bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the ice growth rate on the incorporation of gaseous HCl
Authors: Domine F. , Rauzy C.
Published: April 2010

Abstract. Ice crystals were grown in the laboratory at −15°C, at different growth rates and in the presence of a partial pressure of HCl of 1.63×10−3 Pa, to test whether the ice growth rate influences the amount of HCl taken up, XHCl, as predicted by the ice growth mechanism of Domine and Thibert (1996). The plot of HCl concentration in ice as a function of growth rate has the aspect predicted by that mechanism: XHCl decreases with increasing growth rate, from a value that depends on thermodynamic equilibrium to a value that depends only on kinetic factors. The height of the growth steps of the ice crystals is determined to be about 1.5 nm from these experiments. We discuss that the application of these laboratory experiments to cloud ice crystals and to snow metamorphism is not quantitatively possible at this stage, because the physical variables that determine crystal growth in nature, and in particular the step height, are not known. Qualitative applications are attempted for HCl and HNO3 incorporation in cloud ice and snowpack crystals.
The origin of sea salt in snow on Arctic sea ice and in coastal regions
Authors: Domine F. , Sparapani R. , Ianniello A. , Beine H. J.
Published: April 2010

Abstract. Snow, through its trace constituents, can have a major impact on lower tropospheric chemistry, as evidenced by ozone depletion events (ODEs) in oceanic polar areas. These ODEs are caused by the chemistry of bromine compounds, that originate from sea salt bromide. According to current ideas, bromide may be supplied to the snow surface either by upward migration from sea ice or by frost flowers being wind-blown to the snow surface. We investigate here the relative importance of both these processes by analyzing mineral ions in snow samples collected near Alert and Ny-Ålesund (Canadian and European high Arctic) in winter and spring. Vertical ionic profiles in the snowpack on sea ice are measured to test upward migration of sea salt ions and to seek evidence for ion fractionation processes. Time series of the ionic composition of surface snow layers are investigated to quantify wind-transported ions. Upward migration of unfractionated sea salt, to heights of at least 17 cm, was observed in snow sampled in winter, at temperatures near −30°C, leading to Cl− concentration of several hundred µM. Upward migration thus has the potential to supply ions to surface snow layers. Time series show that wind can deposit aerosols to the top few cm of the snow, leading also to Cl− concentrations of several hundred µM, so that both migration from sea ice and wind transport can significantly contribute ions to snow. At Ny-Ålesund, sea salt transported by wind was unfractionated, implying that it does not come from frost flowers. In the Arctic, frost flowers thus do not appear necessary to lead to large sea salt concentrations in surface snow, and to supply the bromide needed for ODEs. The data obtained also indicate that ODEs lead to significant deposition of Br− to snow. We speculate that this can also take place in coastal regions and contribute to propagate ODEs inland. Finally, we stress the need to measure snow physical parameters such as permeability and specific surface area, to understand quantitatively changes in snow chemistry.
Evaluation of SHADOZ sondes, HALOE and SAGE II ozone profiles at the tropics from SAOZ UV-Vis remote measurements onboard long duration balloons
Authors: Borchi F. , Pommereau J.-P. , Garnier A. , Pinharanda M.
Published: April 2010

Abstract. Long series of ozone profiles from 6 to 28 km at the Southern Tropics have been obtained from solar occultation measurements at twilight using a SAOZ spectrometer borne by long duration balloons. Two flights have been performed from Bauru in Brazil both in the summer, in February and March 2001 and 2003, from where the balloons are moving westward at almost constant latitude (20°±5° S). The flight in 2001 passed right over Reunion Island where the SAOZ measurements could be compared to those of both tropospheric and stratospheric ozone lidars. In the stratosphere, compared to that of SAOZ, the measurements of the SHADOZ ozonesondes network, and the HALOE and SAGE II instruments in orbit are found a little noisier (2–3% for SAGE II, 3–4% for HALOE, 4–5% for the sondes), and of insignificant or small high biased (SAGE II). No differences in altitude could be found between SAOZ and SAGE II at all levels, and HALOE above 22 km. But the ozonesondes appear to be systematically displaced upwards by some 400–700 m at all levels, and the HALOE profiles do show an increasing altitude bias at decreasing altitude below 22 km. In the upper troposphere, the SAOZ measurements are found consistent with those of the sondes at Reunion Island and high biased on average over the Western Pacific, at American Samoa and Fiji. Compared to SAOZ, SAGE II shows a 50–60% low bias similar to that already found with the ozonesondes, and a 2–2.5 times larger zonal variability, suggesting a degradation of its precision below the tropopause. Finally, the unrealistic large offsets and variability in the HALOE data compared to all others suggest that its measurements are no reliable in the tropical troposphere below 17 km.
Observations of oxidation products above a forest imply biogenic emissions of very reactive compounds
Authors: Holzinger R. , Lee A. , Paw U K. T. , Goldstein A. H.
Published: April 2010

Abstract. Measurements of volatile organic compounds in a pine forest (Central California, 38.90° N, 120.63° W, 1315 m) reveal large quantities of previously unreported oxidation products of short lived biogenic precursors. The emission of biogenic precursors must be in the range of 13–66 µmol m−2 h−1 to produce the observed oxidation products. That is 6–30 times the emissions of total monoterpenes observed above the forest canopy on a molar basis. These reactive precursors constitute the largest fraction of biogenic emissions at this site, and are not included in current emission inventories. When oxidized by ozone they should efficiently produce secondary aerosol and hydroxyl radicals.
Atmospheric pseudohalogen chemistry
Authors: Lary D. J.
Published: April 2010

