery may be said to have started. In the longer term, the model results suggest that full recovery of ozone to 1980 levels is not expected in the Antarctic until about the year 2050. Earlier recovery to 1980 levels may be possible in the Arctic, but model differences are too large compared with the simulated changes to obtain a reliable date.
Uptake and reaction of HOBr on frozen and dry NaCl/NaBr surfaces between 253 and 233K
Authors: Adams J. W. , Holmes N. S. , Crowley J. N.
Published: April 2010

Abstract. The uptake and reaction of HOBr with frozen salt surfaces of variable NaCl / NaBr composition and temperature were investigated with a coated wall flow tube reactor coupled to a mass spectrometer for gas-phase analysis. HOBr is efficiently taken up onto the frozen surfaces at temperatures between 253 and 233 K where it reacts to form the di-halogens BrCl and Br2, which are subsequently released into the gas-phase. The uptake coefficient for HOBr reacting with a frozen, mixed salt surface of similar composition to sea-spray was approx. 10-2. The relative concentration of BrCl and Br2 released to the gas-phase was found to be strongly dependent on the ratio of Cl - to Br - in the solution prior to freezing / drying. For a mixed salt surface of similar composition to sea-spray the major product at low conversion of surface reactants (i.e. Br - and Cl -) was Br2. Variation of the pH of the NaCl / NaBr solution used to prepare the frozen surfaces was found to have no significant influence on the results. The observations are explained in terms of initial formation of BrCl in a surface reaction of HOBr with Cl -, and conversion of BrCl to Br2 via reaction of surface Br -. Experiments on the uptake and reaction of BrCl with frozen NaCl / NaBr solutions served to confirm this hypothesis. The kinetics and products of the interactions of BrCl, Br2 and Cl2 with frozen salt surfaces were also investigated, and lower limits to the uptake coefficients of > 0.034, >0.025 and >0.028 respectively, were obtained. The uptake and reaction of HOBr on dry salt surfaces was also investigated and the results closely resemble those obtained for frozen surfaces. During the course of this study the gas diffusion coefficients of HOBr in He and H2O were also measured as (273 ± 1) Torr cm2 s-1 and (51 ± 1) Torr cm2 s-1, respectively, at 255 K. The implications of these results for modelling the chemistry of the Arctic boundary layer in springtime are discussed.
Application of the Spectral Structure Parameterization technique: retrieval of total water vapor columns from GOME
Authors: Lang R. , Williams J. E. , van der Zande W. J. , Maurellis A. N.
Published: April 2010

Abstract. We use a recently proposed spectral sampling technique for measurements of atmospheric transmissions called the Spectral Structure Parameterization (SSP) in order to retrieve total water vapor columns (WVC) from reflectivity spectra measured by the Global Ozone Monitoring Experiment (GOME). SSP provides a good compromise between efficiency and speed when performing retrievals on highly structured spectra of narrow-band absorbers like water vapor. We show that SSP can be implemented in a radiative transfer scheme which treats both direct-path absorption and absorption by singly scattered light directly. For the retrieval we exploit a ro-vibrational overtone band of water vapor located in the visible around 590 nm. We compare our results to independent values given by the data assimilation model of ECMWF. In addition, results are compared to those obtained from the more accurate, but slower, Optical Absorption Coefficient Spectroscopy (OACS).
Comparison of total ozone from the satellite instruments GOME and TOMS with measurements from the Dobson network 1996–2000
Authors: Bramstedt K. , Gleason J. , Loyola D. , Thomas W. , Bracher A. , Weber M. , Burrows J. P.
Published: April 2010

Abstract. Over the last 3 decades, satellite data have been used to monitor long-term global changes in stratospheric ozone. The TOMS series (1978 -- present) and GOME (1995 -- present) are two very important instruments in this context. In this paper, TOMS total ozone and three approaches to derive total ozone from GOME measurements are validated with ground-based Dobson network data. Beyond the operational products of both instruments, e.g. TOMS Version 7 and GOME Data Processor Version 2.7, total ozone is calculated by integrating FURM ozone profiles and by applying the TOMS algorithm to the GOME spectra. All algorithms show in general good agreement with ground-based measurements. The operational GOME total ozone shows seasonal variations, most likely introduced by difficulties in the derivation of airmass factors, which convert measured slant columns into vertical columns. The TOMS algorithm estimates on average 2% higher total ozone in the southern hemisphere than in the northern for both instruments as compared to the ground-based data, indicating that the source of the observed hemispheric differences is in the TOMS algorithm. Both instruments show aging effects in 2000, leading to enhanced variability in the ozone column differences with respect to Dobson data. In addition, the integrated GOME ozone profiles and the TOMS algorithm applied to GOME data show larger mean deviations in 2000.
Influence of spectral solar irradiance on the formation of new particles in the continental boundary layer
Authors: Boy M. , Kulmala M.
Published: April 2010

