bluuebunny/crossref_metadata_2025 huggingface dataset:
Deployment of a ground-based CIMS apparatus for the detection of organic gases in the boreal forest during the QUEST campaign
Authors: Sellegri K. , Umann B. , Hanke M. , Arnold F.
Published: April 2010

Abstract. Measurements of atmospheric volatile organic compounds were performed in the Finnish Boreal forest atmosphere during spring 2003, as part of the project QUEST (Quantification of Aerosol Nucleation in the European Boundary Layer), using a ground-based Chemical Ionization Mass Spectrometer (CIMS) instrument. Based on the study of their hydrate distribution, Methanol, Acetonitrile, Acetaldehyde, Dimethyl Amine (DMA), Ethanol/Formic Acid, Acetone, Trimethyl Amine TMA, Propanol/Acetic Acid, Methyl Vinyl Ketone (MVK) and Metacrolein (MaCR), Monoterpenes, Cis-3-hexenyl Acetate and Monoterpene Oxidation Products (MTOP) are proposed as candidates for masses 33, 41, 44, 45, 46, 58, 59, 60, 70, 136, 142 and 168 amu, respectively. It would be, to our knowledge, the first time DMA, TMA, MTOP and Cis-3-hexenyl Acetate are measured with this method. A compound with mass 68 amu, which could be Isoprene has also been identified. Most compounds show a clear diurnal variation with higher concentrations at night, starting at the onset of the nocturnal inversion and in agreement with independent measurements of CO. Biogenic compounds are highly correlated with each other and the ratio monoterpene/oxidation product shows a typical daily pattern of nighttime maxima. Cis-3-hexenyl Acetate has a diurnal variation similar to the ones of Isoprene and Monoterpenes, and especially close to the diurnal variation of their oxidation products.
Metal layers at high altitudes: A possible connection to meteoroids
Authors: Höffner J. , Friedman J. S.
Published: April 2010

Abstract. In the past, many studies have been carried out to demonstrate the influence of meteoroids on the atmospheric metal layer, observed roughly in the altitude range 80–105 km. Even with the capability of present day resonance lidars to measure metal densities within single meteor trails, it has been difficult to prove any influence of meteors on the average metal layer. In contrast to approaches taken earlier, we discuss here the seasonal characteristics of potassium, calcium, calcium ion, iron and sodium above 110 km altitude where the average nocturnal densities are so low that the existence of a baseline level of metal atoms and ions is often overlooked. By comparing simultaneous and common-volume observations of different metal layers at one location, we demonstrate that despite their different seasonal characteristics at lower altitudes remarkably similar seasonal characteristics are observed at higher altitudes. In addition, for potassium at different latitudes a qualitative agreement is also found. A comparison of metal densities at 113 km altitude with known meteor showers indicates a strong influence of shower meteoroids on the topside of the metal layers. Simultaneous observations of K along with Ca, Fe and/or Na permits the calculation of abundance ratios. We find that these ratios at 113 km altitude are quite similar to values measured in single meteor trails by ground based lidars. Given these evidences, we contend that there is a direct influence of ablating meteoroids on the topside of the mesospheric metal layer. Furthermore, the increase in densities throughout summer with similar abundance ratios as observed during meteor showers is a strong evidence for the influence of sporadic meteoroids on the high metal layers.
Enhanced uptake of water by oxidatively processed oleic acid
Authors: Asad A. , Mmereki B. T. , Donaldson D. J.
Published: April 2010

Abstract. A quartz crystal microbalance apparatus has been used to measure the room temperature uptake of water vapour by thin films of oleic acid as a function of relative humidity, both before and following exposure of the films to various partial pressures of gas phase ozone. A rapid increase in the water-sorbing ability of the film is observed as its exposure to ozone is increased, followed by a plateau region in which no additional water is taken up. In this fully-processed region the mass of water taken up by the film is about 4 times that of the unprocessed film. Infrared spectra of the films, measured after variable exposures to ozone, show dramatic increases in both the "free" and hydrogen-bonded O-H stretching regions, and a decrease in the intensity of olefinic features. These results are consistent with the formation of an oxygenated polymeric product or products, as well as the gas phase products previously identified.
An investigation of processes controlling the evolution of the boundary layer aerosol size distribution properties at the Swedish background station Aspvreten
Authors: Tunved P. , Ström J. , Hansson H.-C.
Published: April 2010

