bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of microwave satellite humidity data and radiosonde profiles: A survey of European stations
Authors: John V. O. , Buehler S. A.
Published: April 2010

Abstract. A method to compare upper tropospheric humidity (UTH) from satellite and radiosonde data has been applied to the European radiosonde stations. The method uses microwave data as a benchmark for monitoring the performance of the stations. The present study utilizes three years (2001-2003) of data from channel 18 (183.31±1.00 GHz) of the Advanced Microwave Sounding Unit-B (AMSU-B) aboard the satellites NOAA-15 and NOAA-16. The comparison is done in the radiance space, the radiosonde data were transformed to the channel radiances using a radiative transfer model. The comparison results confirm that there is a dry bias in the UTH measured by the radiosondes. This bias is highly variable among the stations and the years. This variability is attributed mainly to the differences in the radiosonde humidity measurements. The analysis also shows a difference between daytime and nighttime soundings which is attributed to radiation error in the radiosonde data. The dry bias due to this error alone correspond to approximately 11% relative error in the UTH measurements.
Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber
Authors: Bohn B. , Zilken H.
Published: April 2010

Abstract. In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain fractions of 0.74 and 0.67 of external values for photolysis frequencies j(NO2) (NO2+hν→NO+O(3P)) and j(O1D) (O3+hν→O2+O(1D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65-0.86 and 0.60-0.73, for j(NO2) and j(O1D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR.
A simple modeling approach to study the regional impact of a Mediterranean forest isoprene emission on anthropogenic plumes
Authors: Cortinovis J. , Solmon F. , Serça D. , Sarrat C. , Rosset R.
Published: April 2010

Abstract. Research during the past decades has outlined the importance of biogenic isoprene emission in tropospheric chemistry and regional ozone photo-oxidant pollution. The first part of this article focuses on the development and validation of a simple biogenic emission scheme designed for regional studies. Experimental data sets relative to Boreal, Tropical, Temperate and Mediterranean ecosystems are used to estimate the robustness of the scheme at the canopy scale, and over contrasted climatic and ecological conditions. A good agreement is generally found when comparing field measurements and simulated emission fluxes, encouraging us to consider the model suitable for regional application. Limitations of the scheme are nevertheless outlined as well as further on-going improvements. In the second part of the article, the emission scheme is used on line in the broader context of a meso-scale atmospheric chemistry model. Dynamically idealized simulations are carried out to study the chemical interactions of pollutant plumes with realistic isoprene emissions coming from a Mediterranean oak forest. Two types of anthropogenic sources, respectively representative of the Marseille (urban) and Martigues (industrial) French Mediterranean sites, and both characterized by different VOC/NOx are considered. For the Marseille scenario, the impact of biogenic emission on ozone production is larger when the forest is situated in a sub-urban configuration (i.e. downwind distance TOWN-FOREST <30km, considering an advection velocity of 4.2 m.s-1). In this case the enhancement of ozone production due to isoprene can reach +37% in term of maximum surface concentrations and +11% in term of total ozone production. The impact of biogenic emission decreases quite rapidly when the TOWN-FOREST distance increases. For the Martigues scenario, the biogenic impact on the plume is significant up to TOWN-FOREST distance of 90km where the ozone maximum surface concentration enhancement can still reach +30%. For both cases, the importance of the VOC/NOx ratio in the anthropogenic plume and its evolution when interacting with the forest emission are outlined. In complement to real case studies, this idealized approach can be particularly useful for process and sensitivity studies and constitutes a valuable tool to build regional ozone control strategies.
Sources and sinks of acetone, methanol, and acetaldehyde in North Atlantic marine air
Authors: Lewis A. C. , Hopkins J. R. , Carpenter L. J. , Stanton J. , Read K. A. , Pilling M. J.
Published: April 2010

Abstract. Measurements of acetone, methanol, acetaldehyde and a range of non-methane hydrocarbons have been made in North Atlantic marine air at the Mace Head observatory. Under maritime conditions the combination of OVOCs (acetone, methanol and acetaldehyde) contributed up to 85% of the total mass of measured non methane organics in air and up to 80% of the OH radical organic sink, when compared with the sum of all other organic compounds including non-methane hydrocarbons, DMS and OH-reactive halocarbons (trichloromethane and tetrachloroethylene). The observations showed anomalies in the variance and abundance of acetaldehyde and acetone over that expected for species with a remote terrestrial emission source and OH controlled chemical lifetime. A detailed model incorporating an explicit chemical degradation mechanism indicated in situ formation during air mass transport was on timescales longer than the atmospheric lifetime of precursor hydrocarbons or primary emission. The period over which this process was significant was similar to that of airmass motion on intercontinental scales, and formation via this route may reproduce that of a widespread diffuse source. The model indicates that continued short chain OVOC formation occurs many days from the point of emission, via longer lived intermediates of oxidation such as organic peroxides and long chain alcohols.
Spectral actinic flux in the lower troposphere: measurement and 1-D simulations for cloudless, broken cloud and overcast situations
Authors: Kylling A. , Webb A. R. , Kift R. , Gobbi G. P. , Ammannato L. , Barnaba F. , Bais A. , Kazadzis S. , Wendisch M. , Jäkel E. , Schmidt S. , Kniffka A. , Thiel S. , Junkermann W. , Blumthaler M. , Silbernagl R. , Schallhart B. , Schmitt R. , Kjeldstad B. , Thorseth T. M. , Scheirer R. , Mayer B.
Published: April 2010

