bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
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.
2-D reconstruction of atmospheric concentration peaks from horizontal long path DOAS tomographic measurements: parametrisation and geometry within a discrete approach
Authors: Hartl A. , Song B. C. , Pundt I. 
Published: April 2010

Abstract. In this study, we theoretically investigate the reconstruction of 2-D cross sections through Gaussian concentration distributions, e.g. emission plumes, from long path DOAS measurements along a limited number of light paths. This is done systematically with respect to the extension of the up to four peaks and for six different measurement setups with 2–4 telescopes and 36 light paths each. We distinguish between cases with and without additional background concentrations. Our approach parametrises the unknown distribution by local piecewise constant or linear functions on a regular grid and solves the resulting discrete, linear system by a least squares minimum norm principle. We show that the linear parametrisation not only allows better representation of the distributions in terms of discretisation errors, but also better inversion of the system. We calculate area integrals of the concentration field (i.e. total emissions rates for non-vanishing perpendicular wind speed components) and show that reconstruction errors and reconstructed area integrals within the peaks for narrow distributions crucially depend on the resolution of the reconstruction grid. A recently suggested grid translation method for the piecewise constant basis functions, combining reconstructions from several shifted grids, is modified for the linear basis functions and proven to reduce overall reconstruction errors, but not the uncertainty of concentration integrals. We suggest a procedure to subtract additional background concentration fields before inversion. We find large differences in reconstruction quality between the geometries and conclude that, in general, for a constant number of light paths increasing the number of telescopes leads to better reconstruction results. It appears that geometries that give better results for negligible measurement errors and parts of the geometry that are better resolved are also less sensitive to increasing measurement errors.
Commentary on ''Measurements of ice supersaturations exceeding 100% at the cold tropical tropopause'' by E. Jensen et al.
Authors: Murphy D. M. 
Published: April 2010

Abstract. The paper by Jensen et al. (2005) provides an excellent use of a microphysical model to examine the logical consequences of high saturation ratios indicated by measurements during a high altitude flight of the NASA WB-57F. I would like to comment on a turn made by the aircraft that makes this particular event harder to interpret.
Characterization of air ions in boreal forest air during BIOFOR III campaign
Authors: Hõrrak U. , Aalto P. P. , Salm J. , Mäkelä J. M. , Laakso L. , Laakso L. , Kulmala M. 
Published: April 2010

Abstract. The behavior of the concentration of positive small (or cluster) air ions and naturally charged nanometer aerosol particles (aerosol ions) has been studied on the basis of measurements carried out in a boreal forest at the Hyytiälä SMEAR station, Finland, during the BIOFOR III campaign in spring 1999. Statistical characteristics of the concentrations of cluster ions, two classes of aerosol ions of the sizes of 2.5–8 nm and 8–ca 20 nm and the quantities that determine the balance of small ions in the atmosphere have been given for the nucleation event days and non-event days. The dependence of small ion concentration on the ion loss (sink) due to aerosol particles was investigated applying a model of bipolar diffusion charging of particles by small ions. The small ion concentration and the ion sink were closely correlated (correlation coefficient 87%) when the fog events and the hours of high relative humidity (above 97%), as well as nocturnal calms and weak wind (wind speed<0.6 m s-1 had been excluded. In the case of nucleation burst events, variations in the concentration of small positive ions were in accordance with the changes caused by the ion sink due to aerosols; no clear indication of positive ion depletion by ion-induced nucleation was found. The estimated average ionization rate of air at the Hyytiälä station in early spring, when the ground was partly covered with snow, was about 4.8 ion pairs cm-3 s-1. The study of the charging state of nanometer aerosol particles (2.5–8 nm) revealed a strong correlation (correlation coefficient 88%) between the concentrations of particles and their charged fraction (positive air ions) during nucleation bursts. The estimated charged fraction of particles, which varied from 3% to 6% considering various nucleation event days, confirms that these particles are almost quasi-steady state charged. Also the particles and air ions in the size range of 8–ca 20 nm showed a good qualitative consistency; the correlation coefficient was 92%.
Airborne measurements of trace gas and aerosol particle emissions from biomass burning in Amazonia
Authors: Guyon P. , Frank G. , Welling M. , Chand D. , Artaxo P. , Rizzo L. , Nishioka G. , Kolle O. , Fritsch H. , Silva Dias M. A. F. , Gatti L. V. , Cordova M. , Andreae M. O. 
Published: April 2010

Abstract. As part of the LBA-SMOCC (Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall, and Climate) 2002 campaign, we studied the emission of carbon monoxide (CO), carbon dioxide (CO2), and aerosol particles from Amazonian deforestation fires using an instrumented aircraft. Emission ratios for aerosol number (CN) relative to CO (ERCN/CO) fell in the range 14–32 cm-3 ppb-1 for most of the time, in agreement with values usually found from tropical savanna fires. The number of particles emitted per amount biomass burned was found to be dependant on the fire condition (combustion efficiency). Variability in the ERCN/CO between fires was similar to the variability caused by variations in combustion behavior within each individual fire. This was confirmed by observations of CO-to-CO2 emission ratios (ERCO/CO2), which stretched across the same wide range of values for individual fires as for all the fires observed during the sampling campaign, indicating that flaming and smoldering phases are present simultaneously in deforestation fires. Emission factors (EF) for CO and aerosol particles were computed and a correction was applied for the residual smoldering combustion (RSC) fraction of emissions that are not sampled by the aircraft. The correction, previously unpublished for tropical deforestation fires, suggested an EF about one and a half to twice as large for these species. Vertical transport of biomass-burning plumes from the boundary layer (BL) to the cloud detrainment layer (CDL) and the free troposphere (FT) was found to be a very common phenomenon. We observed a 20% loss in particle number as a result of this vertical transport and subsequent cloud processing, attributable to in-cloud coagulation. This small loss fraction suggests that this mode of transport is very efficient in terms of particle numbers and occurs mostly via non-precipitating clouds. The detrained aerosol particles released in the CDL and FT were larger due to coagulation and secondary growth, and therefore more efficient at scattering radiation and nucleating cloud droplets than the fresh particles. This process may have significant atmospheric implications on a regional and larger scale.
Morphological, chemical and optical absorbing characterization of aerosols in the urban atmosphere of Valladolid
Authors: Mogo S. , Cachorro V. E. , de Frutos A. M. 
Published: April 2010

Abstract. Aerosol samples were collected from the Valladolid (Spain) atmosphere during 2003–2004 winter using a Dekati PM10 cascade impactor which allows to discriminate four level of particle sizes: greater than 10 µm, between 10 and 2.5, from 2.5 to 1 and less than 1 µm. The size and shape of the aerosol deposits were analyzed by means of individual particles through scanning electron microscope (SEM) technique. Additionally an energy dispersive X-ray analysis (EDX) was performed enabling elemental analysis of a large number of individual particles in a relatively short time. We present a classification in size, shape and composition of the major particulate species present in the Valladolid urban atmosphere. The aerosol concentration is very variable during winter, ranging from 39.86&amp;nbspµg·m−3 to 184.88 µg·m−3 with coarse particle as dominant fraction. Emphasize was given to fine particles, behind 1 µm, for which the visible (from 400 nm to 650 nm) light absorption coefficients were measured using the integrating plate technique. We have made some enhancements relative to the illumination system in the well known integrating plate method, for the absorption coefficients determination. The absorption coefficient ranges from 7.33×10−6 m−1 to 1.01×10−4 m−1 for the 550 nm wavelength. Its visible spectrum decreases with wavelength with greater slope for greater σ values.