Abstract. Aerosol size distributions have been measured at the Swedish background station Aspvreten (58.8° N, 17.4° E). Different states of the aerosol were determined using a novel application of cluster analysis. The analysis resulted in eight different clusters capturing the different stages of the aerosol lifecycle. The aerosol was interpreted as belonging to fresh, intermediate and aged type of size distribution and different magnitudes thereof. With aid of back trajectory analysis we present statistics concerning the relation of source area and different meteorological parameters using a non-lagrangian approach. Source area is argued to be important although not sufficient to describe the observed aerosol properties. Especially processing by clouds and precipitation is shown to be crucial for the evolution of the aerosol size distribution. As much as 60% of the observed size distributions present features likely related to cloud processes or wet deposition. The lifetime properties of different sized aerosols are discussed by means of measured variability. Processing by non-precipitating clouds most obviously affect aerosols in the size range 100 nm and larger. This indicates an approximate limit for activation in clouds to 100 nm in this type of environment. The aerosol lifecycle is discussed. Size distributions bearing signs of recent new particle formation (~30% of the observed size distributions) represent the first stage in the lifecycle. Aging may proceed in two directions: either growth by condensation and coagulation or processing by non-precipitating clouds. In both cases mass is accumulated. Wet removal is the main process capable of removing aerosol mass. Wet deposition is argued to be an important mechanism in reaching a state where nucleation may occur (i.e. sufficiently low aerosol surface area) in environments similar to the one studied.
Multicomponent aerosol dynamics model UHMA: model development and validation
Authors: Korhonen H. , Lehtinen K. E. J. , Kulmala M.
Published: April 2010

Abstract. A size-segregated aerosol dynamics model UHMA (University of Helsinki Multicomponent Aerosol model) was developed for studies of multicomponent tropospheric aerosol particles. The model includes major aerosol microphysical processes in the atmosphere with a focus on new particle formation and growth; thus it incorporates particle coagulation and multicomponent condensation, applying a revised treatment of condensation flux onto free molecular regime particles and the activation of nanosized clusters by organic vapours (Nano-Köhler theory), as well as recent parameterizations for binary H2SO4–H2O and ternary H2SO4–NH3-H2O homogeneous nucleation and dry deposition. The representation of particle size distribution can be chosen from three sectional methods: the hybrid method, the moving center method, and the retracking method in which moving sections are retracked to a fixed grid after a certain time interval. All these methods can treat particle emissions and transport consistently, and are therefore suitable for use in large scale atmospheric models. In a test simulation against an accurate high resolution solution, all the methods showed reasonable treatment of new particle formation with 20 size sections although the hybrid and the retracking methods suffered from artificial widening of the distribution. The moving center approach, on the other hand, showed extra dents in the particle size distribution and failed to predict the onset of detectable particle formation. In a separate test simulation of an observed nucleation event, the model captured the key qualitative behaviour of the system well. Furthermore, its prediction of the organic volume fraction in newly formed particles, suggesting values as high as 0.5 for 3–4 nm particles and approximately 0.8 for 10 nm particles, agrees with recent indirect composition measurements.
Early unusual ozone loss during the Arctic winter 2002/2003 compared to other winters
Authors: Goutail F. , Pommereau J.-P. , Lefèvre F. , Van Roozendael M. , Andersen S. B. , Kåstad Høiskar B. A. , Dorokhov V. , Kyrö E. , Chipperfield M. P. , Feng W.
Published: April 2010

Abstract. Total column ozone reduction in the Arctic is evaluated each winter since 1993/1994 by the transport method (3-D CTM passive ozone minus measurements). The cumulative loss from 1 December to the end of the season ranges from 5–10% during warm winters like 1998/1999, 2000/2001 and 2001/2002 up to 30%–32% during cold winters like 1994/1995 and 1995/1996. The 23% cumulative loss observed during the winter 2002/2003 is similar in amplitude to the 20–24% measured in 1996/1997 and 1999/2000 but the timing is different. It started unusually early in December after the occurrence of very low temperature at all stratospheric levels between 550 K and 435 K allowing PSC formation and thus chlorine activation. The early ozone loss of 2002/2003 is well captured by current 3-D CTM models.
Three-dimensional model study of the arctic ozone loss in 2002/2003 and comparison with 1999/2000 and 2003/2004
Authors: Feng W. , Chipperfield M. P. , Davies S. , Sen B. , Toon G. , Blavier J. F. , Webster C. R. , Volk C. M. , Ulanovsky A. , Ravegnani F. , von der Gathen P. , Jost H. , Richard E. C. , Claude H.
Published: April 2010