Abstract. In September 2002, the first INSPECTRO campaign to study the influence of clouds on the spectral actinic flux in the lower troposphere was carried out in East Anglia, England. Measurements of the actinic flux, the irradiance and aerosol and cloud properties were made from four ground stations and by aircraft. The radiation measurements were modelled using the uvspec model and ancillary data. For cloudless conditions, the measurements of the actinic flux were reproduced by 1-D radiative transfer modelling within the measurement and model uncertainties of about ±10%. For overcast days, the ground-based and aircraft radiation measurements and the cloud microphysical property measurements are consistent within the framework of 1-D radiative transfer and within experimental uncertainties. Furthermore, the actinic flux is increased by between 60-100% above the cloud when compared to a cloudless sky, with the largest increase for the optically thickest cloud. Correspondingly, the below cloud actinic flux is decreased by about 55-65%. Just below the cloud top, the downwelling actinic flux has a maximum that is seen in both the measurements and the model results. For broken clouds the traditional cloud fraction approximation is not able to simultaneously reproduce the measured above-cloud enhancement and below-cloud reduction in the actinic flux.
Shipborne solar absorption measurements of CO2, CH4, N2O and CO and comparison with SCIAMACHY WFM-DOAS retrievals
Authors: Warneke T. , de Beek R. , Buchwitz M. , Notholt J. , Schulz A. , Velazco V. , Schrems O.
Published: April 2010

Abstract. CO, CH4, N2O and CO2 were retrieved from high resolution solar absorption spectra obtained during a ship cruise from Capetown to Bremerhaven in January/February 2003 by Fourier Transform Infrared (FTIR) spectroscopy. Precisions of better than 0.5% for the column averaged volume mixing ratios (VMR) of CH4 and CO2 are achieved using of O2 as a reference gas. Shipborne FTIR-measurements of CO and data from SCIAMACHY/ENVISAT retrieved by the Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS) retrieval algorithm show qualitatively the same latitudinal variations. WFM-DOAS data of CH4, N2O and CO2 measured over sea exhibit a great spread. The spread is significantly reduced for satellite measurements over land and a reasonable agreement can be obtained if the shipborne data are compared with the closest SCIAMACHY measurements over land. The number of comparisons is too small to draw conclusions. However, by including only WFM-DOAS data with small errors the shipborne and WFM-DOAS data compare within 5% for CH4 and CO2 and within 30% for N2O.
Intercomparison of O3 profiles observed by SCIAMACHY and ground based microwave instruments
Authors: Palm M. , v. Savigny C. , Warneke T. , Velazco V. , Notholt J. , Künzi K. , Burrows J. , Schrems O.
Published: April 2010

Abstract. Ozone profiles retrieved from limb scattering measurements of the SCIAMACHY instrument based on the satellite ENVISAT are compared to ground-based low altitude resolution remote sensors. All profiles are retrieved using optimal estimation. Following the work of Rodgers and Connor (2003) the retrievals of the ground-based instruments are simulated using the SCIAMACHY retrieval. The SCIAMACHY results and the results of the ground-based microwave radiometer in Bremen and Ny Ålesund agree within the expected covariance of the intercomparison.
Simulating orographic rainfall with a limited-area, non-hydrostatic atmospheric model under idealized forcing
Authors: Pathirana A. , Herath S. , Yamada T.
Published: April 2010

Abstract. A modified version of an operational 3-dimensional, non-hydrostatic, limited-area atmospheric model (MM5) was used to perform high-resolution, idealized simulations of the interaction of an infinitely long single ridge with a steady, lateral large-scale wind field. The effect of different mountain ridge dimensions, wind speeds and patterns and moisture profiles on the quantity and distribution of orographic rainfall was investigated. The simulations demonstrated a number of commonly observed mountain flow features like formation of cap clouds, foehn wall, convective break-out associated with mountain topography, interaction of downslope winds with sea breeze, and different stages of cumulus development. It was found that the rainfall maxima associated with the mountain always occur upstream of the ridge peak. Changing mountain dimensions, wind speeds and patterns and moisture profile had clear effects on amount and pattern of accumulated rainfall. Low wind speeds resulted the maximum accumulated rainfall to occur considerable distance upstream of ridge peak. Reversal of wind directions in upper atmosphere caused rainfall to be largely restricted to the wind-side of the peak. The observed rainfall patterns are explained by the different flow patterns observed in the model output.
Is there a trend in cirrus cloud cover due to aircraft traffic?
Authors: Stordal F. , Myhre G. , Stordal E. J. G. , Rossow W. B. , Lee D. S. , Arlander D. W. , Svendby T.
Published: April 2010

