bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the effect of different type of aerosols on UV-B radiation from measurements during EARLINET
Authors: Balis D. S. , Amiridis V. , Zerefos C. , Kazantzidis A. , Kazadzis S. , Bais A. F. , Meleti C. , Papayannis A. , Matthias V. , Dier H.
Published: April 2010

Abstract. Routine lidar measurements of the vertical distribution of the aerosol extinction coefficient and the extinction-to-backscatter ratio have been performed at Thessaloniki, Greece using a Raman lidar system in the frame of the EARLINET project since 2000. Spectral and broadband UV-B irradiance measurements, as well as total ozone observations, were available whenever lidar measurements were obtained. From the available measurements several cases could be identified that allowed the study of the effect of different types of aerosol on the levels of the UV-B solar irradiance at the Earth's surface. The TUV radiative transfer model has been used to simulate the irradiance measurements, using total ozone and the lidar aerosol data as input. From the comparison of the model results with the measured spectra the effective single scattering albedo was determined using an iterative procedure, which has been verified against results from the 1998 Lindenberg Aerosol Characterization Experiment. It is shown that the same aerosol optical depth and same total ozone values can show differences up to 10% in the UV-B irradiance at the Earth's surface, which can be attributed to differences in the aerosol type. It is shown that the combined use of the estimated single scattering albedo and the measured extinction-to-backscatter ratio leads to a better characterization of the aerosol type probed.
Contribution of gaseous and particulate species to droplet solute composition
Authors: Sellegri K. , Laj P. , Marinoni A. , Dupuy R. , Legrand M. , Preunkert S
Published: April 2010

Abstract. Chemical reactions of dissolved gases in the liquid phase play a key role in atmospheric processes both in the formation of secondary atmospheric compounds and their wet removal rate but also in the regulation of the oxidizing capacity of the troposphere (Lelieveld and Crutzen, 1991). The behaviour of gaseous species and their chemical transformation in clouds are difficult to observe experimentally given the complex nature of clouds. In this study, we have deployed an experimental set-up to provide an in-situ quantification of phase partitioning and chemical transformation of both organic (CH3COOH, HCOOH, H2C2O4) and inorganic (NH3, HNO3, SO2, HCl) species in clouds. We found that, carboxylic acids, nitrate, and chloride can be considered close to Henry's law equilibrium, within analytical uncertainty and instrumental errors. On another hand, for reduced nitrogen species, dissolution of material from the gas phase is kinetically limited and never reaches the equilibrium predicted by thermodynamics, resulting in significant sub-saturation of the liquid phase. On the contrary, sulfate is supersaturated in the liquid phase, indicating the presence of significant aerosol-derived material transferred through nucleation scavenging. Upon droplet evaporation, most species, including SO2, tend to efficiently return back into the gas phase. In that sense, these species contribute to acidification (for carboxylic acids) or neutralization (for NH3) of the liquid-phase but not totally of the processed aerosols. The only species that appears to be modified in the multiphase system is nitrate. A fraction of at least 10 to 40% of the liquid phase NO3 originates from dissolved HNO3 of which only a fraction evaporates back to the gas phase upon evaporation, resulting in an NO3 enrichment of the aerosol phase. In-cloud gas-to-particle transfer of HNO3 possibly plays a key role in aerosol acidification and in the modification of their hygroscopic properties. Our study emphasizes the need to account for the in-cloud interaction between particles and gases to provide an adequate modeling of multiphase chemistry systems and its impact on the atmospheric aerosol and gas phases.
Ten-year global distribution of downwelling longwave radiation
Authors: Pavlakis K. G. , Hatzidimitriou D. , Matsoukas C. , Drakakis E. , Hatzianastassiou N. , Vardavas I.
Published: April 2010

Abstract. Downwelling longwave fluxes, DLFs, have been derived for each month over a ten year period (1984–1993), on a global scale with a resolution of 2.5° × 2.5°. The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles. The cloud climatologies were taken from the latest released and improved International Satellite Climatology Project D2 series. Specific humidity and temperature vertical profiles were taken from three different reanalysis datasets; NCEP/NCAR, GEOS, and ECMWF (acronyms explained in main text). DLFs were computed for each reanalysis dataset, with differences reaching values as high as 30 Wm−2 in specific regions, particularly over high altitude areas and deserts. However, globally, the agreement is good, with the rms of the difference between the DLFs derived from the different reanalysis datasets ranging from 5 to 7 Wm−2. The results are presented as geographical distributions and as time series of hemispheric and global averages. The DLF time series based on the different reanalysis datasets show similar seasonal and inter-annual variations, and similar anomalies related to the 86/87 El Niño and 89/90 La Niña events. The global ten-year average of the DLF was found to be between 342.2 Wm−2 and 344.3 Wm−2, depending on the dataset. We also conducted a detailed sensitivity analysis of the calculated DLFs to the key input data. Plots are given that can be used to obtain a quick assessment of the sensitivity of the DLF to each of the three key climatic quantities, for specific climatic conditions corresponding to different regions of the globe. Our model downwelling fluxes are validated against available data from ground-based stations distributed over the globe, as given by the Baseline Surface Radiation Network. There is a negative bias of the model fluxes when compared against BSRN fluxes, ranging from −7 to −9 Wm−2, mostly caused by low cloud amount differences between the station and satellite measurements, particularly in cold climates. Finally, we compare our model results with those of other deterministic models and general circulation models.
First observations of noctilucent clouds by lidar at Svalbard
Authors: Höffner J. , Fricke-Begemann C. , Lübken F.-J.
Published: April 2010