Abstract. We have used the SLIMCAT 3-D off-line chemical transport model (CTM) to quantify the Arctic chemical ozone loss in the year 2002/2003 and compare it with similar calculations for the winters 1999/2000 and 2003/2004. Recent changes to the CTM have improved the model's ability to reproduce polar chemical and dynamical processes. The updated CTM uses σ-θ as a vertical coordinate which allows it to extend down to the surface. The CTM has a detailed stratospheric chemistry scheme and now includes a simple NAT-based denitrification scheme in the stratosphere. In the model runs presented here the model was forced by ECMWF ERA40 and operational analyses. The model used 24 levels extending from the surface to ~55 km and a horizontal resolution of either 7.5°×7.5° or 2.8°×2.8°. Two different radiation schemes, MIDRAD and the CCM scheme, were used to diagnose the vertical motion in the stratosphere. Based on tracer observations from balloons and aircraft, the more sophisticated CCM scheme gives a better representation of the vertical transport in this model which includes the troposphere. The higher resolution model generally produces larger chemical O3 depletion, which agrees better with observations. The CTM results show that very early chemical ozone loss occurred in December 2002 due to extremely low temperatures and early chlorine activation in the lower stratosphere. Thus, chemical loss in this winter started earlier than in the other two winters studied here. In 2002/2003 the local polar ozone loss in the lower stratosphere was ~40% before the stratospheric final warming. Larger ozone loss occurred in the cold year 1999/2000 which had a persistently cold and stable vortex during most of the winter. For this winter the current model, at a resolution of 2.8°×2.8°, can reproduce the observed loss of over 70% locally. In the warm and more disturbed winter 2003/2004 the chemical O3 loss was generally much smaller, except above 620 K where large losses occurred due to a period of very low minimum temperatures at these altitudes.
A re-evaluation of the ClO/Cl2O2 equilibrium constant based on stratospheric in-situ observations
Authors: von Hobe M. , Grooß J.-U. , Müller R. , Hrechanyy S. , Winkler U. , Stroh F.
Published: April 2010

Abstract. In-situ measurements of ClO and its dimer carried out during the SOLVE II/VINTERSOL-EUPLEX and ENVISAT Validation campaigns in the Arctic winter 2003 suggest that the thermal equilibrium between the dimer formation and dissociation is shifted significantly towards the monomer compared to the current JPL 2002 recommendation. Detailed analysis of observations made in thermal equilibrium was used to re-evaluate the magnitude and temperature dependence of the equilibrium constant. A fit of the JPL format for equilibrium constants yields KEQ=4.06×10−23exp(6201/T), but to reconcile the observations made at low temperatures with the existing laboratory studies at room temperature, a modified equation, KEQ=2.31×10−13(T/300)−34.9exp( −1118/T), is required. This format can be rationalised by a strong temperature dependence of the reaction enthalpy possibly induced by Cl2O2 isomerism effects. At stratospheric temperatures, both equations are practically equivalent. Using the equilibrium constant reported here rather than the JPL 2002 recommendation in atmospheric models does not have a large impact on simulated ozone loss. Solely at large zenith angles after sunrise, a small decrease of the ozone loss rate due to the ClO dimer cycle and an increase due to the ClO-BrO cycle (attributed to the enhanced equilibrium ClO concentrations) is observed, the net effect being a slightly stronger ozone loss rate. The effects of Cl2O2 isomerism are not studied in detail, but the presence of isomers other than ClOOCl would be expected to lead to reduced ozone loss.
A review of biomass burning emissions part III: intensive optical properties of biomass burning particles
Authors: Reid J. S. , Eck T. F. , Christopher S. A. , Koppmann R. , Dubovik O. , Eleuterio D. P. , Holben B. N. , Reid E. A. , Zhang J.
Published: April 2010

Abstract. Because of its wide coverage over much of the globe, biomass burning has been widely studied in the context of direct radiative forcing. Such study is warranted as smoke particles scatter and at times absorb solar radiation efficiently. Further, as much of what is known about smoke transport and impacts is based on remote sensing measurements, the optical properties of smoke particles have far reaching effects into numerous aspects of biomass burning studies. Global estimates of direct forcing have been widely varying, ranging from near zero to −1 Wm−2. A significant part of this difference can be traced to varying assumptions on the optical properties of smoke. This manuscript is the third part of four examining biomass-burning emissions. Here we review and discuss the literature concerning measurement and modeling of optical properties of biomass-burning particles. These include available data from published sensitivity studies, field campaigns, and inversions from the Aerosol Robotic Network (AERONET) of Sun photometer sites. As a whole, optical properties reported in the literature are varied, reflecting both the dynamic nature of fires, variations in smoke aging processes and differences in measurement technique. We find that forward modeling or "internal closure" studies ultimately are of little help in resolving outstanding measurement issues due to the high degree of degeneracy in solutions when using "reasonable" input parameters. This is particularly notable with respect to index of refraction and the treatment of black carbon. Consequently, previous claims of column closure may in fact be more ambiguous. Differences between in situ and retrieved ωo values have implications for estimates of mass scattering and mass absorption efficiencies. In this manuscript we review and discuss this community dataset. Strengths and lapses are pointed out, future research topics are prioritized, and best estimates and uncertainties of key smoke particle parameters are provided.
Subtropical trace gas profiles determined by ground-based FTIR spectroscopy at Izaña (28° N, 16° W): Five-year record, error analysis, and comparison with 3-D CTMs
Authors: Schneider M. , Blumenstock T. , Chipperfield M. P. , Hase F. , Kouker W. , Reddmann T. , Ruhnke R. , Cuevas E. , Fischer H.
Published: April 2010