Abstract. Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in cirrus. Still we regard the results to be indicative of an impact of aircraft on cirrus amount. The main emphasis of our study is on the area covered by the METEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic contrasts with a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm-2 (lower limit 0.01, upper limit 0.08 Wm-2) for the radiative forcing due to aircraft induced cirrus. The mean is close to the value given by IPCC (1999) as an upper limit.
Large-scale validation of SCIAMACHY reflectance in the ultraviolet
Authors: van Soest G. , Tilstra L. G. , Stammes P.
Published: April 2010

Abstract. In this paper we present an extensive validation of calibrated SCIAMACHY nadir reflectance in the UV (240-400 nm) by comparison with spectra calculated with a fast radiative transfer model. We use operationally delivered near-real-time level 1 data, processed with standard calibration tools. A total of 9 months of data has been analysed. This is the first reflectance validation study incorporating such a large amount of data. It is shown that this method is a valuable tool for spotting spatial and temporal anomalies. We conclude that SCIAMACHY reflectance data in this wavelength range are stable over the investigated period. In addition, we show an example of an anomaly in the data due to an error in the processing chain that could be detected by our comparison. This validation method could be extremely useful too for validation of other satellite spectrometers, such as OMI and GOME-2.
The Indian summer monsoon rainfall: interplay of coupled dynamics, radiation and cloud microphysics
Authors: Patra P. K. , Behera S. K. , Herman J. R. , Maksyutov S. , Akimoto H. , Yamagata Y.
Published: April 2010

Abstract. The Indian summer monsoon rainfall (ISMR), which has a strong connection to agricultural food production, has been less predictable by conventional models in recent times. Two distinct years 2002 and 2003 with lower and higher July rainfall, respectively, are selected to help understand the natural and anthropogenic influences on ISMR. We show that heating gradients along the meridional monsoon circulation are reduced due to aerosol radiative forcing and the Indian Ocean Dipole in 2002. An increase in the dust and biomass-burning component of the aerosols through the zonal monsoon circulation resulted in reduction of cloud droplet growth in July 2002. These conditions were opposite to those in July 2003 which led to an above average ISMR. In this study, we have utilized NCEP/NCAR reanalyses for meteorological data (e.g. sea-surface temperature, horizontal winds, and precipitable water), NOAA interpolated outgoing long-wave radiation, IITM constructed all-India rainfall amounts, aerosol parameters as observed from the TOMS and MODIS satellites, and ATSR fire count maps. Based on this analysis, we suggest that monsoon rainfall prediction models should include synoptic as well as interannual variability in both atmospheric dynamics and chemical composition.
Characterisation of the photolytic HONO-source in the atmosphere simulation chamber SAPHIR
Authors: Rohrer F. , Bohn B. , Brauers T. , Brüning D. , Johnen F.-J. , Wahner A. , Kleffmann J.
Published: April 2010

Abstract. HONO formation has been proposed as an important OH radical source in simulation chambers for more than two decades. Besides the heterogeneous HONO formation by the dark reaction of NO2 and adsorbed water, a photolytic source has been proposed to explain the elevated reactivity in simulation chamber experiments. However, the mechanism of the photolytic process is not well understood so far. As expected, production of HONO and NOx was also observed inside the new atmospheric simulation chamber SAPHIR under solar irradiation. This photolytic HONO and NOx formation was studied with a sensitive HONO instrument under reproducible controlled conditions at atmospheric concentrations of other trace gases. It is shown that the photolytic HONO source in the SAPHIR chamber is not caused by NO2 reactions and that it is the only direct NOy source under illuminated conditions. In addition, the photolysis of nitrate which was recently postulated for the observed photolytic HONO formation on snow, ground, and glass surfaces, can be excluded in the chamber. A photolytic HONO source at the surface of the chamber is proposed which is strongly dependent on humidity, on light intensity, and on temperature. An empirical function describes these dependencies and reproduces the observed HONO formation rates to within 10%. It is shown that the photolysis of HONO represents the dominant radical source in the SAPHIR chamber for typical tropospheric O3/H2O concentrations. For these conditions, the HONO concentrations inside SAPHIR are similar to recent observations in ambient air.
Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation
Authors: Twohy C. H. , Poellot M. R.
Published: April 2010