Abstract. In summer 2001 a potassium lidar was installed near Longyearbyen (78° N) on the north polar island of Spitsbergen which is part of the archipelago Svalbard. At the same place a series of meteorological rockets ("falling spheres", FS) were launched which gave temperatures from the lower thermosphere to the stratosphere. The potassium lidar is capable of detecting noctilucent clouds (NLCs) and of measuring temperatures in the lower thermosphere, both under daylight conditions. In this paper we give an overview on the NLC measurements (the first at this latitude) and compare the results with temperatures from meteorological rockets which have been published recently (Lübken and Müllemann, 2003).. NLCs were observed from 12 June (the first day of operation) until 12 August when a period of bad weather started. When the lidar was switched on again on 26 August, no NLC was observed. The mean occurrence frequency in the period 12 June–12 August ("lidar NLC period") is 77%. The mean of all individual NLC peak altitudes is 83.6 km (variability: 1.1 km). The mean peak NLC altitude does not show a significant variation with season. The average top and bottom altitude of the NLC layer is 85.1 and 82.5 km, respectively, with a variability of ~1.2 km. The mean of the maximum volume backscatter coefficient ßmax at our wavelength of 770 nm is 3.9×10−10/m/sr with a large variability of +/−3.8×10−10/m/sr. Comparison of NLC characteristics with measurements at ALOMAR (69° N) shows that the peak altitude and the maximum volume backscatter coefficient are similar at both locations but NLCs occur more frequently at higher latitudes. Simultaneous temperature and NLC measurements are available for 3 flights and show that the NLC layer occurs in the lower part of the height range with super-saturation. The NLC peak occurs over a large range of degree of saturation (S) whereas most models predict the peak at S=1. This demonstrates that steady-state considerations may not be applicable when relating individual NLC properties to background conditions. On the other hand, the mean variation of the NLC appearance with height and season is in agreement with the climatological variation of super-saturation derived from the FS temperature measurements.
MAX-DOAS measurements of atmospheric trace gases in Ny-Ålesund
Authors: Wittrock F. , Oetjen H. , Richter A. , Fietkau S. , Medeke T. , Rozanov A. , Burrows J. P.
Published: April 2010

Abstract. A new approach to derive tropospheric concentrations of some atmospheric trace gases from ground-based UV/vis measurements is described. The instrument, referred to as the MAX-DOAS, is based on the well-known UV/vis instruments, which use the sunlight scattered in the zenith sky as the light source and the method of Differential Optical Absorption Spectroscopy (DOAS) to derive column amounts of absorbers like ozone and nitrogen dioxide. Substantial enhancements have been applied to this standard setup to use different lines of sight near to the horizon as additional light sources (MAX – multi axis). Results from measurements at Ny-Ålesund (79° N, 12° E) are presented and interpreted with the full-spherical radiation transport model SCIATRAN. In particular, measurements of the oxygen dimer O4 which has a known column and vertical distribution in the atmosphere are used to evaluate the sensitivity of the retrieval to parameters such as multiple scattering, solar azimuth, surface albedo and refraction in the atmosphere and also to validate the radiative transport model. As a first application, measurements of NO2 emissions from a ship lying in Ny-Ålesund harbour are presented. The results of this study demonstrate the feasibility of long term UV/vis multi axis measurement that can be used to derive not only column amounts of different trace gases but also some information on the vertical location of these absorbers.
An investigation of ozone and planetary boundary layer dynamics over the complex topography of Grenoble combining measurements and modeling
Authors: Couach O. , Balin I , Jiménez R. , Ristori P. , Perego S. , Kirchner F. , Simeonov V. , Calpini B. , van den Bergh H.
Published: April 2010

Abstract. This paper concerns an evaluation of ozone (O3) and planetary boundary layer (PBL) dynamics over the complex topography of the Grenoble region through a combination of measurements and mesoscale model (METPHOMOD) predictions for three days, during July 1999. The measurements of O3 and PBL structure were obtained with a Differential Absorption Lidar (DIAL) system, situated 20 km south of Grenoble at Vif (310 m a.s.l.). The combined lidar observations and model calculations are in good agreement with atmospheric measurements obtained with an instrumented aircraft (METAIR). Ozone fluxes were calculated using lidar measurements of ozone vertical profiles concentrations and the horizontal wind speeds measured with a Radar Doppler wind profiler (DEGREANE). The ozone flux patterns indicate that the diurnal cycle of ozone production is controlled by local thermal winds. The convective PBL maximum height was some 2700 m above the land surface while the nighttime residual ozone layer was generally found between 1200 and 2200 m. Finally we evaluate the magnitude of the ozone processes at different altitudes in order to estimate the photochemical ozone production due to the primary pollutants emissions of Grenoble city and the regional network of automobile traffic.
Formation of large NAT particles and denitrification in polar stratosphere: possible role of cosmic rays and effect of solar activity
Authors: Yu F.
Published: April 2010