Abstract. Within the framework of the NDSC (Network for the Detection of Stratospheric Change) ground-based FTIR solar absorption spectra have been routinely recorded at Izaña Observatory (28° N, 16° W) on Tenerife Island since March 1999. By analyzing the shape of the absorption lines, and their different temperature sensitivities, the vertical distribution of the absorbers can be retrieved. Unique time series of subtropical profiles of O3, HCl, HF, N2O, and CH4 are presented. The effects of both dynamical and chemical annually varying cycles can be seen in the retrieved profiles. These include enhanced upwelling and photochemistry in summer and a more disturbed atmosphere in winter, which are typical of the subtropical stratosphere. A detailed error analysis has been performed for each profile. The output from two different three-dimensional (3-D) chemical transport models (CTMs), which are forced by ECMWF analyses, are compared to the measured profiles. Both models agree well with the measurements in tracking abrupt variations in the atmospheric structure, e.g. due to tropical streamers, in particular for the lower stratosphere. Simulated and measured profiles also reflect similar dynamical and chemical annual cycles. However, the differences between their mixing ratios clearly exceed the error bars estimated for the measured profiles. Possible reasons for this are discussed.
Intercomparison of stratospheric ozone and temperature measurements at the Observatoire de Haute Provence during the OTOIC NDSC validation campaign from 1–18 July 1997
Authors: Braathen G. O. , Godin-Beekmann S. , Keckhut P. , McGee T. J. , Gross M. R. , Vialle C. , Hauchecorne A.
Published: April 2010

Abstract. The OHP Temperature and Ozone Intercomparison Campaign (OTOIC) took place at the Observatoire de Haute Provence, France, from 1–18 July 1997. The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire de Haute Provence (OHP) during a blind intercomparison as a part of the continuous validation process within the Network for the Detection of Stratospheric Change. The GSFC measurements were compared to two lidars permanently deployed at OHP and operated by the Centre National de la Recherche Scientifique (CNRS), one measuring ozone and the other measuring temperature.
Single particle analysis of the accumulation mode aerosol over the northeast Amazonian tropical rain forest, Surinam, South America
Authors: Krejci R. , Ström J. , de Reus M. , Sahle W.
Published: April 2010

Abstract. Single particle analysis of aerosols particles larger than 0.2 µm diameter was performed on 24 samples collected over Surinam tropical rain forest and in the adjacent marine boundary layer (MBL) during the LBA-CLAIRE 98 campaign in March 1998. Elemental composition and morphology of 2308 particles was determined using SEM-EDX. The aerosol particles were divided into seven groups according to their chemical composition: organic particles, mineral dust, aged mineral dust, sea salt, aged sea salt, Ca-rich, and biogenic aerosol. Samples were further divided with respect to the distinct atmospheric layers present in the tropical troposphere including MBL, continental mixed layer, cloud convective layer, free troposphere and region of deep convection outflow. The organic and mineral dust particles are two major groups observed over the rainforest. In the MBL also sea salt particles represented a large fraction between 15 and 27%. The organic particles control much of the chemical characteristic of the aerosol in the continental tropical troposphere. Their abundance ranged from less than 20% in the MBL to more than 90% in the free troposphere between 4.5 and 12.6 km altitude. During the transport of the air masses from the MBL over the rain forest, fraction of organic aerosol particles more than doubled, reaching 40-60% in the continental boundary layer. This increase was attributed to direct emissions of biogenic aerosols from the tropical vegetation. The high fraction of the organic accumulation mode particles in the upper tropical troposphere could be a good indicator for the air masses originated over the tropical rain forest.
High resolution mid-infrared cross-sections for peroxyacetyl nitrate (PAN) vapour
Authors: Allen G. , Remedios J. J. , Newnham D. A. , Smith K. M. , Monks P. S.
Published: April 2010

Abstract. Absorption spectra of peroxyacetyl nitrate (PAN, CH3C(O)OONO2) vapour at room temperature (295 K) have been measured in the mid-infrared range, 550–2200 cm−1 (18.2–3.33 µm), using a Fourier transform infrared spectrometer at instrument resolutions of 0.25 and 0.03 cm−1 (unapodised). Both cross-section data and integrated absorption intensities for the five principal bands in the PAN spectra in this spectral range have been derived from fourteen separate PAN transmission spectra measurements. Band intensities and band centre absorptivities are also reported for four weaker PAN absorption bands in the mid infrared for the first time. These observations are the highest spectral resolution measurements of PAN bands recorded in the infrared to date. For three of the five strongest bands, the absolute integrated absorption intensities are in excellent agreement with previous studies. A 4.8% lower integrated intensity was found for the 1741 cm−1 νas (NO2) PAN absorption band, possibly as a result of the removal in this work of spectra affected by subtle acetone contamination, while a 10.6% higher intensity was determined for the 1163 cm−1 ν (C-O) absorption band. No direct effects of spectral resolution were observed. The improved accuracy of these absorption cross-sections will allow more accurate investigations of PAN using infrared spectroscopy, particularly for remote sensing of PAN in the atmosphere.
Estimating the impact of natural and anthropogenic emissions on cloud chemistry: the influence of organic compounds
Authors: Alfonso L. , Raga G. B.
Published: April 2010