Abstract. A counterflow virtual impactor was used to collect residual particles larger than about 0.1 μm diameter from anvil cirrus clouds generated over Florida in the southern United States. A wide variety of particle types were found. About one-third of the nuclei were salts, with varying amounts of crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from −21 to −56°C. More insoluble (crustal and metallic) particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about −35 to −40°C, soluble nuclei outnumbered insoluble nuclei, evidently reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice.
The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength
Authors: Walter K. , Graf H.-F.
Published: April 2010

Abstract. Motivated by the strong evidence that the state of the northern hemisphere vortex in boreal winter influences tropospheric variability, teleconnection patterns over the North Atlantic are defined separately for winter episodes where the zonal wind at 50hPa and 65° N is above or below the critical velocity for vertical propagation of zonal planetary wave 1. We argue that the teleconnection structure in the middle and upper troposphere differs considerably between the two regimes of the polar vortex, while this is not the case at sea level. If the polar vortex is strong, there exists one meridional dipole structure of geopotential height in the upper and middle troposphere, which is situated in the central North Atlantic. If the polar vortex is weak, there exist two such dipoles, one over the western and one over the eastern North Atlantic. Storm tracks (and precipitation related with these) are determined by mid and upper tropospheric conditions and we find significant differences of these parameters between the stratospheric regimes. For the strong polar vortex regime, in case of a negative upper tropospheric "NAO" index we find a blocking height situation over the Northeast Atlantic and the strongest storm track of all. It is reaching far north into the Arctic Ocean and has a secondary maximum over the Denmark Strait. Such storm track is not found in composites based on a classic NAO defined by surface pressure differences between the Icelandic Low and the Azores High. Our results suggest that it is important to include the state of the polar vortex strength in any study of the variability over the North Atlantic.
A 2003 stratospheric aerosol extinction and PSC climatology from GOMOS measurements on Envisat
Authors: Vanhellemont F. , Fussen D. , Bingen C. , Kyrölä E. , Tamminen J. , Sofieva V. , Hassinen S. , Verronen P. , Seppälä A. , Bertaux J. L. , Hauchecorne A. , Dalaudier F. , Fanton d'Andon O. , Barrot G. , Mangin A. , Theodore B. , Guirlet M. , Renard J. B. , Fraisse R. , Snoeij P. , Koopman R. , Saavedra L.
Published: April 2010

Abstract. Stratospheric aerosols play an important role in a number of atmospheric issues such as midlatitude ozone depletion, atmospheric dynamics and the Earth radiative budget. Polar stratospheric clouds on the other hand are a crucial factor in the yearly Arctic and Antarctic ozone depletion. It is therefore important to quantify the stratospheric aerosol/PSC abundance. In orbit since March 2002, the GOMOS instrument onboard the European Envisat satellite has provided a vast aerosol extinction data set. In this paper we present aerosol/PSC zonal median values that were constructed from this data set, together with a discussion of the results.
Validation of ENVISAT/SCIAMACHY columnar methane by solar FTIR spectrometry at the Ground-Truthing Station Zugspitze
Authors: Sussmann R. , Stremme W. , Buchwitz M. , de Beek R.
Published: April 2010

Abstract. Methane total-vertical column retrievals from ground-based solar FTIR measurements at the Permanent Ground-Truthing Station Zugspitze (47.42° N, 10.98° E, 2964m a.s.l.), Germany are used to validate column averaged methane retrieved from ENVISAT/SCIAMACHY spectra by WFM-DOAS (WFMD) version 0.4 and 0.41 for 153 days in 2003. Smoothing errors are estimated to be below 0.10% for FTIR and 0.14% for SCIAMACHY-WFMD retrievals and can be neglected for the assessment of observed bias and day-to-day-scatter. In order to minimize the altitude-difference effect, dry-air column averaged mixing ratios (XCH4) have been utilized. From the FTIR-time series of XCH4 an atmospheric day-to-day variability of 1% was found, and a sinusoidal annual cycle with a ≈1.6% amplitude. To obtain the WFMD bias, a polynomial fitted to the FTIR series was used as a reference. The result is WFMD v0.4/FTIR=1.008±0.019 and WFMD v0.41/FTIR=1.058±0.008. WFMD v0.41 was significantly improved by a time-dependent bias correction. It can still not capture the natural day-to-day variability, i.e., the standard deviation calculated from the daily-mean values is 2.4% using averages within a 2000-km radius, and 2.7% for a 1000-km radius. These numbers are dominated by a residual time-dependent bias in the order of 3%/month. The latter can be reduced, e.g., from 2.4% to 1.6% as shown by an empirical time-dependent bias correction. Standard deviations of the daily means, calculated from the individual measurements of each day, are excluding time-dependent biases, thus showing the potential precision of WFMD daily means, i.e., 0.3% for a 2000-km selection radius, and 0.6% for a 1000-km selection radius. Therefore, the annual cycle as well as possibly the day-to-day variability could be captured under the prerequisite of further advanced time-dependent bias corrections, or the use of other channels, where the icing issue is less prominent.
Inverse modelling of national and European CH4 emissions using the atmospheric zoom model TM5
Authors: Bergamaschi P. , Krol M. , Dentener F. , Vermeulen A. , Meinhardt F. , Graul R. , Ramonet M. , Peters W. , Dlugokencky E. J.
Published: April 2010