Abstract. There are at least three reasons why hydrogen cyanide is likely to be significant for atmospheric chemistry. The first is well known, HCN is a product and marker of biomass burning. However, if a detailed ion chemistry of lightning is considered then it is almost certain than in addition to lightning producing NOx, it also produces HOx and HCN. Unlike NOx and HOx, HCN is long-lived and could therefore be a useful marker of lightning activity. Observational evidence is considered to support this view. Thirdly, the chemical decomposition of HCN leads to the production of small amounts of CN and NCO. NCO can be photolyzed in the visible portion of the spectrum yielding N atoms. The production of N atoms is significant as it leads to the titration of nitrogen from the atmosphere via N+N→N2. Normally the only modelled source of N atoms is NO photolysis which happens largely in the UV Schumann-Runge bands. However, NCO photolysis occurs in the visible and so could be involved in titration of atmospheric nitrogen in the lower stratosphere and troposphere. HCN emission inventories are worthy of attention. The CN and NCO radicals have been termed pseudohalogens since the 1920s. They are strongly bound, univalent, radicals with an extensive and varied chemistry. The products of the atmospheric oxidation of HCN are NO, CO and O3. N+CH4 and N+CH3OH are found to be important sources of HCN. Including the pseudohalogen chemistry gives a small increase in ozone and total reactive nitrogen (NOy).
The aerosol-climate model ECHAM5-HAM
Authors: Stier P. , Feichter J. , Kinne S. , Kloster S. , Vignati E. , Wilson J. , Ganzeveld L. , Tegen I. , Werner M. , Balkanski Y. , Schulz M. , Boucher O.
Published: April 2010

Abstract. The aerosol-climate modelling system ECHAM5-HAM is introduced. It is based on a flexible microphysical approach and, as the number of externally imposed parameters is minimised, allows the application in a wide range of climate regimes. ECHAM5-HAM predicts the evolution of an ensemble of microphysically interacting internally- and externally-mixed aerosol populations as well as their size-distribution and composition. The size-distribution is represented by a superposition of log-normal modes. In the current setup, the major global aerosol compounds sulfate (SU), black carbon (BC), particulate organic matter (POM), sea salt (SS), and mineral dust (DU) are included. The simulated global annual mean aerosol burdens (lifetimes) for the year 2000 are for SO4: 0.80 Tg(S) (3.9 days), for BC: 0.11 Tg (5.4 days), for POM: 0.99 Tg (5.4 days), for SS: 10.5 Tg (0.8 days), and for DU: 8.28 Tg (4.6 days). An extensive evaluation with in-situ and remote sensing measurements underscores that the model results are generally in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is with 0.14 in excellent agreement with an estimate derived from AERONET measurements (0.14) and a composite derived from MODIS-MISR satellite retrievals (0.16). Regionally, the deviations are not negligible. However, the main patterns of AOD attributable to anthropogenic activity are reproduced.
Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons
Authors: Bloss C. , Wagner V. , Jenkin M. E. , Volkamer R. , Bloss W. J. , Lee J. D. , Heard D. E. , Wirtz K. , Martin-Reviejo M. , Rea G. , Wenger J. C. , Pilling M. J.
Published: April 2010

Abstract. The Master Chemical Mechanism has been updated from MCMv3 to MCMv3.1 in order to take into account recent improvements in the understanding of aromatic photo-oxidation. Newly available kinetic and product data from the literature has been incorporated into the mechanism. In particular, the degradation mechanisms for hydroxyarenes have been revised following the observation of high yields of ring-retained products, and product studies of aromatic oxidation under relatively low NOx conditions have provided new information on the branching ratios to first generation products. Experiments have been carried out at the European Photoreactor (EUPHORE) to investigate key subsets of the toluene system. These results have been used to test our understanding of toluene oxidation, and where possible, refine the degradation mechanisms. The evaluation of MCMv3 and MCMv3.1 using data on benzene, toluene, p-xylene and 1,3,5-trimethylbenzene photosmog systems is described in a companion paper, and significant model shortcomings are identified. Ideas for additional modifications to the mechanisms, and for future experiments to further our knowledge of the details of aromatic photo-oxidation are discussed.
Technical Note: Evaporation of polar stratospheric cloud particles, in situ, in a heated inlet
Authors: Eidhammer T. , Deshler T.
Published: April 2010

Abstract. In December 2001 and 2002 in situ aerosol measurements were made from balloon-borne platforms within polar stratospheric clouds (PSC) consisting of supercooled ternary solutions, nitric acid trihydrate and ice. Particle size (radius >0.15 m) and number concentrations were measured with two optical particle counters. One of these included an ~80 cm inlet heated to >244 K to obtain measurements, within PSCs, of the size distribution of the stratospheric particles upon which the PSC particles condensed. These measurements are compared to models that calculate the evaporation of PSC particles. The modeled evaporation for supercooled ternary solutions is in good agreement with the measurements. For nitric acid trihydrate it is uncertain what happens to the particle as it is brought to temperatures >50 K above its equilibrium temperature at stratospheric partial pressures. Here the modeled evaporation show too low evaporation compared to the measurements.
Stratospheric aerosol measurements by dual polarisation lidar
Authors: Vaughan G. , Wareing D. P.
Published: April 2010