Abstract. The formation of large nitric acid trihydrate (NAT) particles has important implications for denitrification and ozone depletion. Existing theories can't explain the recent observations of large NAT particles over wide Arctic regions at temperature above ice frost point. Our analyses reveal that high-energy comic rays may induce the freezing of supercooled HNO3−H2O–H2SO4 droplets when they penetrate these thermodynamically unstable droplets. The cosmic ray-induced freezing (CRIF) is consistent with the observed highly selective formation of NAT particles. We suggest that the physics behind the CRIF mechanism is the reorientation of polar solution molecules into the crystalline configuration in the strong electrical fields of moving secondary ions generated by passing cosmic rays. Our simulations indicate that strong solar proton events (SPEs) may significantly enhance the formation of large NAT particles and denitrification. The CRIF mechanism can explain the high correlations between the thin nitrate-rich layers in polar ice cores and major SPEs. The observed enhancement in aerosol backscattering ratio at PSC layers shortly after an SPE and the significant precipitation velocity of the enhanced PSC payers also provide strong support for the CRIF mechanism.
The velocity of meteoroids
Authors: Williams I. P.
Published: April 2010

Abstract. Determining the velocity of meteoroids as they enter the Earth’s atmosphere is very important since the value is fundamental in calculating the orbit of the meteoroid and hence eventually its origin. We describe early attempts at this determination and high-light problems that exist today.
Uptake study of ClONO2 and BrONO2 by water droplets
Authors: Deiber G. , George Ch. , Le Calvé S. , Schweitzer F. , Mirabel Ph.
Published: April 2010

Abstract. The uptake kinetics of gaseous ClONO2 and BrONO2 on aqueous surfaces were measured, using the droplet train technique coupled to a mass spectrometer, as a function of temperature and liquid composition (pure water and NaCl or NaBr containing solutions). The uptake kinetics are driven by the reactivity of these gases and, for both compounds, the uptake rates on pure water or on NaCl solutions (0.1 M) are comparable. The uptake coefficient γ of ClONO2 does not depend on the temperature while that of BrONO2 increases slightly when the temperature is raised from 272 to 280 K. For ClONO2 and BrONO2, the uptake rates increase on NaBr-doped droplets, enabling the estimation of the mass accommodation coefficient α. The corresponding values for α are 0.108±0.001 for ClONO2 and 0.063±0.009 for BrONO2. The reactions of ClONO2 and BrONO2 on NaCl solutions lead, respectively to the formation of Cl2 and BrCl. The uptake of ClONO2 on NaBr solutions generates BrCl as primary product, which in turn can react with NaBr to produce Br2. As expected, the only product of BrONO2 reaction on NaBr solution is Br2.
Radar and optical leonids
Authors: Brosch N. , Polishook D. , Helled R. , Schijvarg S. , Rosenkrantz M.
Published: April 2010

Abstract. We present joint optical-radar observations of meteors collected near the peak of the leonid activity in 2002. We show four examples of joint detections with a large, phased array L-band radar and with intensified video cameras. The general characteristic of the radar-detected optical meteors is that they show the radar detection below the termination of the optical meteor. Therefore, at least some radar events associated with meteor activity are neither head echoes nor trail echoes, but probably indicate the formation of "charged clouds" after the visual meteor is extinguished.
Gas-particle interactions above a Dutch heathland: I. Surface exchange fluxes of NH3, SO2, HNO3 and HCl
Authors: Nemitz E. , Sutton M. A. , Wyers G. P. , Jongejan P. A. C.
Published: April 2010

Abstract. A field measurement campaign was carried out over a Dutch heathland to investigate the effect of gas-to-particle conversion and ammonium aerosol evaporation on surface/atmosphere fluxes of ammonia and related species. Continuous micrometeorological measurements of the surface exchange of NH3, SO2, HNO3 and HCl were made and are analyzed here with regard to average fluxes, deposition velocities (Vd), canopy resistances (Rc) and canopy compensation point for NH3. Gradients of SO2, HNO3 and HCl were measured with a novel wet-denuder system with online anion chromatography. Measurements of HNO3 and HCl indicate an Rc of 100 to 200 s m−1 during warm daytime periods, probably at least partly due to non-zero acid partial pressures above NH4NO3 and NH4Cl on the leaf surfaces. Although it is likely that this observation is exacerbated by the effect of the evaporation of airborne NH4+ on the gradient measurements, the findings nevertheless add to the growing evidence that HNO3 and HCl are not always deposited at the maximum rate. Ammonia (NH3) fluxes show mainly deposition, with some periods of significant daytime emission. The net exchange could be reproduced both with an Rc model (deposition fluxes only) using resistance parameterizations from former measurements, as well as with the canopy compensation point model, using parameterizations derived from the measurements. The apoplastic ratio of ammonium and hydrogen concentration (Γs=[NH4+]/[H+]) of 1200 estimated from the measurements is large for semi- natural vegetation, but smaller than indicated by previous measurements at this site.
Gas-particle interactions above a Dutch heathland: III. Modelling the influence of the NH3-HNO3-NH4NO3 equilibrium on size-segregated particle fluxes
Authors: Nemitz E. , Sutton M. A.
Published: April 2010