Abstract. A synthesis inversion based on the atmospheric zoom model TM5 is used to derive top-down estimates of CH4 emissions from individual European countries for the year 2001. We employ a model zoom over Europe with 1° × 1° resolution that is two-way nested into the global model domain (with resolution of 6° × 4°. This approach ensures consistent boundary conditions for the zoom domain and thus European top-down estimates consistent with global CH4 observations. The TM5 model, driven by ECMWF analyses, simulates synoptic scale events at most European and global sites fairly well, and the use of high-frequency observations allows exploiting the information content of individual synoptic events. A detailed source attribution is presented for a comprehensive set of 56 monitoring sites, assigning the atmospheric signal to the emissions of individual European countries and larger global regions. The available observational data put significant constraints on emissions from different regions. Within Europe, in particular several Western European countries are well constrained. The inversion results suggest up to 50-90% higher anthropogenic CH4 emissions in 2001 for Germany, France and UK compared to reported UNFCCC values (EEA, 2003). A recent revision of the German inventory, however, resulted in an increase of reported CH4 emissions by 68.5% (EEA, 2004), being now in very good agreement with our top-down estimate. The top-down estimate for Finland is distinctly smaller than the a priori estimate, suggesting much smaller CH4 emissions from Finnish wetlands than derived from the bottom-up inventory. The EU-15 totals are relatively close to UNFCCC values (within 4-30%) and appear very robust for different inversion scenarios.
Technical note: The Lagrangian particle dispersion model FLEXPART version 6.2
Authors: Stohl A. , Forster C. , Frank A. , Seibert P. , Wotawa G.
Published: April 2010

Abstract. The Lagrangian particle dispersion model FLEXPART was originally (about 8 years ago) designed for calculating the long-range and mesoscale dispersion of air pollutants from point sources, such as after an accident in a nuclear power plant. In the meantime FLEXPART has evolved into a comprehensive tool for atmospheric transport modeling and analysis. Its application fields were extended from air pollution studies to other topics where atmospheric transport plays a role (e.g., exchange between the stratosphere and troposphere, or the global water cycle). It has evolved into a true community model that is now being used by at least 25 groups from 14 different countries and is seeing both operational and research applications. A user manual has been kept actual over the years and was distributed over an internet page along with the model's source code. In this note we provide a citeable technical description of FLEXPART's latest version (6.2).
Application of several activity coefficient models to water-organic-electrolyte aerosols of atmospheric interest
Authors: Raatikainen T. , Laaksonen A.
Published: April 2010

Abstract. In this work, existing and modified activity coefficient models are examined in order to assess their capabilities to describe the properties of aqueous solution droplets relevant in the atmosphere. Five different water-organic-electrolyte activity coefficient models were first selected from the literature. Only one of these models included organics and electrolytes which are common in atmospheric aerosol particles. In the other models, organic species were solvents such as alcohols, and important atmospheric ions like NH4+ could be missing. The predictions of these models were compared to experimental activity and solubility data in aqueous single electrolyte solutions with 31 different electrolytes. Based on the deviations from experimental data and on the capabilities of the models, four predictive models were selected for fitting of new parameters for binary and ternary solutions of common atmospheric electrolytes and organics. New electrolytes (H+, NH4+, Na+, Cl-, NO3- and SO42-) and organics (dicarboxylic and some hydroxy acids) were added and some modifications were made to the models if it was found useful. All new and most of the existing parameters were fitted to experimental single electrolyte data as well as data for aqueous organics and aqueous organic-electrolyte solutions. Unfortunately, there are very few data available for organic activities in binary solutions and for organic and electrolyte activities in aqueous organic-electrolyte solutions. This reduces model capabilities in predicting solubilities. After the parameters were fitted, deviations from measurement data were calculated for all fitted models, and for different data types. These deviations and the calculated property values were compared with those from other non-electrolyte and organic-electrolyte models found in the literature. Finally, hygroscopic growth factors were calculated for four 100 nm organic-electrolyte particles and these predictions were compared to experimental data and to predictions from other models. All of the newly fitted models show good agreement with experimental water activity data in binary and ternary solutions. One of the models is for activities of non-electrolytes only, but the other three models show quite small deviations from measured electrolyte activities. Because there were not enough experimental data for organic and electrolyte activities, some models show bigger deviation for mutual deliquescence relative humidities of organic-electrolyte particles, but calculated growth factors for liquid droplets are quite close to the experimental data. Even in cases with somewhat bigger deviations, the results can be considered satisfactory, because they were calculated based mainly on the predictive properties of the models.
Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: development of an explicit model based on a self generating approach
Authors: Aumont B. , Szopa S. , Madronich S.
Published: April 2010