Abstract. We present measurements of stratospheric aerosol made at Aberystwyth, UK (52.4° N, 4.06° W) during periods of background aerosol conditions. The measurements were made with a lidar system based on a 532 nm laser and two polarisation channels in the receiver. When stratospheric aerosol amounts are very small, as at present, this method is, potentially, free of a number of systematic errors that bedevil more commonly-used methods. The method rests on the assumption that the aerosol consists of spherical droplets which do not depolarise the lidar signal, which is valid under most conditions. Maximum lidar ratios in background aerosol of 1.03–1.06 were measured during the period 2001–2004, with integrated backscatter in the range 2–7×10−5sr−1. In January 2003, depolarising aerosol was measured, which invalidated the dual-polarisation measurements. On 10–11 January, the depolarising aerosol was clearly a polar stratospheric cloud (the first lidar observations of such clouds in the British Isles) but the aerosol observed on 7–8 January was too low in altitude and too warm to be a PSC.
Improved sky imaging for studies of enhanced UV irradiance
Authors: Sabburg J. M. , Long C. N.
Published: April 2010

Abstract. A recent World Meteorological Organisation report discussed the importance of continued study of the effect of clouds on the solar UV radiation reaching the earth’s surface. The report mentions that the use of all-sky imagery offers the potential to understand and quantify cloud effects more accurately. There are an increasing number of studies investigating the enhancement of surface UV irradiance, and UV actinic flux, using automated CCD and sky imagers. This paper describes new algorithms applicable to a commercially available all-sky imager (TSI-440), for research investigating cloud enhanced spectral UV irradiance. Specifically, these include three new algorithms relating to cloud amount at different spatial positions and the visible brightness of clouds surrounding the sun. A possible relationship between UV enhancement and the occurrence of near-sun cloud brightness is reported. It is found that a range of wavelength dependent intensities, from 306 to 400 nm, can occur in one day for UV enhancements. Evidence of a decreasing variation of intensity with longer wavelengths is also presented.
Oxygenated compounds in aged biomass burning plumes over the Eastern Mediterranean: evidence for strong secondary production of methanol and acetone
Authors: Holzinger R. , Williams J. , Salisbury G. , Klüpfel T. , de Reus M. , Traub M. , Crutzen P. J. , Lelieveld J.
Published: April 2010

Abstract. Airborne measurements of acetone, methanol, PAN, acetonitrile (by Proton Transfer Reaction Mass Spectrometry), and CO (by Tunable Diode Laser Absorption Spectroscopy) have been performed during the Mediterranean Intensive Oxidants Study (MINOS, August 2001). In the course of the campaign 10 biomass burning plumes, identified by strongly elevated acetonitrile mixing ratios, were found. The characteristic biomass burning signatures obtained from these plumes reveal secondary production of acetone and methanol, while CO photochemically declines in the plumes. Mean excess mixing ratios – normalized to CO – of 1.8%, 0.20%, 3.8%, and 0.65% for acetone, acetonitrile, methanol, and PAN, respectively, were found in the plumes. By scaling to an assumed global annual source of 663–807 Tg CO, biomass burning emissions of 25–31 and 29–35 Tg/yr for acetone and methanol are estimated, respectively. Our measurements suggest that the present biomass burning contributions of acetone and methanol are significantly underestimated due to the neglect of secondary formation. Median acetonitrile mixing ratios throughout the troposphere were around 150 pmol/mol; this is in accord with current biomass burning inventories and an atmospheric lifetime of ~6 months.
Parametric sensitivity and uncertainty analysis of dimethylsulfide oxidation in the remote marine boundary layer
Authors: Lucas D. D. , Prinn R. G.
Published: April 2010

Abstract. A study of the current significant uncertainties in dimethylsulfide (DMS) gas-phase chemistry provides insight into additional research needed to decrease these uncertainties. The DMS oxidation cycle in the remote marine boundary layer is simulated using a diurnally-varying box model with 56 uncertain chemical and physical parameters. Two analytical methods (direct integration and probabilistic collocation) are used to determine the most influential parameters (sensitivity analysis) and sources of uncertainty (uncertainty analysis) affecting the concentrations of DMS, SO2, methanesulfonic acid (MSA), and H2SO4. The key parameters identified by the sensitivity analysis are associated with DMS emissions, mixing in to and out of the boundary layer, heterogeneous removal of soluble sulfur-containing compounds, and the DMS+OH addition and abstraction reactions. MSA and H2SO4 are also sensitive to the rate constants of numerous other reactions, which limits the effectiveness of mechanism reduction techniques. Propagating the parameter uncertainties through the model leads to concentrations that are uncertain by factors of 1.8 to 3.0. The main sources of uncertainty are from DMS emissions and heterogeneous scavenging. Uncertain chemical rate constants, however, collectively account for up to 50–60% of the net uncertainties in MSA and H2SO4. The concentration uncertainties are also calculated at different temperatures, where they vary mainly due to temperature-dependent chemistry. With changing temperature, the uncertainties of DMS and SO2 remain steady, while the uncertainties of MSA and H2SO4 vary by factors of 2 to 4.
Simulation of stratospheric water vapor trends: impact on stratospheric ozone chemistry
Authors: Stenke A. , Grewe V.
Published: April 2010