Abstract. Micrometeorological measurements of size-segregated particle number fluxes above Dutch heathlands and forests have repeatedly shown simultaneous apparent emission of particles with a diameter (Dp) < 0.18 µm and deposition of larger particles when measured with optical particle counters. In order to assess whether this observation may be explained by the equilibrium reaction of ammonia (NH3), nitric acid (HNO3) and ammonium (NH4+), a new numerical model is developed to predict the vertical concentration and flux profiles of the different species as modified by the interaction of equilibration and surface/atmosphere exchange processes. In addition to former studies, the new approach explicitly models the height-dependence of the NH4+ and total aerosol size-distribution. Using this model, it is demonstrated that both gas-to-particle conversion (gtpc) and aerosol evaporation can significantly alter the apparent surface exchange fluxes, and evoke the observed bi-directional particle fluxes under certain conditions. Thus, in general, the NH3-HNO3-NH4NO3 equilibrium needs to be considered when interpreting eddy-covariance particle fluxes. Applied to an extensive dataset of simultaneous flux measurements of particles and gases at Elspeet, NL, the model reproduces the diurnal pattern of the bi-directional exchange well. In agreement with the observation of fast NH4+ deposition, slow nitric acid deposition (both as measured by the aerodynamic gradient method) and small concentration products of NH3×HNO3 at this site, this study suggests that NH4+ evaporation at this site significantly alters surface exchange fluxes.
Highly resolved global distribution of tropospheric NO2 using GOME narrow swath mode data
Authors: Beirle S. , Platt U. , Wenig M. , Wagner T.
Published: April 2010

Abstract. The Global Ozone Monitoring Experiment (GOME, since 1995) allows the retrieval of global total column densities of atmospheric trace gases, including NO2. Tropospheric vertical column densities (VCDs) are derived by estimating the stratospheric fraction from measurements over the remote ocean. Mean maps of tropospheric NO2 VCDs derived from GOME clearly allow to detect regions with enhanced industrial activity, but the standard spatial resolution of the GOME ground pixels (320×40 km2) is insufficient to resolve regional trace gas distributions or individual cities. Within the nominal GOME operation, every tenth day measurements in the so called narrow swath mode are executed with a much better spatial resolution (80×40 km2). Though the global coverage of these data is – due to the narrow swath – rather poor, the mean distribution over several years (1997–2001) allows to construct a much more detailed picture of the global NO2 distribution, especially if corrected for seasonal effects. It vividly illustrates the shortcomings of the standard size GOME pixels and reveals an unprecedented wealth of details in the global distribution of tropospheric NO2. Sharply localised spots of enhanced NO2 VCD can be associated directly to cities, large power plants, and heavy industry centers. The long time series of GOME data allows a quantitative comparison of the narrow swath mode data to the nominal resolution that holds general information on the dependency of NO2 VCDs on pixel size. This is important for new instruments like SCIAMACHY (launched March 2002 on ENVISAT) or OMI and GOME II (to be launched 2004 and 2005, respectively) with an improved spatial resolution.
Influence of stratospheric airmasses on tropospheric vertical O3 columns based on GOME (Global Ozone Monitoring Experiment) measurements and backtrajectory calculation over the Pacific
Authors: Ladstätter-Weißenmayer A. , Meyer-Arnek J. , Schlemm A. , Burrows J. P.
Published: April 2010

Abstract. Satellite based GOME (Global Ozone Measuring experiment) data are used to characterize the amount of tropospheric ozone over the tropical Pacific. Tropospheric ozone was determined from GOME data using the Tropospheric Excess Method (TEM). In the tropical Pacific a significant seasonal variation is detected. Tropospheric excess ozone is enhanced during the biomass burning season from September to November due to outflow from the continents. In September 1999 GOME data reveal an episode of increased excess ozone columns over Tahiti (18.0° S; 149.0° W) (Eastern Pacific) compared to Am. Samoa (14.23° S; 170.56° W) and Fiji (18.13° S; 178.40° E), both situated in the Western Pacific. Backtrajectory calculations show that none of the airmasses arriving over the three locations experienced anthropogenic pollution (e.g. biomass burning). Consequently other sources of ozone have to be considered. One possible process leading to an increase of tropospheric ozone is stratosphere-troposphere-exchange. An analysis of the potential vorticity along trajectories arriving above each of the locations reveals that airmasses at Tahiti are subject to enhanced stratospheric influence, compared to Am. Samoa and Fiji. As a result this study shows clear incidents of transport of airmasses from the stratosphere into the troposphere.
Model calculations of the age of firn air across the Antarctic continent
Authors: Kaspers K. A. , van de Wal R. S. W. , van de Broeke M. R. , Schwander J. , van Lipzig N. P. M. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. The age of firn air in Antarctica at pore close-off depth is only known for a few specific sites where firn air has been sampled for analyses. We present a model that calculates the age of firn air at pore close-off depth for the entire Antarctic continent. The model basically uses four meteorological parameters as input (surface temperature, pressure, accumulation rate and wind speed). Using parameterisations for surface snow density, pore close-off density and tortuosity, in combination with a density-depth model and data of a regional atmospheric climate model, distribution of pore close-off depth for the entire Antarctic continent is determined. The deepest pore close-off depth was found for the East Antarctic Plateau near 72° E, 82° S, at 150±15 m (2σ). A firn air diffusion model was applied to calculate the age of CO2 at pore close-off depth. The results predict that the oldest firn gas (CO2 age) is located between Dome Fuji, Dome Argos and Vostok at 43° E, 78° S being 148±23 (1σ or 38 for 2σ) years old. At this location an atmospheric trace gas record should be obtained. In this study we show that methyl chloride could be recorded with a predicted length of 125 years as an example for trace gas records at this location. The longest record currently available from firn air is derived at South Pole, being 80 years. Sensitivity tests reveal that the locations with old firn air (East Antarctic Plateau) have an estimated uncertainty (2σ) for the modelled CO2 age at pore close-off depth of 30% and of about 40% for locations with younger firn air (CO2 age typically 40 years). Comparing the modelled age of CO2 at pore close-off depth with directly determined ages at seven sites yielded a correlation coefficient of 0.90 and a slope close to 1, suggesting a high level of confidence for the modelled results in spite of considerable remaining uncertainties.
A parameterisation of the soot aging for global climate models
Authors: Riemer N. , Vogel H. , Vogel B.
Published: April 2010