Abstract. Organic compounds emitted in the atmosphere are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these organic intermediates is widely acknowledged, there is still a critical lack of information concerning the detailed composition of the highly functionalized secondary organics in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modelling tools that track the identity and reactivity of organic carbon in the various phases down to the ultimate oxidation products, CO and CO2. However, a fully detailed representation of the atmospheric transformations of organic compounds involves a very large number of intermediate species, far in excess of the number that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidation schemes of acyclic hydrocarbons and their oxidation products under tropospheric conditions and (2) the protocol used to select the reaction products and the rate constants. Results are presented using the fully explicit oxidation schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of organic carbon during the oxidation of a given parent compound are presented.
Assessment of the reduction methods used to develop chemical schemes: building of a new chemical scheme for VOC oxidation suited to three-dimensional multiscale HOx-NOx-VOC chemistry simulations
Authors: Szopa S. , Aumont B. , Madronich S.
Published: April 2010

Abstract. The objective of this work was to develop and assess an automatic procedure to generate reduced chemical schemes for the atmospheric photooxidation of volatile organic carbon (VOC) compounds. The procedure is based on (i) the development of a tool for writing the fully explicit schemes for VOC oxidation (see companion paper Aumont et al., 2005), (ii) the application of several commonly used reduction methods to the fully explicit scheme, and (iii) the assessment of resulting errors based on direct comparison between the reduced and full schemes. The reference scheme included seventy emitted VOCs chosen to be representative of both anthropogenic and biogenic emissions, and their atmospheric degradation chemistry required more than two million reactions among 350000 species. Three methods were applied to reduce the size of the reference chemical scheme: (i) use of operators, based on the redundancy of the reaction sequences involved in the VOC oxidation, (ii) grouping of primary species having similar reactivities into surrogate species and (iii) grouping of some secondary products into surrogate species. The number of species in the final reduced scheme is 147, this being small enough for practical inclusion in current three-dimensional models. Comparisons between the fully explicit and reduced schemes, carried out with a box model for several typical tropospheric conditions, showed that the reduced chemical scheme accurately predicts ozone concentrations and some other aspects of oxidant chemistry for both polluted and clean tropospheric conditions.
CCN activation and cloud processing in sectional aerosol models with low size resolution
Authors: Korhonen H. , Kerminen V.-M. , Lehtinen K. E. J. , Kulmala M.
Published: April 2010

Abstract. We investigate the influence of low size resolution, typical to sectional aerosol models in large scale applications, on cloud droplet activation and cloud processing of aerosol particles. A simplified cloud model with five approaches to determine the fraction of activated particles is compared with a detailed reference model under different atmospheric conditions. In general, activation approaches which assume a distribution profile within the critical model size sections predict the cloud droplet concentration most accurately under clean and moderately polluted conditions. In such cases, the deviation from the reference simulations is below 15% except for very low updraft velocities. In highly polluted cases, the concentration of cloud droplets is significantly overestimated due to the inability of the simplified model to account for the kinetic limitations of the droplet growth. Of the profiles examined, taking into account the local shape of the particle size distribution is the most accurate although in most cases the shape of the profile has little relevance. While the low resolution cloud model cannot reproduce the details of the out-of-the-cloud aerosol size distribution, it captures well the amount of sulphate produced in aqueous-phase reactions as well as the distribution of the sulphate between the cloud droplets. Overall, the simplified cloud model with low size resolution performs well for clean and moderately polluted regions that cover most of the Earth's surface and is therefore suitable for large scale models. It can, however, show uncertainties in areas with strong pollution from anthropogenic sources.
Indicators of Antarctic ozone depletion
Authors: Bodeker G. E. , Shiona H. , Eskes H.
Published: April 2010