Abstract. A transient model simulation from 1960 to 2000 with the coupled climate-chemistry model (CCM) shows a stratospheric water vapor trend during the last two decades of +0.7 ppmv and additionally a short-term increase during volcanic eruptions. At the same time this model simulation shows a long-term decrease in total ozone and a short-term tropical ozone decline after a volcanic eruption. In order to understand the resulting effects of the water vapor changes on stratospheric ozone chemistry, different perturbation simulations have been performed with the CCM with the water vapor perturbations fed only to the chemistry part. Two different long-term perturbations of stratospheric water vapor, +1 ppmv and +5 ppmv, and a short-term perturbation of +2 ppmv with an e-folding time of two months have been simulated. Since water vapor acts as an in-situ source of odd hydrogen in the stratosphere, the water vapor perturbations affect the gas-phase chemistry of hydrogen oxides. An additional water vapor amount of +1 ppmv results in a 5–10%  increase. Coupling processes between and / also affect the ozone destruction by other catalytic reaction cycles. The  cycle becomes 6.4% more effective, whereas the cycle is 1.6% less effective. A long-term water vapor increase does not only affect the gas-phase chemistry, but also the heterogeneous ozone chemistry in polar regions. The additional water vapor intensifies the strong denitrification of the Antarctic winter stratosphere caused by an enhanced formation of polar stratospheric clouds. Thus it further facilitates the catalytic ozone removal by the cycle. The reduction of total column ozone during Antarctic spring peaks at −3%. In contrast, heterogeneous chemistry during Arctic winter is not affected by the water vapor increase. The short-term perturbation studies show similar patterns, but because of the short perturbation time, the chemical effect on ozone is almost negligible. Finally, this study shows that 10% of the simulated long-term ozone decline in the transient model simulation can be explained by the water vapor increase, but the simulated tropical ozone decrease after volcanic eruptions is caused dynamically rather than chemically.
Measurements of N2O5, NO2, and O3 east of the San Francisco Bay
Authors: Wood E. C. , Bertram T. H. , Wooldridge P. J. , Cohen R. C.
Published: April 2010

Abstract. We report in situ measurements of N2O5, NO2, and O3 in Contra Costa County, California during January 2004. Mixing ratios of N2O5, an intermediate compound in the atmosphere's nocturnal cleansing process, ranged up to 200 pmol/mol at night. The highest N2O5 concentrations were correlated with low O3 and high NO2 concentrations. The calculated steady state lifetime for N2O5 ranged from 5 to 30 min. The total HNO3 produced by N2O5 hydrolysis over a 14 h night was comparable to ambient NO2 concentrations, and is estimated to be a factor of nine bigger than the HNO3 produced during the day.
The role of organic aerosols in homogeneous ice formation
Authors: Kärcher B. , Koop T.
Published: April 2010

Abstract. Recent field observations suggest that the fraction of organics containing aerosol particles in ice cloud particles is diminished when compared to the background aerosol prior to freezing. In this work, we use model calculations to investigate possible causes for the observed behavior. In particular, homogeneous freezing processes in cooling air parcels containing aqueous inorganic particles (represented by sulfuric acid) and organic particles (represented by pure malonic acid and mixed malonic/sulfuric acid) are studied with a detailed microphysical model. A disparate water uptake and resulting size differences that occur between organic and inorganic particles prior to freezing are identified as the most likely reason for the poor partitioning of organic aerosols into the ice phase. The differences in water uptake can be caused by changes in the relationship between solute mass fraction and water activity of the supercooled liquid phase, by modifications of the accommodation coefficient for water molecules, or by a combination thereof. The behavior of peak ice saturation ratios and total ice crystal number concentrations is examined, and the dependence of the results on cooling rate is investigated. Finally, processes are discussed that could possibly modify the homogeneous freezing behavior of organic particles.
Pole-to-pole validation of GOME WFDOAS total ozone with groundbased data
Authors: Weber M. , Lamsal L. N. , Coldewey-Egbers M. , Bramstedt K. , Burrows J. P.
Published: April 2010

Abstract. This paper summarises the validation of GOME total ozone retrieved using the weighting function differential optical absorption spectroscopy (WFDOAS) algorithm Version 1.0. This algorithm has been described in detail in a companion paper by Coldewey-Egbers et al. (2004). The WFDOAS results have been compared with selected ground-based measurements from the WOUDC (World Ozone and UV Radiation Data Centre) that collects total ozone measurements from a global network of stations covering all seasons. From the global validation excellent agreement between WFDOAS and ground data was found and on average agree to within ±1%. Very little seasonal variations in the observed differences are observed. In the polar region and at high solar zenith angles, however, a positive bias varying between 5 and 8% is found. Very few stations carry out simultaneous measurements by Brewer and Dobson spectrometers over an extended period (three years or more). Simultaneous Brewer and Dobson measurements from Hradec Kralove, Czech Republic (50.2° N, 15.8° E) and Hohenpeissenberg, Germany (47.8° N, 11.0° E) covering the period 1996–1999 have been compared with our GOME results. Agreement with Brewers are generally better than with the simultaneous Dobson measurements and this may be explained by the neglect of stratospheric (ozone) temperature correction in the standard ozone retrieval from the ground.
Radar observations of meteor trails, and their interpretation using Fresnel holography: a new tool in meteor science
Authors: Elford W. G.
Published: April 2010