Abstract. The relationship between nucleation events and spectral solar irradiance was analysed using two years of data collected at the Station for Measuring Forest Ecosystem-Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. We analysed the data in two different ways. In the first step we calculated ten nanometer average values from the irradiance measurements between 280 and 580 nm and explored if any special wavelengths groups showed higher values on event days compared to a spectral reference curve for all the days for 2 years or to reference curves for every month. The results indicated that short wavelength irradiance between 300 and 340 nm is higher on event days in winter (February and March) compared to the monthly reference graph but quantitative much smaller than in spring or summer. By building the ratio between the average values of different event classes and the yearly reference graph we obtained peaks between 1.17 and 1.6 in the short wavelength range (300--340 nm). In the next step we included number concentrations of particles between 3 and 10 nm and calculated correlation coefficients between the different wavelengths groups and the particles. The results were quite similar to those obtained previously; the highest correlation coefficients were reached for the spectral irradiance groups 3--5 (300--330 nm) with average values for the single event classes around 0.6 and a nearly linear decrease towards higher wavelengths groups by 30%. Both analyses indicate quite clearly that short wavelength irradiance between 300 and 330 or 340 nm is the most important solar spectral radiation for the formation of newly formed aerosols. In the end we introduce a photochemical mechanism as the probable responsible pathway by calculating the production rate of excited oxygen. This mechanism shows in which way short wavelength irradiance can influence the formation of new particles even though the absolute values are one to two magnitudes smaller compared to irradiance between 400 and 500 nm.
The potential of polarization measurements from space at mm and sub-mm wavelengths for determining cirrus cloud parameters
Authors: Miao J. , Johnsen K.-P. , Buehler S. , Kokhanovsky A.
Published: April 2010

Abstract. The millimeter and sub-millimeter waves have been attracting a lot of attention recently in the cloud remote sensing community. This is largely because of its potential use in measuring cirrus cloud parameters with airborne or space-borne radiometers. In this study, we examine the possibility of using polarization measurements in this frequency range to retrieve microphysical parameters of cloud ice particles. By using a simple radiative transfer model, the polarization differences of the brightness temperatures measured at the vertical and horizontal polarization channels are calculated at the following seven frequencies: 90, 157, 220, 340, 463, 683, and 874 GHz. The cirrus clouds are modeled with nearly spherical particles, circular cylinder, and circular plate, as well as with mixtures of these types. We found that the polarization difference shows a unique ``resonance'' feature with the change of ice particle characteristic size: it has a strong response only in a certain range of ice particle size, beyond that range it approaches zero. The size range where this resonance happens depends to a large extent on particle shape and aspect ratio, but to a much less extent on particle orientation. This resonance feature remains even when the particles are mixed with different shapes, although the magnitude and the position of the resonance peak may change, depending on how ice particles are mixed. Oriented particles generally show larger polarization difference than randomly oriented ones, and plates have larger polarization difference than cylinders. However, particle orientations have a significantly stronger influence on the polarization difference than particle shapes (cylinder or plate). This makes it difficult to distinguish particle shapes using millimeter and sub-millimeter radiometric measurements, if there is no information available on particle orientations. However, if the state of particle shape mixture can be predetermined by other approaches, polarization measurements can help to determine ice particle characteristic size and orientation. This information, in turn, will benefit the retrieval of cloud ice water path.
Numerical simulations of homogeneous freezing processes in the aerosol chamber AIDA
Authors: Haag W. , Kärcher B. , Schaefers S. , Stetzer O. , Möhler O. , Schurath U. , Krämer M. , Schiller C.
Published: April 2010

Abstract. The homogeneous freezing of supercooled H2SO4/H2O aerosols in an aerosol chamber is investigated with a microphysical box model using the activity parameterization of the nucleation rate by Koop et al (2000). The simulations are constrained by measurements of pressure, temperature, total water mixing ratio, and the initial aerosol size distribution, described in a companion paper Möhler et al. (2002). Model results are compared to measurements conducted in the temperature range between 194 and 235 K, with cooling rates in the range between 0.5 and 2.6 K min-1, and at air pressures between 170 and 1000 hPa. The simulations focus on the time history of relative humidity with respect to ice, aerosol size distribution, partitioning of water between gas and particle phase, onset times of freezing, freezing threshold relative humidities, aerosol chemical composition at the onset of freezing, and the number of nucleated ice crystals. The latter three parameters can directly be inferred from the experiments, the former three aid in interpreting the measurements. Sensitivity studies are carried out to address the relative importance of uncertainties of basic quantities such as temperature, H2O mixing ratio, aerosol size spectrum, and deposition coefficient of H2O molecules on ice. The ability of the numerical simulations to provide detailed explanations of the observations greatly increases confidence in attempts to model this process under real  atmospheric conditions, for instance with regard to the formation of cirrus clouds or type-II polar stratospheric clouds, provided that accurate temperature and humidity measurements are available.
In situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses
Authors: Seifert M. , Ström J. , Krejci R. , Minikin A. , Petzold A. , Gayet J.-F. , Schumann U. , Ovarlez J.
Published: April 2010