Abstract. The representation of soot in global climate models is desirable since it contributes to both the direct and indirect climate effect. While freshly emitted soot is initially hydrophobic and externally mixed, it can be transferred into an internal mixture by coagulation, condensation or photochemical processes. These aging processes affect the hygroscopic qualities and hence the growth behaviour, the optical properties and eventually the lifetime of the soot particles. However, due to computational limits the aging of soot in global climate models is often only parameterised by an estimated turnover rate resulting in a lifetime of soot of several days. Based on the results of our simulations with a comprehensive mesoscale model, we derive the timescale on which diesel soot is transferred from an external to internal mixture, and propose a parameterisation for the use in global climate models. This parameterisation is applicable to continental conditions in industrialised areas as can be found in Central Europe and North America. For daytime conditions, away from the sources, condensation is dominant and the aging process occurs very fast with a timescale of τ=2 h. During night time condensation is not effective. Then coagulation is the most important aging process and our parameterisation leads to a timescale between 10 h and 40 h.
Remote sensing of water cloud droplet size distributions using the backscatter glory: a case study
Authors: Mayer B. , Schröder M. , Preusker R. , Schüller L.
Published: April 2010

Abstract. Cloud single scattering properties are mainly determined by the effective radius of the droplet size distribution. There are only few exceptions where the shape of the size distribution affects the optical properties, in particular the rainbow and the glory directions of the scattering phase function. Using observations by the Compact Airborne Spectrographic Imager (CASI) in 180° backscatter geometry, we found that high angular resolution aircraft observations of the glory provide unique new information which is not available from traditional remote sensing techniques: Using only one single wavelength, 753 nm, we were able to determine not only optical thickness and effective radius, but also the width of the size distribution at cloud top. Applying this novel technique to the ACE-2 CLOUDYCOLUMN experiment, we found that the size distributions were much narrower than usually assumed in radiation calculations which is in agreement with in-situ observations during this campaign. While the shape of the size distribution has only little relevance for the radiative properties of clouds, it is extremely important for understanding their formation and evolution.
Nitrogen oxides measurements in an Amazon site and enhancements associated with a cold front
Authors: Cordova A. M. , Longo K. , Freitas S. , Gatti L. V. , Artaxo P. , Procópio A. , Silva Dias M. A. F. , Freitas E. D.
Published: April 2010

Abstract. An intensive atmospheric chemistry study was carried out in a pristine Amazonian forest site (Balbina), Amazonas state, Brazil during the 2001 wet season, as part of the LBA/CLAIRE 2001 (The Large Scale Biosphere Atmosphere Experiment in Amazonia/Cooperative LBA Airborne Regional Experiment) field campaign. Measurements of nitrogen oxide (NO), nitrogen dioxide (NO2) and ozone (O3) were performed simultaneously with aerosol particles and black carbon concentrations and meteorological parameters observations. Very low trace gases and aerosol concentrations are typically observed at this pristine tropical site. During the measurement period, there was a three-day episode of enhancement of NO2 and black carbon concentration. NO2 concentration reached a maximum value of 4 ppbv, which corresponds to three times the background concentration observed for this site. Black carbon concentration increased from the approximated 100 ng/m3 average value to a 200 ng/m3 maximum during the same period. Biomass burning spots were detected southward, between latitudes 15 to 10° S, 5–6 days before this episode from GOES-8 WF_ABBA (Wildfire Automated Biomass Burning Algorithm). An atmospheric numerical simulation of the whole measurement period was carried out using the RAMS model coupled to a biomass burning emission and transport model. The simulation results pictured a smoke transport event from Central Brazil associated to an approach of a mid-latitude cold front, reinforcing the hypothesis of biomass burning products being long-range transported from the South by the cold front and crossing the Equator. This transport event shows how the pristine atmosphere pattern in Amazonia is impacted by biomass burning emissions from sites very far away.
Noctilucent clouds and the mesospheric water vapour: the past decade
Authors: von Zahn U. , Berger U. , Fiedler J. , Hartogh P.
Published: April 2010