Abstract. In order to estimate the anthropogenic influence of gas and aerosol emissions from the Petroleum Industry in maritime zones with clouds of small vertical extent, a numerical 1D Eulerian cloud-chemical model with detailed microphysics (Alfonso and Raga, 2002) is used to simulate the influence of water soluble organic compounds (WSOC) and organic+inorganic gas emissions on cloud development. Following Mircea et al. (2002), we tested the sensitivity of the cloud and precipitation development in the classical inorganic case (CIC) and the inorganic+organic case (IOC) with respect to CCN compositions. The results indicate an increase in the droplet concentration for the IOC, and a delay in the development of precipitation. The pH spectral evolution was studied during both the development and precipitation stages. The influence of the diffusion of formic acid and its generation by oxidation of hydrated formaldehyde in the aqueous phase result in a reduction in the pH of precipitation in the range between 0.05 and 0.15 pH units (from 1 to 3%) for the high ambient SO2 concentration (20 ppb) and between 0.2–0.5 pH units (from 4 to 10%) for the low ambient SO2 concentration (1 ppb) case.
The effects of lightning-produced NOx and its vertical distribution on atmospheric chemistry: sensitivity simulations with MATCH-MPIC
Authors: Labrador L. J. , von Kuhlmann R. , Lawrence M. G.
Published: April 2010

Abstract. The impact of different assumptions concerning the source magnitude as well as the vertical placement of lightning-produced nitrogen oxides is studied using the global chemistry transport model MATCH-MPIC. The responses of NOx, O3, OH, HNO3 and peroxyacetyl-nitrate (PAN) are investigated. A marked sensitivity to both parameters was found. NOx burdens globally can be enhanced up to 100% depending on the vertical placement and source magnitude strength. In all cases, the largest enhancements occur in the tropical upper troposphere, where lifetimes of most trace gases are longer and where they thus become more susceptible to long-range transport by long-range circulation patterns. Comparison with observations indicate that the 0 and 20 Tg/yr(N) production rates of NOx from lightning are too low and too high a source magnitude, respectively. However, no single intermediate production rate or vertical distribution can be singled out as best fitting the observations due to the large scatter in the datasets. This underscores the need for further measurement campaigns in key regions. The vertical profiles of Pickering et al. (1998) have been implemented in MATCH-MPIC for this study.
Is there a trend in cirrus cloud cover due to aircraft traffic?
Authors: Stordal F. , Myhre G. , Arlander W. , Svendby T. , Stordal E. J. G. , Rossow W. B. , Lee D. S.
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 could cover due to aircraft traffic. Main emphasis has been on the area covered by the METEOSAT satellite, to avoid trends in the ISCCP data resulting from changing satellite positions. An alternative retrieval of high clouds in this region has been used to complement the analysis based on ISCCP data. In Europe, which is within the METEOSAT region, we find indications of a trend of about 2%/decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic seems to have contrasted 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 best estimate of 0.05 Wm−2 for the radiative forcing due to aircraft. This is close to the value given by IPCC (1999) as an upper limit.
Refinements in the use of equivalent latitude for assimilating sporadic inhomogeneous stratospheric tracer observations, 2: Precise altitude-resolved information about transport of Pinatubo aerosol to very high latitude
Authors: Good P. , Pyle J.
Published: April 2010

Abstract. From high latitude lidar observations, quite precise information is extracted about the temporal evolution and vertical distribution of volcanic aerosol in the high latitude lower stratosphere following the eruption of Mount Pinatubo. Irreversible mixing of lower stratospheric aerosol, to the arctic pole during early 1992, is demonstrated, as a function of potential temperature and time. This work complements previous studies, which either identify vortex intrusions – without demonstrating irreversible transport, or use lower resolution satellite observations. The observed transport is associated tentatively with the vortex disturbance during late January 1992. A very large number of high resolution lidar observations of Mount Pinatubo aerosol are analysed, without any data averaging. Averaging in measurement or analysis can cause tracer mixing to be overestimated. Averaging in the analysis can also require assumptions about which quantity has the dominant error (in this case, the equivalent latitude coordinate or the measurement), and which part of the data contains real structure. The method below attempts to avoid such assumptions.
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 74% and 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.
Technical Note: The Modular Earth Submodel System (MESSy) – a new approach towards Earth System Modeling
Authors: Jöckel P. , Sander R. , Lelieveld J.
Published: April 2010