Abstract. An assimilated data base of total column ozone measurements from satellites has been used to generate a set of indicators describing attributes of the Antarctic ozone hole for the period 1979 to 2003, including (i) daily measures of the area over Antarctica where ozone levels are below 150 DU, below 220 DU, more than 30% below 1979 to 1981 norms, and more than 50% below 1979 to 1981 norms, (ii) the date of disappearance of 150 DU ozone values, 220 DU ozone values, values 30% below 1979 to 1981 norms, and values 50% below 1979 to 1981 norms, for each year, (iii) daily minimum total column ozone values over Antarctica, and (iv) daily values of the ozone mass deficit based on a O3<220 DU threshold. The assimilated data base combines satellite-based ozone measurements from 4 Total Ozone Mapping Spectrometer (TOMS) instruments, 3 different retrievals from the Global Ozone Monitoring Experiment (GOME), and data from 4 Solar Backscatter Ultra-Violet (SBUV) instruments. Comparisons with the global ground-based Dobson spectrophotometer network are used to remove offsets and drifts between the different data sets to produce a global homogeneous data set that combines the advantages of good spatial coverage of satellite data with good long-term stability of ground-based measurements. One potential use of the derived indices is detection of the expected recovery of the Antarctic ozone hole. The suitability of the derived indicators to this task is discussed in the context of their variability and their susceptibility to saturation effects which makes them less responsive to decreasing stratospheric halogen loading. It is also shown that if the corrections required to match recent Earth Probe TOMS measurements to Dobson measurements are not applied, some of the indictors are affected so as to obscure detection of the recovery of the Antarctic ozone hole.
Two decades of OH variability as inferred by an inversion of atmospheric transport and chemistry of methyl chloroform
Authors: Bousquet P. , Hauglustaine D. A. , Peylin P. , Carouge C. , Ciais P.
Published: April 2010

Abstract. We developed an iterative inverse method to infer inter-annual sources and sinks of methyl chloroform (MCF) from atmospheric measurements, on a monthly basis. The methodology is presented and used to estimate two decades of OH variability between 1980 and 2000, using varying meteorology. When OH concentrations are adjusted with loose prior errors and MCF emissions are adjusted within inventory bounds, we show that substantial OH inter-annual variability (8.5±1.0% of the mean) and trend (-0.7%.yr-1) are necessary to match MCF observations. This result is confirmed by a series of sensitivity tests addressing main limitations of previous studies. However, we show that it is also possible to match MCF observations with a 65% reduction of OH year-to-year variations and a 60% reduction of absolute OH trend, but still a consistency of inferred emissions with inventory values at a ±2σ level. On the other hand, the phase of inferred OH variations is a more robust feature of our set of inversions. Overall, MCF inversions can only provide a range of OH variations unless inventory uncertainties are further reduced.
Stratospheric and tropospheric NO2 variability on the diurnal and annual scale: a combined retrieval from ENVISAT/SCIAMACHY and solar FTIR at the Permanent Ground-Truthing Facility Zugspitze/Garmisch
Authors: Sussmann R. , Stremme W. , Burrows J. P. , Richter A. , Seiler W. , Rettinger M.
Published: April 2010

Abstract. Columnar NO2 retrievals from solar FTIR measurements at the Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.), Germany were investigated synergistically with columnar NO2 retrieved from SCIAMACHY data by the University of Bremen scientific algorithm UB1.5 for the time span July 2002-October 2004. A new concept to match FTIR data to the time of satellite overpass makes use of the NO2 daytime increasing rate retrieved from the FTIR data set itself [+1.02(6)E+14 cm-2/h]. This measured increasing rate shows no significant seasonal variation. SCIAMACHY data within a 200-km radius around Zugspitze were considered, and a pollution-clearing scheme was developed to select only pixels corresponding to clean background (free) tropospheric conditions, and exclude local pollution hot spots. The resulting difference between SCIAMACHY and FTIR columns (without correcting for the different sensitivities of the instruments) varies between 0.60-1.24E+15 cm-2 with an average of 0.83E+15 cm-2. A day-to-day scatter of daily means of ≈7-10% could be retrieved in mutual agreement from FTIR and SCIAMACHY. Both data sets are showing sufficient precisions to make this assessment. Analysis of the averaging kernels gives proof that at high-mountain-site FTIR is a highly accurate measure for the pure stratospheric column, while SCIAMACHY shows significant tropospheric sensitivity. Based on this finding, we set up a combined a posteriori FTIR-SCIAMACHY retrieval for tropospheric NO2, based upon the averaging kernels. It yields an annual cycle of the clean background (free) tropospheric column (<10 km) with variations between 0.75-1.54E+15 cm-2, an average of 1.09E+15 cm-2, and an intermediate phase between that of the well known boundary layer and stratospheric annual cycles. The outcome is a concept for an integrated global observing system for tropospheric NO2 that comprises DOAS nadir satellite measurements and a set of latitudinally distributed mountain-site or clean-air FTIR stations.
The uptake of SO2 on Saharan dust: a flow tube study
Authors: Adams J. W. , Rodriguez D. , Cox R. A.
Published: April 2010