Abstract. A Fresnel Transform technique has been developed at Adelaide to analyse radar meteor echoes detected in the transverse mode. The genesis for this technique was the study of the structure of the scattering ionization immediately behind the head of the trail, in order to deduce the degree of fragmentation of the ablating meteoroid. The technique has been remarkably successful in not only giving insight into the fragmentation of meteoroids, but also revealing other significant features of the trails including diffusion, lateral motion of the trail during formation due to wind drift, and phase of the scattered signal in the vicinity of the head of the trail. A serendipitous outcome of the analysis is the measurement of the speed and deceleration of the meteoroid producing the trail to a precision far exceeding that available from any other method applied to transverse scatter data. Examples of the outcomes of the technique applied to meteor echoes obtained with a 54 MHz narrow beam radar are presented.
Sources and distribution of trace species in Alpine precipitation inferred from two 60-year ice core paleorecords
Authors: Eichler A. , Schwikowski M. , Furger M. , Schotterer U. , Gäggeler H. W.
Published: April 2010

Abstract. The Alps represent the largest barrier to meridional air flow in Europe, strongly influencing the weather and hence the distribution of atmospheric trace components. Here for the first time, chemical records from two ice cores retrieved from glaciers located in the northern and southern Swiss Alps were compared in conjunction with an analysis of "weather type", in order to assess geographical and seasonal trends in the deposition of trace species and to identify source regions and transport patterns. Using a correlation analysis, investigated trace species (NH4+, NO3−, SO42−, Ca2+, Mg2+, Na+, K+, and Cl− were grouped into classes of different origin (anthropogenic, sea salt, or Saharan dust). Over the last 60 years, precipitation chemistry at both sites was dominated by NH4+, NO4−, and SO42−, all of anthropogenic origin and deposited mainly in summer by way of convective precipitation. The similarity of the SO42− profiles with historical records of SO4 emissions from France and Italy indicated these two countries as key source areas for the anthropogenic species. In contrast, sea salt and Saharan dust showed major differences in transport pattern and deposition across the Alps. Currently, the sea-salt constituents Na+, K+, and Cl− are transported to the northern site during advective westerly-wind situations, independent of Saharan dust events. At the southern site, sea salt and Saharan dust are deposited simultaneously, indicating a coupled transport active mainly in summer during south-westerly wind situations.
Rapid meridional transport of tropical airmasses to the Arctic during the major stratospheric warming in January 2003
Authors: Kleinböhl A. , Kuttippurath J. , Sinnhuber M. , Sinnhuber B. M. , Küllmann H. , Künzi K. , Notholt J.
Published: April 2010

Abstract. We present observations of unusually high values of ozone and N2O in the middle stratosphere that were observed by the airborne submillimeter radiometer ASUR in the Arctic. The observations took place in the meteorological situation of a major stratospheric warming that occurred in mid-January 2003 and was dominated by a wave 2 event. On 23 January 2003 the observed N2O and O3 mixing ratios around 69° N in the middle stratosphere reached maximum values of ~190 ppb and ~10 ppm, respectively. The similarities of these N2O profiles in a potential temperature range between 800 and 1200 K with N2O observations around 20° N on 1 March 2003 by the same instrument suggest that the observed Arctic airmasses were transported from the tropics by isentropic transport. Using a linearized ozone chemistry model along idealized trajectories at different altitudes transport times between about 3 and 7 days are estimated from the difference between the Arctic and tropical O3mixing ratios observed in this potential temperature range. PV distributions suggest that these airmasses did not stay confined in the Arctic region which makes it unlikely that this dynamical situation lead to the formation of dynamically caused pockets of low ozone.
Aerosol optical depth measurements by airborne sun photometer in SOLVE II: Comparisons to SAGE III, POAM III and airborne spectrometer measurements
Authors: Russell P. , Livingston J. , Schmid B. , Eilers J. , Kolyer R. , Redemann J. , Ramirez S. , Yee J.-H. , Swartz W. , Shetter R. , Trepte C. , Risley Jr. A. , Wenny B. , Zawodny J. , Chu W. , Pitts M. , Lumpe J. , Fromm M. , Randall C. , Hoppel K. , Bevilacqua R.
Published: April 2010