Abstract. In situ observations of aerosol particles contained in cirrus crystals are presented and compared to interstitial aerosol size distributions (non-activated particles in between the cirrus crystals). The observations were conducted in cirrus clouds in the Southern and Northern Hemisphere mid-latitudes during the INCA project. The first campaign in March and April 2000 was performed from Punta Arenas, Chile (54° S) in pristine air. The second campaign in September and October 2000 was performed from Prestwick, Scotland (53° N) in the vicinity of the North Atlantic flight corridor. Size distribution measurements of crystal residuals (particles remaining after evaporation of the crystals) show that small aerosol particles (Dp < 0.1µm) dominate the number density of residuals. The crystal residual size distributions were significantly different in the two campaigns. On average the residual size distributions were shifted towards larger sizes in the Southern Hemisphere. For a given integral residual number density, the calculated particle volume was on average three times larger in the Southern Hemisphere. This may be of significance to the vertical redistribution of aerosol mass by clouds in the tropopause region. In both campaigns the mean residual size increased with increasing crystal number density. The observations of ambient aerosol particles were consistent with the expected higher pollution level in the Northern Hemisphere. The fraction of residual particles only contributes to approximately a percent or less of the total number of particles, which is the sum of the residual and interstitial particles.
The H Lyman-α actinic flux in the middle atmosphere
Authors: Reddmann Th. , Uhl R.
Published: April 2010

Abstract. The penetration of solar H Lyman-a radiation into the terrestrial middle atmosphere is studied in detail. The Lyman-a actinic flux is calculated with a Monte Carlo approach including multiple resonance scattering of Lyman-a photons within the terrestrial atmosphere and a temperature dependent absorption cross section of molecular oxygen. The dependence of the actinic flux on the temperature profile is significant for O2 column densities greater than about 1024 m-2. For column densities greater than about 5 · 1024 m-2 resonance scattering becomes important at solar zenith angles > 60°. The \\OD\\ quantum yield of the O2 dissociation by Lyman-aphotons is found to decrease from 0.58 in the lower thermosphere to 0.48 in the lower mesosphere. Parameterisations for Lyman-a actinic flux, mean O2 absorption cross section and \\OD\\quantum yield including temperature dependence and resonance scattering are given valid up to a O2 column density of about 1025 m-2.
Long term measurements of submicrometer urban aerosols: statistical analysis for correlations with meteorological conditions and trace gases
Authors: Wehner B. , Wiedensohler A.
Published: April 2010

Abstract. Long-term measurements (over 4 years) of particle number size distributions (submicrometer particles, 3--800 nm in diameter), trace gases (NO, NO2, and O3), and meteorological parameters (global radiation, wind speed and direction, atmospheric pressure, etc.) were taken in a moderately polluted site in the city of Leipzig (Germany). The resulting complex data set was analyzed with respect to seasonal, weekly, and diurnal variation of the submicrometer aerosol. Car traffic produced a peak in the number size distribution at around 30 nm particle diameter during morning rush hour on weekdays. A second peak at 10--15 nm particle diameter occurred around noon during summer, confirmed by high correlation between concentration of particles less than 20 nm and the global radiation. This new-particle formation at noon was correlated with the amount of global radiation. A high concentration of accumulation mode particles (between 100 and 800 nm), which are associated with large particle-surface area, might prevent this formation. Such high particle concentration in the ultrafine region (particles smaller than 20 nm in diameter) was not detected in the particle mass, and thus, particle mass concentration is not suitable for determining the diurnal patterns of particles. In summer, statistical time series analysis showed a cyclic pattern of ultrafine particles with a period of one day and confirmed the correlation with global radiation. Principal component analysis (PCA) revealed a strong correlation between the particle concentration for 20 -- 800 nm particles and the NO- and NO2-concentrations, indicating the influence of combustion processes on this broad size range, in particular during winter. In addition, PCA also revealed that particle concentration depended on meteorological conditions such as wind speed and wind direction, although the dependence differed with particle size class.
Reply to: “Tropical cirrus and water vapor: an effective Earth infrared iris feedback?"
Authors: Chou M.-D. , Lindzen R. S. , Hou A. Y.
Published: April 2010