Abstract. Generally, the typical approach towards Earth System Modeling has been to couple existing models of different domains (land, ocean, atmosphere, ...) offline, using output files of one model to provide input for the other. However, for a detailed study of the interactions and feedbacks between chemical, physical, and biological processes, it is necessary to perform the coupling online. One strategy is to link the existing domain-specific models with a universal coupler. In many cases, however, a much simpler approach is more feasible. To achieve the online coupling, we have developed the Modular Earth Submodel System (MESSy). Data are exchanged between a and several within one comprehensive model system. MESSy includes a generalized interface structure for the standardized control of the and their interconnections. The internal complexity of the is controllable in a transparent and user friendly way. This provides remarkable new possibilities to study feedback mechanisms (by two-way coupling), e.g., by applying MESSy to a general circulation model (GCM).
Modelling the impact of noctilucent cloud formation on atomic oxygen and other minor constituents of the summer mesosphere
Authors: Murray B. J. , Plane J. M. C.
Published: April 2010

Abstract. The formation, evolution and eventual sublimation of noctilucent clouds (NLC) could have a significant effect on the odd oxygen and hydrogen chemistry of the high latitude summer mesosphere. Three mechanisms are considered here: the direct uptake of atomic oxygen on the surface of the ice particles; the redistribution of water vapour, which changes the photochemical source of odd hydrogen species; and the direct photolysis of the ice particles themselves to produce odd hydrogen species in the gas phase. A 1-D photochemical model is employed to investigate the potential importance of these mechanisms. This shows, using the recently measured uptake coefficients of O on ice, that the heterogeneous removal of O on the surface of the cloud particles is too slow by at least a factor of 5×103 to compete with gas-phase O chemistry. The second and third mechanisms involve the solar Lyman-α photolysis of H2O in the gas and solid phase, respectively. During twilight, Lyman-α radiation is severely attenuated and these mechanisms are insignificant. In contrast, when the upper mesosphere is fully illuminated there is a dramatic impact on the O profile, with depletion of O at the base of the cloud layer of close to an order of magnitude. A correspondingly large depletion in O3 is also predicted, while H, OH, HO2 and H2O2 are found to be enhanced by factors of 3–5. In fact, rocket-borne mass spectrometer measurements during summer have revealed local H2O2 enhancements in the region of the clouds. Rocket-borne measurements of atomic O and O3 profiles in the presence of mesospheric clouds in the daytime are highly desirable to test the predictions of this model and our understanding of the genesis of mesospheric clouds.
Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration
Authors: Jensen E. , Smith J. B. , Pfister L. , Pitman J. V. , Weinstock E. M. , Sayres D. S. , Herman R. L. , Troy R. F. , Troy K. , Thompson T. L. , Fridlind A. , Hudson P. , Cziczo D. J. , Heymsfield A. J. , Schmitt C. , Wilson J. C.
Published: April 2010

Abstract. Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of sulfate aerosol freezing. The high supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values at least 20% too low, (2) most of the available aerosols had a composition that makes them much more resistant to ice nucleation than aerosols used in laboratory experiments, and (3) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if these decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere.
Validation of SCIAMACHY tropospheric NO2-columns with AMAXDOAS measurements
Authors: Heue K.-P. , Richter A. , Wagner T. , Bruns M. , Burrows J. P. , v. Friedeburg C. , Lee W. D. , Platt U. , Pundt I. , Wang P.
Published: April 2010

Abstract. Vertical and slant tropospheric NO2-columns from the new satellite instrument SCIAMACHY on ENVISAT are validated by measurements of the Airborne Multi AXis DOAS (AMAXDOAS) instrument on board the DLR Falcon. The results presented here were obtained in February 2003 on a flight over the Alps, the Po-Valley and the Mediterranean. The tropospheric vertical column measured by AMAXDOAS varied between 12.8 and 27.2*1015 molec/cm2 over the Po-Valley where SCIAMACHY data resulted in 14.4 to 27.5*1015 molec/cm2. Over less polluted areas a similarly good agreement was found. The overall correlation between the two datasets results in a slope of the linear fit of 0.89. The slight differences observed might be attributed to the different spatial resolution and the temporal mismatch between the measurements over the Po-Valley.
Application of osmolality for the determination of water activity and the modelling of cloud formation
Authors: Kiss G. , Hansson H.-C.
Published: April 2010