Abstract. The topic of this paper is the expected (from modelling) and observed sensitivity of the brightness β of noctilucent clouds (NLC) on the ambient water vapour mixing ratio f(H2O). Firstly, we show that state-of-the-art models of NLC layer formation predict that in the Arctic summer, a 10% increase of f(H2O) in the upper mesosphere should lead to a 22% increase in β. Secondly, we review observations of episodic changes in f(H2O) and those in β, the former being available since 1992, the latter since 1979. We also add a new series of observations of f(H2O) in the Arctic summer, performed at the ALOMAR observatory (69° N). Thirdly, we show that an increase in daily averaged f(H2O) observed in the Arctic summer since 1996, when introduced into the NLC models, comes close to explaining the observed increase in β. In contrast to this gratifying situation for the summer means of f(H2O) and β (the latter being available only in summer anyway), the behaviour of annual means of f(H2O) is quite different. Those indicate that since 1996 significant decreases of annually averaged upper mesospheric water vapour have occurred at low, mid, and high latitude which can not be used to explain the observed near-stability in NLC brightness over this time period. We close with comments on the very different character of decadal variations in NLC brightness and occurrence rate.
Physical properties of the sub-micrometer aerosol over the Amazon rain forest during the wet-to-dry season transition – comparison of modeled and measured CCN concentrations
Authors: Rissler J. , Swietlicki E. , Zhou J. , Roberts G. , Andreae M. O. , Gatti L. V. , Artaxo P.
Published: April 2010

Abstract. We studied the sub-micrometer atmospheric aerosol particles in the Amazon region, 125 km northeast of Manaus (−1°55.2' S, 59°28.1' W). The measurements were performed during the wet-to-dry transition period, 4–28 July 2001 as part of the LBA (Large-Scale Biosphere Atmosphere Experiment in Amazonia) CLAIRE-2001 (Cooperative LBA Airborne Regional Experiment) experiment. The number size distribution was measured with two parallel differential mobility analyzers, the hygroscopic growth at 90% RH with a hygroscopic tandem mobility analyzer (H-TDMA) and the concentrations of cloud condensation nuclei (CCN) with a cloud condensation nuclei counter (CCNC). We developed a model to predict from H-TDMA data the number of soluble molecules or ions in the particles and the corresponding minimum particle diameter for activation to a cloud droplet at a certain supersaturation. Integrating the number size distribution above this diameter, CCN concentrations were predicted with a time resolution of 10 min and compared to the measured concentrations. During the study period, three different air masses were classified and compared: clean background, air influenced by aged biomass burning, and moderately polluted air from fresh local burning. For the clean period 2001, similar number size distributions and hygroscopic behavior were observed as during the wet season at the same site in 1998, with mostly internally mixed particles of low diameter growth factor (Gf~1.3 taken from dry to 90% RH). During the periods influenced by biomass burning the hygroscopic growth changed slightly, but the largest difference was seen in the number size distribution. The CCN model was found to be successful in predicting the measured CCN concentrations, typically within 25%. A sensitivity study showed relatively small dependence on the assumption of which model salt that was used to predict CCN concentrations from H-TDMA data. One strength of using H-TDMA data to predict CCN concentrations is that the model can also take into account the solubility of organic compounds, insofar as they go into solution at 90% RH. Another advantage is the higher time resolution compared to using size-resolved chemical composition data.
Dust altitude and infrared optical depth from AIRS
Authors: Pierangelo C. , Chédin A. , Heilliette S. , Jacquinet-Husson N. , Armante R.
Published: April 2010

Abstract. We show that mineral dust optical depth and altitude can be retrieved from the Aqua – Advanced Infrared Radiation Sounder (AIRS) measurements. Sensitivity studies performed with a high spectral resolution radiative transfer code show that dust effect on brightness temperatures may reach about 10 Kelvins for some channels. Using a Look-Up-Table approach, we retrieve not only the 10 µm optical depth but also the altitude of Saharan dust layer, above the Atlantic Ocean, from April to September 2003. A key point of our method relies in its ability to retrieve dust altitude from satellite observations. The time and space distribution of the optical depth is in good agreement with the Moderate resolution Imaging Spectroradiometer (MODIS) products. Comparing MODIS and AIRS aerosol optical depths, we find that the ratio between infrared and visible optical depths decreases during transport from 0.35 to 0.22, revealing a loss in coarse particles caused by gravitational settling. The evolution of dust altitude from spring to summer is in agreement with the transport seasonality.
Mass balance inverse modelling of methane in the 1990s using a Chemistry Transport Model
Authors: Butler T. M. , Simmonds I. , Rayner P. J.
Published: April 2010