Abstract. In assessing the iris effect suggested by Lindzen et al. (2001), Fu et al. (2001, 2002) found that the response of high-level clouds to the sea surface temperature had an effect of reducing the climate sensitivity to external radiative forcing, but the effect was not as strong as Lindzen et al. (2001) found. The approach of Fu et al. (2001, 2002) to specifying longwave emission and cloud albedos appears to be inappropriate, and the derived cloud optical properties may not have real physical meaning. The cloud albedo calculated by Fu et al. (2001, 2002) is too large for cirrus clouds and too small for boundary layer clouds, which underestimates the iris effect.
A model for particle formation and growth in the atmosphere with molecular resolution in size
Authors: Lehtinen K. E. J. , Kulmala M.
Published: April 2010

Abstract. The formation and growth of atmospheric aerosol particles is considered using an exact discrete method with molecular resolution in size space. The method is immune to numerical diffusion problems that are a nuisance for typical simulation methods using a sectional representation for the particle size distribution. For condensational growth, a slight modification is proposed for the Fuchs-Sutugin expression, which improves the prediction of the growth rate of nano-sized particles by as much as a factor of two. The presented method is applied to particle formation in a Finnish Boreal forest and is shown to capture the essential features of the dynamics quite nicely. Furthermore, it is shown that the growth of the particles is roughly linear, which means that the amount of condensable vapour is constant (of the order 1013 1/m3).
A new actinic flux 4π-spectroradiometer: Instrument design and application to clear sky and broken cloud conditions
Authors: Eckstein E. , Perner D. , Brühl Ch. , Trautmann T.
Published: April 2010

Abstract. A new 4p-spectroradiometer was developed for measuring actinic flux especially under cloudy conditions based on a fixed grating imaging spectrograph and a CCD-detector leading to a simultaneous measurement of the spectrum. The new instrument incorporates a novel optical head with a 4p-field of view independent of angle of incidence. Comparisons with the actinic flux spectroradiometer of the Institute of Atmospheric Chemistry of Forschungszentrum Jülich showed a very good agreement within the limit of the uncertainties of the two instruments. Our spectroradiometer was applied to investigate the effects of broken clouds on the actinic flux and photolysis frequencies on the ground during the BERLIOZ campaign. Reductions as well as enhancements compared to the clear sky case were seen, both effects are larger in the UV-A than the UV-B spectral region. Furthermore the new instrument was used for simultaneous measurements in different altitudes on a tower to study the transmission and attenuation of actinic flux in low clouds. A correlation of attenuation with the simultaneously measured liquid water content of the cloud was found.
The isotopic fingerprint of the pre-industrial and the anthropogenic N2O source
Authors: Röckmann T. , Kaiser J. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. We have performed high-precision measurements of the 18O and position dependent 15N isotopic composition of N2O from Antarctic firn air samples. By comparing these data to simulations carried out with a firn air diffusion model, we have reconstructed the temporal evolution of the N2O isotope signatures since pre-industrial times. The heavy isotope content of atmospheric N2O is presently decreasing for all signatures at rates of about -0.038%o yr -1 for 1d15N, -0.044%o yr -1 for 2d15N and  -0.025%o yr -1 for  d18O. The total decrease since pre-industrial times is estimated to be about -2%o  for  d15N at both positions and -1.2%o  for  d18O. Isotope budget calculations using these trends and recent stratospheric measurements allow to isotopically characterize the present and the pre-industrial global average N2O source, as well as the anthropogenic N2O emissions that have caused the global N2O increase since pre-industrial times. The increased fluxes from the depleted surface sources alone are insufficient to explain the inferred temporal isotope changes. In addition, the global average N2O source signature is calculated to be significantly depleted today relative to the pre-industrial value, in agreement with recent indications from soil emission measurements.
Adjoint backtracking for the verification of the Comprehensive Test Ban Treaty
Authors: Issartel J.-P. , Baverel J.
Published: April 2010

Abstract. An international monitoring system is being built as a verification tool for the Comprehensive Test Ban Treaty. Forty stations will measure on a worldwide daily basis the concentration of radioactive noble gases. The paper introduces, by handling preliminary real data, a new approach of backtracking for the identification of sources after positive measurements. When several measurements are available the ambiguity about possible sources is reduced significantly. As an interesting side result it is shown that diffusion in the passive tracer dispersion equation is necessarily a self-adjoint operator.
On the transition between heterogeneous and homogeneous freezing
Authors: Gierens K.
Published: April 2010