Abstract. A simple approach is suggested here to give reliable estimates on the Raoult term of the Köhler equation when calculating critical supersaturation (Sc) for real atmospheric samples. Water activity is calculated from osmolality and thus the original Köhler equation can be applied avoiding the difficulties with unknown molecular weights, solubilities, van't Hoff factors of aerosol constituents and also the interactions in the growing droplet. First, water activity calculated from osmolality data was compared to literature values both for electrolytes and a non-electrolyte. Then the applicability of the approach was demonstrated by generating Köhler curves from osmolality derived and literature activity data as well as by using the simplified Köhler equation. Sc values calculated with the osmolality approach fitted those obtained by using literature water activity data within a relative deviation of less than 0.3%, 0.8%, 1.1% and 3.4% for sucrose, CaCl2, NaCl and H2SO4, respectively, while the corresponding errors with the simplified Köhler equation were 11%, 8.5%, 4.5% and 19% in the dry nucleus size range of 20 nm to 100 nm. Finally, the osmolality method was used to show how considerably Sc is underestimated for organic acids if complete dissociation is assumed. The method described in this paper can be applied to real atmospheric samples (aerosol extracts, fog water or cloud water) thus improving the reliability of estimates on critical supersaturation and critical droplet diameter in atmospheric modelling.
Meteor science from regular incoherent scatter radar ionospheric observations at Arecibo
Authors: Sulzer M. P.
Published: April 2010

Abstract. We report the observation and analysis of ionization flashes associated with the decay of meteoroids (so-called head echos) detected by the Arecibo 430 MHz radar during regular ionospheric observations in the spring and autumn equinoxes. These two periods allow pointing well-above and nearly-into the ecliptic plane at dawn when the event rate maximizes. The observation of many thousands of events allows a statistical interpretation of the results, which show that there is a strong tendency for the observed meteoroids to come from the apex as has been previously reported (Chau and Woodman, 2003). The velocity distributions agree with Janches et al. (2003) when they are directly comparable, but the azimuth scan used in these observations allows a new perspective. We have constructed a simple statistical model which takes meteor velocities as input and gives radar line of sight velocities as output. The intent is to explain the fastest part of the velocity distribution. Since the speeds interpreted from the measurements are distributed fairly narrowly about nearly 60 km/s−1, double the speed of the earth in its orbit, the obvious interpretation is that many of the meteoroids seen by the Arecibo radar are moving in orbits about the sun with similar parameters as the earth, but in the retrograde direction. However, some aspects of the measured velocity distributions suggest that this is not a complete description even for the fast part of the distribution, and it certainly says nothing about the slow part first described in Janches et al. (2003). Furthermore, we cannot conclude anything about the entire dust population since there are probably selection effects that restrict the observations to a subset of the population.
Quantification of mesoscale transport across the boundaries of the free troposphere: a new method and applications to ozone
Authors: Gheusi F. , Cammas J.-P. , Cousin F. , Mari C. , Mascart P.
Published: April 2010

Abstract. A new Lagrangian method is proposed to quantify the transport of ozone – or any other atmospheric constituent – by objectively-defined air-masses. In the framework of mesoscale modelling, this method is an alternative to classical Eulerian or trajectory-based methods, which suffer from many drawbacks at this scale. The elementary air-parcels are tagged with their initial location (what is made possible in the model by passive transport of three tracer fields initialized with the space coordinates). This enables to retrieve not only their back-trajectories but also their physical and chemical history. This information is in turn used to relevantly define transporting air-masses along objective criteria. For instance the ozone mass that has left the planetary boundary layer (PBL) to intrude the free troposphere (FT) in a given time interval, is carried by the ensemble of air-parcels that were initially in the PBL but are finally in the FT. Such an air-mass can be characterized by e.g., a criterion on the initial and final values of the turbulent kinetic energy of the air-parcels. The last step to obtain the sought ozone mass is a simple spatial integration of the ozone concentration over the so-defined air-mass. Two case-studies are presented as illustrations with increasing complexity: (i) the downward transport of ozone accompanying a tropopause fold, across a mid-tropospheric altitude level; (ii) a case of PBL-to-FT transport, as evoked above.
Actinometric measurements of NO2 photolysis frequencies in the atmosphere simulation chamber SAPHIR
Authors: Bohn B. , Rohrer F. , Brauers T. , Wahner A.
Published: April 2010

Abstract. The simulation chamber SAPHIR at Forschungszentrum Jülich has UV permeable teflon walls facilitating atmospheric photochemistry studies under the influence of natural sunlight. Because the internal radiation field is strongly affected by construction elements, we use external, radiometric measurements of spectral actinic flux and a model to calculate mean photolysis frequencies for the chamber volume (Bohn and Zilken, 2004). In this work we determine NO2 photolysis frequencies j(NO2) within SAPHIR using chemical actinometry by injecting NO2 and observing the chemical composition during illumination under various external conditions. In addition to a photo-stationary approach, a time-dependent method was developed to analyse the data. These measurements had two purposes. Firstly, to check the model predictions with respect to diurnal and seasonal variations in the presence of direct sunlight and secondly to obtain an absolute calibration factor for the combined radiometry-model approach. We obtain a linear correlation between calculated and actinometric j(NO2). A calibration factor of 1.34±0.10 is determined, independent of conditions in good approximation. This factor is in line with expectations and can be rationalised by internal reflections within the chamber. Taking into account the uncertainty of the actinometric j(NO2), an accuracy of 13% is estimated for the determination of j(NO2) in SAPHIR. In separate dark experiments a rate constant of (1.93±0.12)×10−14 cm3 s−1 was determined for the NO+O3 reaction at 298 K using analytical and numerical methods of data analysis.
The impact of anthropogenic chlorine, stratospheric ozone change and chemical feedbacks on stratospheric water
Authors: Röckmann T. , Grooß J.-U. , Müller R.
Published: April 2010