Abstract. A mass balance inverse modelling procedure is applied with a time-dependent methane concentration boundary condition and a chemical transport model to relate observed changes in the surface distribution of methane mixing ratios during the 1990s to changes in its surface sources. This work serves as an important starting point for future inverse modelling work examining changes in both the source and sink terms in the methane budget together. The model reproduces essential features of the global methane cycle, such as the latitudinal distribution and seasonal cycle of fluxes, without using a priori knowledge of methane fluxes. A detailed description of the temporal and spatial variability of the fluxes diagnosed by the inverse procedure is presented, and compared with previously hypothesised changes in the methane budget, and previous inverse modelling studies. The sensitivity of the inverse results to the forcing data supplied by surface measurements of methane from the NOAA CMDL cooperative air sampling network is also examined.
Spatial and temporal distribution of atmospheric aerosols in the lowermost troposphere over the Amazonian tropical rainforest
Authors: Krejci R. , Ström J. , de Reus M. , Williams J. , Fischer H. , Andreae M. O. , Hansson H.-C.
Published: April 2010

Abstract. We present measurements of aerosol physico-chemical properties below 5 km altitude over the tropical rain forest and the marine boundary layer (MBL) obtained during the LBA-CLAIRE 1998 project. The MBL aerosol size distribution some 50–100 km of the coast of French Guyana and Suriname showed a bi-modal shape typical of aged and cloud processed aerosol. The average particle number density in the MBL was 383 cm−3. The daytime mixed layer height over the rain forest for undisturbed conditions was estimated to be between 1200–1500 m. During the morning hours the height of the mixed layer increased by 4–5 cm s−1. The median daytime aerosol number density in the mixed layer increased from 450 cm−3 in the morning to almost 800 cm−3 in the late afternoon. The evolution of the aerosol size distribution in the daytime mixed layer over the rain forest showed two distinct patterns. Between dawn and midday, the Aitken mode particle concentrations increased, whereas later during the day, a sharp increase of the accumulation mode aerosol number densities was observed, resulting in a doubling of the morning accumulation mode concentrations from 150 cm−3 to 300 cm−3. Potential sources of the Aitken mode particles are discussed here including the rapid growth of ultrafine aerosol particles formed aloft and subsequently entrained into the mixed layer, as well as the contribution of emissions from the tropical vegetation to Aitken mode number densities. The observed increase of the accumulation mode aerosol number densities is attributed to the combined effect of: the direct emissions of primary biogenic particles from the rain forest and aerosol in-cloud processing by shallow convective clouds. Based on the similarities among the number densities, the size distributions and the composition of the aerosol in the MBL and the nocturnal residual layer we propose that the air originating in the MBL is transported above the nocturnal mixed layer up to 300–400 km inland over the rain forest by night without significant processing.
Systematic lumping of complex tropospheric chemical mechanisms using a time-scale based approach
Authors: Whitehouse L. E. , Tomlin A. S. , Pilling M. J.
Published: April 2010

Abstract. This paper presents a formal method of species lumping that can be applied automatically to intermediate compounds within detailed and complex tropospheric chemical reaction schemes. The method is based on grouping species with reference to their chemical lifetimes and reactivity structures. A method for determining the forward and reverse transformations between individual and lumped compounds is developed. Preliminary application to the Leeds Master Chemical Mechanism (MCMv2.0) has led to the removal of 734 species and 1777 reactions from the scheme, with minimal degradation of accuracy across a wide range of test trajectories relevant to polluted tropospheric conditions. The lumped groups are seen to relate to groups of peroxy acyl nitrates, nitrates, carbonates, oxepins, substituted phenols, oxeacids and peracids with similar lifetimes and reaction rates with OH. In combination with other reduction techniques, such as sensitivity analysis and the application of the quasi-steady state approximation (QSSA), a reduced mechanism has been developed that contains 35% of the number of species and 40% of the number of reactions compared to the full mechanism. This has led to a speed up of a factor of 8 in terms of computer calculation time within box model simulations.
Kinetic nucleation and ions in boreal particle formation events
Authors: Laakso L. , Anttila T. , Lehtinen K. E. J. , Aalto P. P. , Kulmala M. , Hõrrak U. , Paatero J. , Hanke M. , Arnold F.
Published: April 2010

Abstract. In order to gain a more comprehensive picture on different mechanisms behind atmospheric particle formation, measurement results from QUEST 2-campaign are analyzed with an aid of an aerosol dynamic model. A special emphasis is laid on air ion and charged aerosol dynamics. Conducted model simulations indicate that kinetic nucleation of ammonia and sulphuric acid together with condensation of sulphuric acid and low-volatile organic vapours onto clusters and particles explain basic features of particle formation events as well as ion characteristics. However, observed excess of negative ions in the diameter range 1.5–3 nm and overcharge of 3–5 nm particles demonstrate that ions are also involved in particle formation. These observations can be explained by preferential condensation of sulphuric acid onto negatively charged clusters and particles. According to model simulations, the relative contribution of ion-based particle formation seem to be smaller than kinetic nucleation of neutral clusters. Conducted model simulations also corroborate the recently-presented hypothesis according to which a large number of so-called thermodynamically stable clusters (TSCs) having a diameter between 1–3 nm exist in the atmosphere. TSCs were found to grow to the observable sizes only under favorable conditions, e.g. when the pre-existing particle concentration was low.
Evaluation of the vertical diffusion coefficients from ERA-40 with 222Rn simulations
Authors: Olivié D. J. L. , van Velthoven P. F. J. , Beljaars A. C. M.
Published: April 2010