Abstract. The uptake of SO2 onto Saharan mineral dust from the Cape Verde Islands was investigated using a coated wall flow tube coupled to a mass spectrometer. The rate of loss of SO2 to the dust coating was measured and uptake coefficients were determined using the measured BET surface area of the sample. The uptake of SO2, with an initial concentration between (2-40)x1010molecule cm-3 (0.62-12 µTorr), was found to be strongly time dependent over the first few hundred seconds of an experiment, with an initial uptake γ0,BET of (6.6±0.8)x10-5 (298 K), declining at longer times. The amount of SO2 adsorbed on the dust samples was measured over a range of SO2 concentrations and mineral dust loadings. The uptake of SO2 was found to be up to 98% irreversible over the timescale of these investigations. Experiments were also performed at 258 K, at a relative humidity of 27% and at 298 K in the presence of ozone. The initial uptake and the amount of SO2 taken up per unit area of BET dust surface was the same within error, irrespective of the conditions used; however the presence of ozone reduced the amount of SO2 released back into the gas-phase per unit area once exposure of the surface ended. Multiple uptakes to the same surface revealed a loss of surface reactivity, which did not return if the samples were exposed to gas-phase water, or left under vacuum overnight. A mechanism which accounts for the observed uptake behaviour is proposed and numerically modelled, allowing quantitative estimates of the rate and amount of SO2 removal in the atmosphere to be estimated. Removal of SO2 by mineral dust is predicted to be significant at high dust loadings.
Mass transfer effects in hygroscopic measurements of aerosol particles
Authors: Chan M. N. , Chan C. K.
Published: April 2010

Abstract. The tandem differential mobility analyzer (TDMA) has been widely utilized to measure the hygroscopicity of laboratory-generated and atmospheric submicrometer particles. An important concern in investigating the hygroscopicity of the particles is if the particles have attained equilibrium state in the measurements. We present a literature survey to investigate the mass transfer effects in hygroscopicity measurements. In most TDMA studies, a residence time in the order of seconds is used for humidification (or dehumidification). NaCl and (NH4)2SO4 particles are usually used to verify the equilibrium measurements during this residence time, which is presumed to be sufficient for other particles. There have been observations that not all types of submicrometer particles, including atmospheric particles, attain their equilibrium sizes within this time scale. We recommend that experimentation with different residence times be conducted and that the residence time should be explicitly stated in future TDMA measurements. Mass transfer effects may also exist in the measurements of other properties related to the water uptake of atmospheric particles such as relative humidity dependent light scattering coefficients and cloud condensation nuclei activity.
A new convective cloud field model based on principles of self-organisation
Authors: Nober F. J. , Graf H. F.
Published: April 2010

Abstract. A new cumulus convection parameterisation is presented in this paper. The parameterisation uses an explicit spectral approach and determines, unlike other convection schemes, for each convection event a new cloud distribution function regarding to the given vertical temperature and humidity profiles. This is done by using a one dimensional cloud model to create a spectrum of different clouds. The interaction between all non convective physical processes in the AGCM and all different clouds is taken into account to calculate a selfconsistent cloud spectrum. The model has been implemented in the ECHAM5 AGCM and tested against a large eddy simulation model. The representation of a shallow cumulus cloud field by the AGCM could be much improved. Diurnal cycle, cloud cover, liquid water path and the vertical structure of the mass flux, determined by the new convection scheme are close to the large eddy simulation, whereas the standard convection scheme failed in simulating this convection episode.
Atmospheric methanol measurement using selective catalytic methanol to formaldehyde conversion
Authors: Solomon S. J. , Custer T. , Schade G. , Soares Dias A. P. , Burrows J.
Published: April 2010

Abstract. A novel atmospheric methanol measurement technique, employing selective gas-phase catalytic conversion of methanol to formaldehyde followed by detection of the formaldehyde product, has been developed and tested. The effects of temperature, gas flow rate, gas composition, reactor-bed length, and reactor-bed composition on the methanol conversion efficiency of a molybdenum-rich, iron-molybdate catalyst [Mo-Fe-O] were studied. Best results were achieved using a 1:4 mixture (w/w) of the catalyst in quartz sand. Optimal methanol to formaldehyde conversion (>95% efficiency) occurred at a catalyst housing temperature of 345°C and an estimated sample-air/catalyst contact time of <0.2 seconds. Potential interferences arising from conversion of methane and a number of common volatile organic compounds (VOC) to formaldehyde were found to be negligible under most atmospheric conditions and catalyst housing temperatures. Using the new technique, atmospheric measurements of methanol were made at the University of Bremen campus from 1 to 15 July 2004. Methanol mixing ratios ranged from 1 to 5 ppb with distinct maxima at night. Formaldehyde mixing ratios, obtained in conjunction with methanol by periodically bypassing the catalytic converter, ranged from 0.2 to 1.6 ppb with maxima during midday. These results suggest that selective, catalytic methanol to formaldehyde conversion, coupled with existing formaldehyde measurement instrumentation, is an inexpensive and effective means for monitoring atmospheric methanol.