Abstract. Box model simulations of an uplifting and adiabatically cooling cloud of aerosol have been performed in order to study the transition between cirrus formation dominated by homogeneous nucleation of ice to that dominated by heterogeneous nucleation. The aerosol was assumed to consist of an internal mixture of sulfuric acid solution droplets with inclusions of soot. The simulations show that the transition from heterogeneous to homogeneous nucleation occurs over a narrow range of soot concentration. Thus it seems to be possible to fix critical concentrations of heterogeneous ice nuclei which must be exceeded if heterogeneous freezing dominates cirrus formation. A formula has been derived that allows to compute the critical concentrations of heterogeneous ice nuclei as a function of temperature, updraft speed, ambient pressure, and supersaturation at which heterogeneous freezing occurs. Generally, homogeneous nucleation dominates in regions with updrafts stronger than 20 \\cmps, with the exception of heavily polluted areas which could be common in the northern hemisphere due to air traffic, where updrafts of the order 1 \\mps\\ may be necessary to render heterogeneous nucleation unimportant. According to the present results it cannot be excluded that heterogeneous nucleation plays a more important role for cirrus formation in the northern midlatitudes than anywhere else. A possible consequence of these results is that air pollution may lead to a higher coverage of cirrus clouds, but then these clouds will be optically thinner than clouds formed by homogeneous freezing, with the exception of regions where condensation trails are frequent.
Particle formation at a continental background site: comparison of modelresults with observations
Authors: Uhrner U. , Birmili W. , Stratmann F. , Wilck M. , Ackermann I. J. , Berresheim H.
Published: April 2010

Abstract. At Hohenpeissenberg (47°48'N, 11°07'E, 988 m asl), a rural site 200-300 m higher than the surrounding terrain, sulphuric acid concentrations, particle size distributions, and other trace gas concentrations were measured over a two and a half year period. Measured particle number concentrations and inferred particle surface area-concentrations were compared with box-model simulations based on a multimodal lognormal aerosol module that included a binary sulphuric acid water nucleation scheme. The calculated nucleation rates were corrected with a factor to match measured particle number concentrations. These corrections varied over a range of 10-3 - 1017. The correction factors were close to 1 for the measurements made in the winter, which represented stable thermal stratification and low wind conditions. In contrast, the correction factors were the largest for measurements made under strong convective conditions. Our comparison of measured and simulated particle size distributions suggest a distant particle-formation process under convective conditions near the interface of the mixed layer and the entrainment zone, followed by downward transport and particle growth. For stable stratification and low winds, our comparisons suggest that particles formed close to the measurement site.
Observations of large stratospheric ozone variations over Mendoza, Argentina
Authors: Puliafito C. , Enrique Puliafito S. , Hartmann G. K.
Published: April 2010

Abstract. Since November 1993 up to present from Benegas Station, Mendoza, Argentina (site of IEMA Institute) and from high locations in the Andes region, ground based radiometric measurements of stratospheric ozone and tropospheric water vapor have been achieved. Ozone measurements are performed by using a radiometer-spectrometer tuned at 142 GHz and tropospheric water vapor by means of a 92 GHz radiometer. In this paper two case studies of large stratospheric ozone variations due to dynamical processes will be presented. These processes are very likely associated to gravity waves, generated by airflow over the Andes Mountains, or due to Zonda wind effect.
Modeling the chemical effects of ship exhaust in the cloud-free marine boundary layer
Authors: von Glasow R. , Lawrence M. G. , Sander R. , Crutzen P. J.
Published: April 2010

Abstract. The chemical evolution of the exhaust plumes of ocean-going ships in the cloud-free marine boundary layer is examined with a box model. Dilution of the ship plume via entrainment of background air was treated as in studies of aircraft emissions and was found to be a very important process that significantly alters model results. We estimated the chemical lifetime (defined as the time when differences between plume and background air are reduced to 5% or less) of the exhaust plume of a single ship to be 2 days. Increased concentrations of NOx in the plume air lead to higher catalytical photochemical production rates of O3 and also of OH. Due to increased OH concentrations in the plume, the lifetime of many species (especially NOx) is reduced in plume air. The chemistry on background aerosols has a significant effect on gas phase chemistry in the ship plume, while partly soluble ship-produced aerosols are computed to only have a very small effect. Soot particles emitted by ships showed no effect on gas phase chemistry. Halogen species that are released from sea salt aerosols are slightly increased in plume air. In the early plume stages, however, the mixing ratio of BrO is decreased because it reacts rapidly with NO. To study the global effects of ship emissions we used a simple upscaling approach which suggested that the parameterization of ship emissions in global chemistry models as a constant source at the sea surface leads to an overestimation of the effects of ship emissions of roughly a factor of 2. The differences are caused by a strongly reduced lifetime (compared to background air) of NOx in the early stages of a ship plume.
Retrieval methods of effective cloud cover for the GOME instrument: an intercomparison
Authors: Tuinder O. N. E. , de Winter-Sorkina R. , Builtjes P. J. H.
Published: April 2010