Abstract. Boundary layer turbulence has a profound influence on the distribution of tracers with sources or sinks at the surface. The 40-year ERA-40 meteorological data set of the European Centre for Medium-range Weather Forecasts contains archived vertical diffusion coefficients. We evaluated the use of these archived diffusion coefficients instead of off-line diagnosed coefficients based on other meteorological parameters archived during ERA-40 by investigation of the effect on the distribution of the radioactive tracer 222Rn in the chemistry transport model TM3. In total four different sets of vertical diffusion coefficients are compared: (i) 3-hourly vertical diffusion coefficients archived during the ERA-40 project, (ii) 3-hourly off-line diagnosed coefficients from a non-local scheme based on Holtslag and Boville (1993), Vogelezang and Holtslag (1996), and Beljaars and Viterbo (1999), (iii) 6-hourly coefficients archived during the ERA-40 project, and (iv) 6-hourly off-line diagnosed coefficients based on a local scheme described in Louis (1979) and Louis et al. (1982). The diffusion scheme to diagnose the coefficients off-line in (ii) is similar to the diffusion scheme used during the ERA-40 project (i and iii). The archived diffusion coefficients from the ERA-40 project which are time-averaged cause stronger mixing than the instantaneous off-line diagnosed diffusion coefficients. This can be partially attributed to the effect of instantaneous versus time-averaged coefficients, as well as to differences in the diffusion schemes. The 3-hourly off-line diagnosis of diffusion coefficients can reproduce quite well the 3-hourly archived diffusion coefficients. Boundary layer heights are also available for the sets (ii) and (iii). Both were found to be in reasonable agreement with observations of the boundary layer height from Cabauw in the Netherlands and from the FIFE-campaign in the United States. Simulations of 222Rn with the TM3 model using these four sets of vertical diffusion coefficients are compared to surface measurements of 222Rn in Freiburg, Schauinsland, Cincinnati and Socorro in order to evaluate the effect of these different sets of diffusion coefficients on the tracer transport. It is found that the daily cycle of the 222Rn concentration is well represented using 3-hourly diffusion coefficients. Comparison with observations of 222Rn data with the station in Schauinsland which is situated on a hill shows that all considered schemes underestimate the amplitude of the daily cycle of the 222Rn concentration in the upper part of the atmospheric boundary layer. We conclude that the 3-hourly archived diffusion coefficients from ERA-40 are well suited for use in chemistry transport models.
Stratospheric age of air computed with trajectories based on various 3-D-Var and 4-D-Var data sets
Authors: Scheele M. P. , Siegmund P. C. , van Velthoven P. F. J.
Published: April 2010

Abstract. The age of stratospheric air is computed with a trajectory model, using ECMWF ERA-40 3-D-Var and operational 4-D-Var winds. The sensitivity to the forecast period and assimilation technique are studied, and the results are compared with observations and with results from a chemistry transport model that uses the same data sets. A large number of backward trajectories is started in the stratosphere, and from the fraction of these trajectories that has reached the troposphere, the age of air is computed. A pilot study in the tropical stratosphere shows that the age increases with increasing length of the forecast series. Next, for three selected data sets (3-D-Var 1-day and 4-D-Var 3-day forecast series, and 4-D-Var analyses) 5-year backward trajectories are computed that start all over the globe at an altitude of 20 km. For all data sets the computed ages of air in the extratropics are smaller than observed. For 4-D-Var forecast series they are closest to the observations, but still 0.5–1.5 year too small. Compared to the difference in age between the results for the different data sets, the difference in age between the trajectory and the chemistry transport model results is small.
Past and future simulations of NO2 from a coupled chemistry-climate model in comparison with observations
Authors: Struthers H. , Kreher K. , Austin J. , Schofield R. , Bodeker G. , Johnston P. , Shiona H. , Thomas A.
Published: April 2010

Abstract. Trends in NO2 derived from a 45 year integration of a chemistry-climate model (CCM) run have been compared with ground-based NO2 measurements at Lauder (45° S) and Arrival Heights (78° S). Observed trends in NO2 at both sites exceed the trends in N2O, the primary source gas for stratospheric NO2, suggesting that processes driving the NO2 trend are more complex than direct conversion of N2O to NO2. If CCMs are to accurately estimate future changes in ozone, it is important that they comprehensively include these N2O→NO2 processes since NOx (NO+NO2) concentrations are an important factor affecting ozone concentrations. Comparison of measured and modelled NO2 trends is a sensitive test of the degree to which these processes are incorporated in the CCM used here. At Lauder the 1980–2000 CCM NO2 trends (4.2% per decade at sunrise, 3.9% per decade at sunset) are lower than the observed trends (6.5% per decade at sunrise, 6.0% per decade at sunset) but not significantly different at the 2σ level. Large variability in both the model and measurement data from Arrival Heights makes trend analysis of the data difficult. CCM predictions (2001–2019) of NO2 at Lauder and Arrival Heights show significant reductions in the rate of increase of NO2 compared with the previous 20 years (1980–2000). The model results indicate that the partitioning of oxides of nitrogen changes with time and is influenced by both chemical forcing and circulation changes.