Abstract. The 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) measured solar-beam transmission on the NASA DC-8 during the Second SAGE III Ozone Loss and Validation Experiment (SOLVE II). This paper presents AATS-14 results for multiwavelength aerosol optical depth (AOD), including its spatial structure and comparisons to results from two satellite sensors and another DC-8 instrument. These are the Stratospheric Aerosol and Gas Experiment III (SAGE III), the Polar Ozone and Aerosol Measurement III (POAM III) and the Direct-beam Irradiance Airborne Spectrometer (DIAS). AATS-14 provides aerosol results at 13 wavelengths λ spanning the full range of SAGE III and POAM III aerosol wavelengths. Because most AATS measurements were made at solar zenith angles (SZA) near 90°, retrieved AODs are strongly affected by uncertainties in the relative optical airmass of the aerosols and other constituents along the refracted line of sight (LOS) between instrument and sun. To reduce dependence of the AATS-satellite comparisons on airmass, we perform the comparisons in line-of-sight (LOS) transmission and LOS optical thickness (OT) as well as in vertical OT (i.e., optical depth, OD). We also use a new airmass algorithm that validates the algorithm we previously used to within 2% for SZA<90°, and in addition provides results for SZA≥90°. For 6 DC-8 flights, 19 January–2 February 2003, AATS and DIAS results for LOS aerosol optical thickness (AOT) at λ=400 nm agree to ≤12% of the AATS value. Mean and root-mean-square (RMS) differences, (DIAS-AATS)/AATS, are –2.3% and 7.7%, respectively. For DC-8 altitudes, AATS-satellite comparisons are possible only for λ>440 nm, because of signal depletion for shorter λ on the satellite full-limb LOS. For the 4 AATS-SAGE and 4 AATS-POAM near-coincidences conducted 19–31 January 2003, AATS-satellite AOD differences were ≤0.0041 for all λ>440 nm. RMS differences were ≤0.0022 for SAGE-AATS and ≤0.0026 for POAM-AATS. RMS percentage differences in AOD ([SAGE-AATS]/AATS) were ≤33% for λ<~755 nm, but grew to 59% for 1020 nm and 66% at 1545 nm. For λ>~755 nm, AATS-POAM differences were less than AATS-SAGE differences, and RMS percentage differences in AOD ([AATS-POAM]/AATS) were ≤31% for all λ between 440 and 1020 nm. Unexplained differences that remain are associated with transmission differences, rather than differences in gas subtraction or conversion from LOS to vertical quantities. The very small stratospheric AOD values that occurred during SOLVE II added to the challenge of the comparisons, but do not explain all the differences.
An evaluation of the performance of chemistry transport models, Part 2: detailed comparison with two selected campaigns
Authors: Brunner D. , Staehelin J. , Rogers H. L. , Köhler M. O. , Pyle J. A. , Hauglustaine D. A. , Jourdain L. , Berntsen T. K. , Gauss M. , Isaksen I. S. A. , Meijer E. , van Velthoven P. , Pitari G. , Mancini E. , Grewe V. , Sausen R.
Published: April 2010

Abstract. This is the second part of a rigorous model evaluation study involving five global Chemistry-Transport and two Chemistry-Climate Models operated by different groups in Europe. Simulated trace gas fields were interpolated to the exact times and positions of the observations to account for the actual weather conditions and hence for the specific histories of the sampled air masses. In this part of the study we focus on a detailed comparison with two selected campaigns, PEM-Tropics A and SONEX, contrasting the clean environment of the tropical Pacific with the more polluted North Atlantic region. The study highlights the different strengths and weaknesses of the models in accurately simulating key processes in the UT/LS region including stratosphere-troposphere-exchange, rapid convective transport, lightning emissions, radical chemistry and ozone production. Model simulated Radon, which was used as an idealized tracer for continental influence, was occasionally much better correlated with measured CO than simulated CO pointing towards deficiencies in the used biomass burning emission fields. The abundance and variability of HOx radicals is in general well represented in the models as inferred directly from the comparison with measured OH and HO2 and indirectly from the comparison with hydrogen peroxide concentrations. Components of the NOy family such as PAN, HNO3 and NO were found to compare less favorably. Interestingly, models showing good agreement with observations in the case of PEM-Tropics A often failed in the case of SONEX and vice versa. A better description of NOx and NOy emissions, chemistry and sinks is thought to be key to future model improvements with respect to the representation of chemistry in the UT/LS region.
Observations of convective cooling in the tropical tropopause layer in AIRS data
Authors: Kim H. , Dessler A. E.
Published: April 2010

Abstract. We investigate the impact of convection on the thermal structure of the Tropical Tropopause Layer (TTL). We use temperature profiles measured by the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite, and the time evolution of local convection determined by the National Centers for Environmental Protection/Aviation Weather Center (NCEP/AWS) half-hourly infrared global geostationary composite. The observations demonstrate that the TTL is cooled by convection, in agreement with previous observations and model simulations. By using a global data set, we are able to investigate the variations in this convective cooling by season and region. The estimated cooling rate during active convection is 7.5~9 K/day. While we cannot unambiguously identify the cause of this cooling, our analysis suggests that radiative cooling is likely not an explanation.
A pseudo-Lagrangian model study of the size distribution properties over Scandinavia: transport from Aspvreten to Värriö
Authors: Tunved P. , Korhonen H. , Ström J. , Hansson H.-C. , Lehtinen K. E. J. , Kulmala M.
Published: April 2010

Abstract. The evolution of the aerosol size distribution during transport between Aspvreten (58.8° N, 17.4° E) and Värriö (67.46° N, 29.35° E) was studied using a pseudo-Lagrangian approach. Aerosol dynamic processes were studied and interpreted utilizing a state-of-the-art aerosol dynamic box model UHMA (University of Helsinki Multicomponent Aerosol model) complemented with OH, NO3, O3 and terpene chemistry. In the model simulations, the growth and formation of aerosol particles was controlled by sulphuric acid, ammonia, water and an unidentified low volatile organic compound. This organic compound was assumed to be a product of terpene oxidation with a yield of 13% in the base case conditions. Changes of aerosol size distribution properties during transport between the stations were examined in twelve clear sky cases. On average, the modelled number agreed fairly well with observations. Mass concentration was overestimated by 10%. Apart from dilution, the only removal mechanism for aerosol mass is dry deposition. A series of sensitivity tests performed revealed that the absolute magnitude of dry deposition effects on the aerosol size distribution is slow overall. Furthermore, nucleation does not leave a significant contribution to aerosol number in the selected cases. The sensitivity of the modelled size distribution to concentration of precursor gases and oxidants is, however, obvious. In order to explain observed mass increase during transport we conclude that a yield of low volatile products from oxidation of terpenes of 10–15% is required to explain observed growth rates. Coagulation is acknowledged to be highly important in modelled cases.
Simulation of denitrification and ozone loss for the Arctic winter 2002/2003
Authors: Grooß J.-U. , Günther G. , Müller R. , Konopka P. , Bausch S. , Schlager H. , Voigt C. , Volk C. M. , Toon G. C.
Published: April 2010