Abstract. The radiative scattering by clouds leads to errors in the retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites. Moreover, the presence of clouds changes the UV actinic flux and the photo-dissociation rates of various species significantly. The Global Ozone Monitoring Experiment (GOME) instrument on the ERS-2 satellite, principally designed to retrieve trace gases in the atmosphere is also capable of detecting clouds. Four cloud fraction retrieval methods for GOME data that have been developed are discussed in this paper (the Initial Cloud Fitting Algorithm, the PMD Cloud Retrieval Algorithm, the Optical Cloud Recognition Algorithm and the Fast Retrieval Scheme for Cloud Observables). Their results of cloud fraction retrieval are compared to each-other and also to synoptic surface observations. It is shown that all studied retrieval methods calculate an effective cloud fraction that is related to a cloud with a high optical thickness. Generally, we found ICFA to produce the lowest cloud fractions, followed by OCRA, then FRESCO and PC2K along four processed tracks (+2%, +10% and +15% compared to ICFA respectively). Synoptical surface observations gave the highest absolute cloud fraction when compared with individual PMD sub-pixels of roughly the same size.
Homogeneous nucleation of NAD and NAT in liquid stratospheric aerosols: insufficient to explain denitrification
Authors: Knopf D. A. , Koop T. , Luo B. P. , Weers U. G. , Peter T
Published: April 2010

Abstract. The nucleation of NAD and NAT from HNO3/H2O and HNO3/H2O/H2SO4 solution droplets is investigated both theoretically and experimentally with respect to the formation of polar stratospheric clouds (PSCs). Our analysis shows that homogeneous NAD and NAT nucleation from liquid aerosols is insufficient to explain the number densities of large nitric acid containing particles recently observed in the Arctic stratosphere. This conclusion is based on new droplet freezing experiments employing optical microscopy combined with Raman spectroscopy. The homogeneous nucleation rate coefficients of NAD and NAT in liquid aerosols under polar stratospheric conditions derived from the experiments are < 2 x 10-5 cm-3 s-1 and < 8 x 10-2 cm-3 s-1 , respectively. These nucleation rate coefficients are smaller by orders of magnitude than the value of ~ 103 cm-3 s-1 used in a recent denitrification modelling study that is based on a linear extrapolation of laboratory nucleation data to stratospheric conditions (Tabazadeh et al., Science, 291, 2591--2594, 2001). We show that this linear extrapolation is in disagreement with thermodynamics and experimental data and, therefore, must not be used in microphysical models of PSCs. Our analysis of the experimental data yields maximum hourly production rates of nitric acid hydrate particles per cm3 of air of about 3 x 10-10 cm-3 h-1 under polar stratospheric conditions. Assuming PSC particle production to proceed at this rate for two months we arrive at particle number densities of < 5 x 10-7 cm-3, much smaller than the value of ~ 10-4 cm-3 reported in recent field observations. This clearly shows that homogeneous nucleation of NAD and NAT from liquid supercooled ternary solution aerosols cannot explain the observed polar denitrification.
Twilight tropospheric and stratospheric photodissociation rates derived from balloon borne radiation measurements
Authors: Kylling A. , Danielsen T. , Blumthaler M. , Schreder J. , Johnsen B.
Published: April 2010

Abstract. A new ligthweight multichannel moderate bandwidth filter instrument designed to be flown on balloons, is described. The instrument measures the radiation field within the short UV (center wavelength at 312nm) and long UV (center wavelength at 340nm). The angular and spectral characteristics of the instrument are discussed and the calibration procedure outlined. Measurements made during a stratospheric balloon flight at twilight conditions from Gap-Tallard, France, are presented and compared with state-of-the-art radiative transfer model simulations. The model simulations and the measurements agree within ±10% (±20%) for solar zenith angles smaller than 93° (90°) for the 340 (312)nm channel. Based on the model simulations of the measured radiation, actinic flux spectra are reconstructed. These are used to calculate various photodissociation rates.
Analysis of a summer smog episode in the Berlin-Brandenburg region with a nested atmosphere – chemistry model
Authors: Bauer S. E. , Langmann B.
Published: April 2010