Abstract. Mixing ratios of water (H2O) in the stratosphere appear to increase due to increased input of H2O and methane (CH4) from the troposphere and due to intensified oxidation of CH4 in the stratosphere, but the underlying mechanisms are not yet understood. Here we identify and quantify three chemical mechanisms which must have led to more efficient oxidation of CH4 over the past several decades: 1) The increase in stratospheric chlorine levels due to anthropogenic CFC emissions, 2) the thinning of the stratospheric ozone column and 3) enhanced OH levels in the stratosphere due to increasing H2O levels themselves. In combination with the increase in tropospheric CH4 mixing ratios and with solar cycle related variations of upper stratospheric ozone, these effects can explain about 50% of the additional conversion of CH4 to H2O as observed throughout the stratosphere. The relative contributions from the individual processes have varied over the past decades.
The UV-A and visible solar irradiance spectrum: inter-comparison of absolutely calibrated, spectrally medium resolution solar irradiance spectra from balloon- and satellite-borne measurements
Authors: Gurlit W. , Bösch H. , Bovensmann H. , Burrows J. P. , Butz A. , Camy-Peyret C. , Dorf M. , Gerilowski K. , Lindner A. , Noël S. , Platt U. , Weidner F. , Pfeilsticker K.
Published: April 2010

Abstract. Within the framework of the ENVISAT/-SCIAMACHY satellite validation, solar irradiance spectra are absolutely measured at moderate resolution in the UV/visible spectral range (in the UV from 316.7–418 nm and the visible from 400–652 nm at a full width half maximum resolution of 0.55 nm and 1.48 nm, respectively) from aboard the azimuth-controlled LPMA/DOAS balloon gondola at around 32 km balloon float altitude. After accounting for the atmospheric extinction due to Rayleigh scattering and gaseous absorption (O3, and NO2), the measured solar spectra are compared with previous observations. Our solar irradiance is +1.6% larger than the re-calibrated Kurucz et al. (1984) solar spectrum (Fontenla et al., 1999, called MODTRAN 3.5) in the visible spectral range (435–650 nm), +1.5% larger in the (370–415 nm) wavelength interval, but −4% smaller in the UV spectral range (316.7–370 nm), when the Kurucz spectrum is convolved to the spectral resolution of our instrument. The same comparison with the SOLSPEC solar spectrum (Thuillier et al., 1997, 1998a, b) confirms the somewhat larger solar irradiance (+1.7%) measured by the balloon instrument from 435–500 nm, but not from 500–650 nm, where the SOLSPEC is −1.3% lower than MODTRAN 3.5. Comparison of the SCIAMACHY solar spectrum from channels 1 to 4 (– re-calibrated by the University of Bremen –) with MODTRAN 3.5 indicates an agreement of +0.2% in the visible spectral range (435–585 nm). With this calibration, the SCIAMACHY solar spectrum is congruent with the balloon observations (−1%) in the 316.7–370 nm wavelength range, but both are up to −5%/−3% smaller than MODTRAN 3.5 and SOLSPEC, respectively. In agreement with findings of Skupin et al. (2002) our study emphasizes that the present ESA SCIAMACHY level 1 calibration is systematically +15% larger in the considered wavelength intervals when compared to all available other solar irradiance measurements.
CLABAUTAIR: a new algorithm for retrieving three-dimensional cloud structure from airborne microphysical measurements
Authors: Scheirer R. , Schmidt S.
Published: April 2010

Abstract. A new algorithm is presented to retrieve the three-dimensional structure of clouds from airborne measurements of microphysical parameters. Data from individual flight legs are scanned for characteristic patterns, and the autocorrelation functions for several directions are used to extrapolate the observations along the flight path to a full three-dimensional distribution of the cloud field. Thereby, the mean measured profiles of microphysical parameters are imposed to the cloud field by mapping the measured probability density functions onto the model layers. The algorithm was tested by simulating flight legs through synthetic clouds (by means of Large Eddy Simulations (LES)) and applied to a stratocumulus cloud case measured during the first field experiment of the EC project INSPECTRO (INfluence of clouds on the SPECtral actinic flux in the lower TROposphere) in East Anglia, UK. The number and position of the flight tracks determine the quality of the retrieved cloud field. If they provide a representative sample of the entire field, the derived pattern closely resembles the statistical properties of the real cloud field.