Abstract. We present simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the Arctic winter 2002/2003. We integrated a Lagrangian denitrification scheme into the three-dimensional version of CLaMS that calculates the growth and sedimentation of nitric acid trihydrate (NAT) particles along individual particle trajectories. From those, we derive the HNO3 downward flux resulting from different particle nucleation assumptions. The simulation results show a clear vertical redistribution of total inorganic nitrogen (NOy), with a maximum vortex average permanent NOy removal of over 5 ppb in late December between 500 and 550 K and a corresponding increase of NOy of over 2 ppb below about 450 K. The simulated vertical redistribution of NOy is compared with balloon observations by MkIV and in-situ observations from the high altitude aircraft Geophysica. Assuming a globally uniform NAT particle nucleation rate of 3.4·10−6cm−3h−1 in the model, the observed denitrification is well reproduced. In the investigated winter 2002/2003, the denitrification has only moderate impact (≤10%) on the simulated vortex average ozone loss of about 1.1 ppm near the 460 K level. At higher altitudes, above 600 K potential temperature, the simulations show significant ozone depletion through NOx-catalytic cycles due to the unusual early exposure of vortex air to sunlight.
Intercomparison of satellite retrieved aerosol optical depth over ocean during the period September 1997 to December 2000
Authors: Myhre G. , Stordal F. , Johnsrud M. , Diner D. J. , Geogdzhayev I. V. , Haywood J. M. , Holben B. , Holzer-Popp T. , Ignatov A. , Kahn R. , Kaufman Y. J. , Loeb N. , Martonchik J. , Mishchenko M. I. , Nalli N. R. , Remer L. A. , Schroedter-Homscheidt M. , Tanré D. , Torres O. , Wang M.
Published: April 2010

Abstract. Monthly mean aerosol optical depth (AOD) over ocean is compared from a total of 9 aerosol retrievals during a 40 months period. Comparisons of AOD have been made both for the entire period and sub periods. We identify regions where there is large disagreement and good agreement between the aerosol satellite retrievals. Significant differences in AOD have been identified in most of the oceanic regions. Several analyses are performed including spatial correlation between the retrievals as well as comparison with AERONET data. During the 40 months period studied there have been several major aerosol field campaigns as well as events of high aerosol content. It is studied how the aerosol retrievals compare during such circumstances. The differences found in this study are larger than found in a previous study where 5 aerosol retrievals over an 8 months period were compared. However, results in coastal regions are promising especially for aerosol retrievals from satellite instruments dedicated for aerosol research. In depth analyses explaining the differences between AOD obtained in different retrievals are clearly needed. We limit this study to identify differences and similarities and indicate possible sources that affect the quality of the retrievals. This is a necessary first step towards understanding the differences and improving the retrievals.
A case study on the formation and evolution of ice supersaturation in the vicinity of a warm conveyor belt’s outflow region
Authors: Spichtinger P. , Gierens K. , Wernli H.
Published: April 2010

Abstract. A case study is presented on the formation and evolution of an ice-supersaturated region (ISSR) that was detected by a radiosonde in NE Germany at 06:00 UTC 29 November 2000. The ISSR was situated in the vicinity of the outflow region of a warm conveyor belt associated with an intense event of cyclogenesis in the eastern North Atlantic. Using ECMWF analyses and trajectory calculations it is determined when the air parcels became supersaturated and later subsaturated again. In the case considered, the state of air parcel supersaturation can last for longer than 24 h. The ISSR was unusually thick: while the mean vertical extension of ISSRs in NE Germany is about 500 m, the one investigated here reached 3 km. The investigated ice-supersaturated region was bordered both vertically and horizontally by strongly subsaturated air. Near the path of the radiosonde the ISSR was probably cloud free, as inferred from METEOSAT infrared images. However, at other locations within the ISSR it is probable that there were cirrus clouds. Relative humidity measurements are used to correct the negative bias of the ECMWF humidity and to construct two-dimensional maps of ice supersaturation over Europe during the considered period. A systematic backward trajectory analysis for the ISSRs on these maps shows that the ISSR air masses themselves experienced only a moderate upward motion during the previous days, whereas parts of the ISSRs were located just above strongly ascending air masses from the boundary layer. This indicates qualitatively that warm conveyor belts associated with mid-latitude cyclogenesis are disturbances that can induce the formation of ISSRs in the upper troposphere. The ISSR maps also lead us to a new perception of ISSRs as large dynamic regions of supersaturated air where cirrus clouds can be embedded at some locations while there is clear air at others.
Water vapour and ozone profiles in the midlatitude upper troposphere
Authors: Vaughan G. , Cambridge C. , Dean L. , Phillips A. W.
Published: April 2010