Abstract. An analysis of a pollution episode in an urban atmosphere, using a complex model system is presented. The nested atmosphere-chemistry model system simulates the atmospheric conditions during a one week measurement campaign, called FLUMOB, in July 1994 in Berlin-Brandenburg, Germany. The analysis shows that naturally emitted hydrocarbons played the dominant role in the ozone formation in the investigated area. The composition of non-methane volatile organic compounds was made up to 70--80% by biogenically emitted hydrocarbons. During the analysed case, ozone formation was sensitive to hydrocarbon concentrations so that the ozone production was limited by the availability of hydrocarbons and thus especially by the amount which was biogenically emitted. Furthermore, it is shown that the FLUMOB episode was influenced by elevated concentrations of ozone in the free troposphere. In contrast to previous analyses, the importance of ozone produced outside of Europe is emphasized. In spite of the stagnant high pressure situation which occurred during the FLUMOB episode Germany was significantly influenced by long-range transport of ozone. This transport also influenced near surface ozone concentrations.
Modelling transport and deposition of caesium and iodine from the Chernobyl accident using the DREAM model
Authors: Brandt J. , Christensen J. H. , Frohn L. M.
Published: April 2010

Abstract. A tracer model, DREAM (the Danish Rimpuff and Eulerian Accidental release Model), has been developed for modelling transport, dispersion and deposition (wet and dry) of radioactive material from accidental releases, as the Chernobyl accident. The model is a combination of a Lagrangian model, that includes the near source dispersion, and an Eulerian model describing the long-range transport. The performance of the transport model has previously been tested within the European Tracer Experiment, ETEX, which included transport and dispersion of an inert, non-depositing tracer from a controlled release. The focus of this paper is the model performance with respect to the deposition of 137Cs, 134Cs and 131I from the Chernobyl accident, using different relatively simple and comprehensive parameterizations. The performance, compared to measurements, of different combinations of parameterizations of wet and dry deposition schemes has been evaluated, using different statistical tests.
Suppression of chlorine activation on aviation-produced volatile particles
Authors: Meilinger S. K. , Kärcher B. , Peter Th.
Published: April 2010

Abstract. We examine the effect of nm-sized aircraft-induced aqueous sulfuric acid (H2SO4/H2O) particles on atmospheric ozone as a function of temperature. Our calculations are based on a previously derived parameterization for the regional-scale perturbations of the sulfate surface area density due to air traffic in the North Atlantic Flight Corridor (NAFC) and a chemical box model. We confirm large scale model results that at temperatures T > 210 K additional ozone loss -- mainly caused by hydrolysis of BrONO2 and N2O5 -- scales in proportion with the aviation-produced increase of the background aerosol surface area. However, at lower temperatures (< 210 K) we isolate two effects which efficiently reduce the aircraft-induced perturbation: (1) background particles growth due to H2O and HNO3 uptake enhance scavenging losses of aviation-produced liquid particles and (2) the Kelvin effect efficiently limits chlorine activation on the small aircraft-induced droplets by reducing the solubility of chemically reacting species. These two effects lead to a substantial reduction of heterogeneous chemistry on aircraft-induced volatile aerosols under cold conditions. In contrast we find contrail ice particles to be potentially important for heterogeneous chlorine activation and ozone depletion. These features have not been taken into consideration in previous global studies of the atmospheric impact of aviation. Therefore, to parameterize them in global chemistry and transport models, we propose the following parameterisation: scale the hydrolysis reactions by the aircraft-induced surface area increase, and neglect heterogeneous chlorine reactions on liquid plume particles but not on ice contrails and aircraft induced ice clouds.
Virtual disjunct eddy covariance measurements of organic compound fluxes from a subalpine forest using proton transfer reaction mass spectrometry
Authors: Karl T. G. , Spirig C. , Prevost P. , Stroud C. , Rinne J. , Greenberg J. , Fall R. , Guenther A.
Published: April 2010

Abstract. A `virtual' disjunct eddy covariance (vDEC) device was tested with field measurements of biogenic VOC fluxes at a subalpine forest site in the Rocky Mountains of the U.S.A. A PTR-MS instrument was used as the VOC sensor. Daily peak emission fluxes of 2-methyl-3-buten-2-ol (MBO), methanol, acetone and acetaldehyde were around 1.5, 1, 0.8 and 0.4 mg m-2 h-1, respectively. High pass filtering due to long sampling lines was investigated in laboratory experiments, and suggested that VOC losses in PTFA lines are generally governed by diffusion laws. Memory effects and surface reactions did not seem to play a dominant role. Model estimates of MBO fluxes compared well with measured fluxes. The results also suggest that latent heat and sensible heat fluxes are reasonably well correlated with VOC fluxes and could be used to predict variations in VOC emissions. The release of MBO, methanol, acetone and acetaldehyde resulted in significant change of tropospheric oxidant levels and a 10--40% increase in ozone levels, as inferred from a photochemical box model. We conclude that vDEC with a PTR-MS instrument is a versatile tool for simultaneous field analysis of multiple VOC fluxes.
Forecast, observation and modelling of a deep stratospheric intrusion event over Europe
Authors: P. Zanis  , T. Trickl  , A. Stohl  , H. Wernli  , O. Cooper  , C. Zerefos  , H. Gaeggeler  , C. Schnabel  , L. Tobler  , P. W. Kubik  , A. Priller  , H. E. Scheel  , H. J. Kanter  , P. Cristofanelli  , C. Forster  , P. James  , E. Gerasopoulos  , A. Delcloo  , A. Papayannis  , H. Claude
Published: April 2010