Abstract. We present an investigation of upper tropospheric humidity profiles measured with a standard radiosonde, the Vaisala RS80-A, and a commercial frost-point hygrometer, the Snow White. Modifications to the Snow White, to enable the mirror reflectivity and Peltier cooling current to be monitored during flight, were found to be necessary to determine when the instrument was functioning correctly; a further modification to prevent hydrometeors entering the inlet was also implemented. From 23 combined flights of an ozonesonde, radiosonde and Snow White between September 2001 and July 2002, clear agreement was found between the two humidity sensors, with a mean difference of <2% in relative humidity from 2 to 10 km, and 2.2% between 10 and 13 km. This agreement required a correction to the radiosonde humidity, as described by Miloshevich et al. (2001). Using this result, the dataset of 324 ozonesonde/RS80-A profiles measured from Aberystwyth between 1991 and 2002 was examined to derive statistics for the distribution of water vapour and ozone. Supersaturation with respect to ice was frequently seen at the higher levels – 24% of the time in winter between 8 and 10 km. The fairly uniform distribution of relative humidity persisted to 120% in winter, but decreased rapidly above 100% in summer.
Nanoparticle formation by ozonolysis of inducible plant volatiles
Authors: Joutsensaari J. , Loivamäki M. , Vuorinen T. , Miettinen P. , Nerg A.-M. , Holopainen J. K. , Laaksonen A.
Published: April 2010

Abstract. We present the first laboratory experiments of aerosol formation from oxidation of volatile organic species emitted by living plants, a process which for half a century has been known to take place in the atmosphere. We have treated white cabbage crops with methyl jasmonate in order to induce the production of monoterpenes and certain less-volatile sesqui- and homoterpenes. Ozone was introduced into the growth chamber in which the crops were placed, and the subsequent aerosol formation and growth of aerosols were monitored by measuring the particle size distributions continuously during the experiments. Our observations show similar particle formation rates as in the atmosphere but much higher growth rates. The results indicate that the concentrations of nonvolatile oxidation products of plant released precursors needed to induce the nucleation are roughly an order-of-magnitude higher than their concentrations during atmospheric nucleation events. Our results therefore suggest that atmospheric nucleation events proceed via condensation of oxidized organics on pre-existing molecular clusters rather than via their homogeneous or ion-induced nucleation.
Global impact of road traffic emissions on tropospheric ozone
Authors: Matthes S. , Grewe V. , Sausen R. , Roelofs G.-J.
Published: April 2010

Abstract. Road traffic is one of the major anthropogenic emission sectors for NOx, CO and NMHCs (non-methane hydrocarbons). We applied ECHAM4/CBM, a general circulation model coupled to a chemistry module, which includes higher hydrocarbons, to investigate the global impact of road traffic emissions on the atmosphere. Improving over previous global modelling studies, which concentrated on road traffic NOx and CO-emissions only, we assess the impact of NMHC-emissions from road traffic. It is revealed that NMHC-emissions from road traffic play a key role for the impact on ozone. They are responsible for (indirect) long-range transport of NOx from road traffic via the formation of PAN, which is not found in a simulation without NMHC emissions from road traffic. Long-range transport of NMHC-induced PAN impacts on the ozone distribution in northern hemisphere regions far away from the sources, especially in Arctic and remote maritime regions. There, during subsidence, PAN acts as a source for NOx, caused by thermal decay. Hence, ozone is produced. In July total road traffic emissions (NOx, CO and NMHCs) contribute to the zonally averaged ozone distribution by more than 12% near the surface in the northern hemisphere midlatitudes and arctic latitudes. In January road traffic emissions contribute near the surface in northern and southern extratropics more than 8%. Sensitivity studies for regional emission show that effective transport of road traffic emissions occurs mainly in the free troposphere. In tropical latitudes of America up to an altitude of 200 hPa, global road traffic emissions contribute about 4% to the ozone concentration.
Spectroscopic evidence for β-NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds
Authors: Höpfner M. , Luo B. P. , Massoli P. , Cairo F. , Spang R. , Snels M. , Di Donfrancesco G. , Stiller G. , von Clarmann T. , Fischer H. , Biermann U.
Published: April 2010

Abstract. We have analyzed mid-infrared limb-emission measurements of polar stratospheric clouds (PSCs) by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) during the Antarctic winter 2003 with respect to PSC composition. Coincident lidar observations from McMurdo were used for comparison with PSC types 1a, 1b and 2. By application of new refractive index data we could prove that a spectral signature at 820 cm−1 as observed by MIPAS near to the observation of a type 1a PSC is due to a composition of β-NAT. MIPAS infrared spectra collocated with Lidar observations of Type 1b and Type 2 PSCs could only be reproduced by assuming a composition of supercooled ternary H2SO4/HNO3/H2O solution (STS) and of ice, respectively. Particle radius and number density profiles derived from MIPAS were generally consistent with the lidar observations. Only in the case of ice clouds, PSC volumes are underestimated due to large cloud optical thickness in the limb-direction. A comparison of MIPAS cloud composition and lidar PSC-type determination based on all available MIPAS-lidar coincident measurements revealed good agreement between PSC-types 1a, 1b and 2, and NAT, STS and ice, respectively. We could not find any spectroscopic evidence for the presence of nitric acid dihydrate (NAD) from any MIPAS observation of PSCs over Antarctica in 2003.