Abstract. A wide range of measurements was carried out in central and southeastern Europe within the framework of the EU-project STACCATO (Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity) with the principle goal to create a comprehensive data set on stratospheric air intrusions into the troposphere along a rather frequently observed pathway over central Europe from the North Sea to the Mediterranean Sea. The measurements were based on predictions by suitable quasi-operational trajectory calculations using ECMWF forecast data. A predicted deep Stratosphere to Troposphere Transport (STT) event, encountered during the STACCATO period on 20–21 June 2001, could be followed by the measurements network almost from its inception. Observations provide evidence that the intrusion affected large parts of central and southeastern Europe. Especially, the ozone lidar observations on 20–21 June 2001 at Garmisch-Partenkirchen, Germany captured the evolution of two marked tongues of high ozone with the first one reaching almost a height of 2 km, thus providing an excellent data set for model intercomparisons and validation. In addition, for the first time to our knowledge concurrent measurements of the cosmogenic radionuclides 10Be and 7Be and their ratio 10Be/7Be are presented together as stratospheric tracers in a case study of a stratospheric intrusion. The ozone tracer columns calculated with the FLEXPART model were found to be in good agreement with water vapour satellite images, capturing the evolution of the observed dry streamers of stratospheric origin. Furthermore, the time-height cross section of ozone tracer simulated with FLEXPART over Garmisch-Partenkirchen captures with many details the evolution of the two observed high-ozone filaments measured with the IFU lidar, thus demonstrating the considerable progress in model simulations. Finally, the modelled ozone (operationally available since October 1999) from the ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric model is shown to be in very good agreement with the observations during this case study, which provides the first successful validation of a chemical tracer that is used operationally in a weather forecast model. This suggests that coupling chemistry and weather forecast models may significantly improve both weather and chemical forecasts in the future.
An evolution strategy to estimate emission source distributions on a regional scale from atmospheric observations
Authors: O’Brien P. , Corcoran D. , Lowry D.
Published: April 2010

Abstract. In this paper we present an Evolution Strategy (ES) approach towards the estimation of the location and strength of surface emissions of trace gases based on atmospheric concentration measurements and back-trajectory analyses. The details of the ES developed are outlined. The ES is tested using artificial emission maps at different grid resolutions and the results compared to those obtained on the same problems using Singular Value Decomposition (SVD). In almost all cases, the ES improves on SVD at equivalent resolutions. In addition, a number of insights, which the ES approach brings to the problem of source location and emission strength, are discussed, particularly the limitations on the use of measurement and meteorological data in the determination of emission source distribution.
Physical properties and concentration of aerosol particles over the Amazon tropical forest during background and biomass burning conditions
Authors: Guyon P. , Graham B. , Beck J. , Boucher O. , Gerasopoulos E. , Mayol-Bracero O. L. , Roberts G. C. , Artaxo P. , Andreae M. O.
Published: April 2010

Abstract. We investigated the size distribution, scattering and absorption properties of Amazonian aerosols and the optical thickness of the aerosol layer under the pristine background conditions typical of the wet season, as well as during the biomass-burning-influenced dry season. The measurements were made during two campaigns in 1999 as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). In moving from the wet to the dry season, median particle numbers were observed to increase from values comparable to those of the remote marine boundary layer (~400cm−3) to values more commonly associated with urban smog (~4000 cm−3), due to a massive injection of submicron smoke particles. Aerosol optical depths at 500\\,nm increased from 0.05 to 0.8 on average, reaching a value of 2 during the dry season. Scattering and absorption coefficients, measured at 550 nm, showed a concomitant increase from average values of 6.8 and 0.4 Mm−1 to values of 91 and 10 Mm−1, respectively, corresponding to an estimated decrease in single-scattering albedo from ca. 0.97 to 0.91. The roughly tenfold increase in many of the measured parameters attests to the dramatic effect that extensive seasonal biomass burning (deforestation, pasture cleaning) is having on the composition and properties of aerosols over Amazonia. The potential exists for these changes to impact on regional and global climate through changes to the extinction of solar radiation as well as the alteration of cloud properties.