bluuebunny/crossref_metadata_2025_split huggingface dataset:
Retrieval and validation of ozone columns derived from measurements of SCIAMACHY on Envisat
Authors: Eskes H. J. , van der A R. J. , Brinksma E. J. , Veefkind J. P. , de Haan J. F. , Valks P. J. M. 
Published: April 2010

Abstract. This paper describes a new ozone column retrieval algorithm and its application to SCIAMACHY measurements. The TOSOMI algorithm is based on the Differential Optical Absorption Spectroscopy (DOAS) technique and implements several improvements over older algorithms. These improvements include aspects like (i) the explicit treatment of rotational Raman scattering, (ii) an improved air-mass factor formulation which is based on a simulation of the reflectivity spectrum and a subsequent DOAS fit of this simulated spectrum, (iii) the use of an improved ozone climatology and a column dependent air-mass factor, (iv) the use of daily varying ECMWF temperature profile analyses. The results of three validation exercises are reported. The TOSOMI columns are compared with an extensive set of ground-based observations (Brewer, Dobson) for the years 2003 and 2004. Secondly, a direct comparison for January–June 2003 with two new GOME retrievals, GDP Version 4 and TOGOMI, is presented. Third, data assimilation is used to study the dependence of the TOSOMI columns with retrieval parameters such as the viewing angle, cloud fraction and geographical location. These comparisons show a good consistency on the percent level between the GOME and SCIAMACHY algorithms. The present TOSOMI implementation (v0.32) shows an offset of about −1.5% with respect to ground-based observations and the GOME retrievals.
Observations and model calculations of trace gas scavenging in a dense Saharan dust plume during MINATROC
Authors: de Reus M. , Fischer H. , Sander R. , Gros V. , Kormann R. , Salisbury G. , Van Dingenen R. , Williams J. , Zöllner M. , Lelieveld J. 
Published: April 2010

Abstract. An intensive field measurement campaign was performed in July/August 2002 at the Global Atmospheric Watch station Izaña on Tenerife to study the interaction of mineral dust aerosol and tropospheric chemistry (MINATROC). A dense Saharan dust plume, with aerosol masses exceeding 500 µg m-3, persisted for three days. During this dust event strongly reduced mixing ratios of ROx (HO2, CH3O2 and higher organic peroxy radicals), H2O2, NOx (NO and NO2) and O3 were observed. A chemistry boxmodel, constrained by the measurements, has been used to study gas phase and heterogeneous chemistry. It appeared to be difficult to reproduce the observed HCHO mixing ratios with the model, possibly related to the representation of precursor gas concentrations or the absence of dry deposition. The model calculations indicate that the reduced H2O2 mixing ratios in the dust plume can be explained by including the heterogeneous removal reaction of HO2 with an uptake coefficient of 0.2, or by assuming heterogeneous removal of H2O2 with an accommodation coefficient of 3×10-4. However, these heterogeneous reactions cannot explain the low ROx mixing ratios observed during the dust event. Whereas a mean daytime net ozone production rate (NOP) of 1.06 ppbv/hr occurred throughout the campaign, the reduced ROx and NOx mixing ratios in the Saharan dust plume contributed to a reduced NOP of 0.14–0.32 ppbv/hr, which likely explains the relatively low ozone mixing ratios observed during this event.
Aerosol formation over the Boreal forest in Hyytiälä, Finland: monthly frequency and annual cycles – the roles of air mass characteristics and synoptic scale meteorology
Authors: Nilsson E. D. , Kulmala M. 
Published: April 2010

Abstract. New atmospheric particles with diameters of 3–10 nm and their subsequent growth to cloud condensation nucleus have been observed at various places in the European boundary layer. These events have been observed simultaneously within wide geographical areas (over 1000 km) in connection to specific weather systems, the cold air behind cyclones. Here we show that atmospheric aerosol formation (i.e. nucleation and initial growth) is favoured by the outbreak of cold Arctic air over northern Europe. Aerosol formation was about twice as common in Arctic air as in sub-Polar air, and even more so compared to other air masses. The most important general factor favouring aerosol formation in Arctic air and marine air was weaker competing condensational sink (CS) for the precursor gases (less pre-existing aerosols), while high CS prevented aerosol formation in heated sub-Polar air and mid-latitude air. High SO2 levels favoured nucleation in continental air and high UV-B radiation in sub-tropical air. The critical factor that determined if aerosol formation would start on a day with Arctic air was the UV-B radiation. The same applied to sub-Polar air and continental air, while increased SO2 concentration could trigger formation in heated sub-Polar and mid-latitude air, and reduced CS could cause formation in mid-latitude, marine or mixed/transient air. We speculate that strong emissions of volatile organic compounds from the Boreal forest and strong boundary layer dynamics may have caused aerosol formation in sub-Polar air masses and air in transition from a marine to a continental character. The monthly frequency of Arctic air masses and the probability for photo-chemically driven aerosol formation explains the observed annual cycle in monthly particle formation frequency as well as much of the inter annual variability. The same cyclones that transport cold, clean air from the Arctic to Europe will also transport warm polluted air in the other direction, which help cause the Arctic Haze phenomena. The cyclones have a key role for the atmospheric aerosol life cycle in mid to high latitudes. Due to the observed growth to the size of CCN in one to two days, there is a potential feed back from the effects on the CCN population and cloud albedo even within the same weather system, but also on the climatic time scale.
Free radical modelling studies during the UK TORCH Campaign in summer 2003
Authors: Emmerson K. M. , Carslaw N. , Carslaw D. C. , Lee J. D. , McFiggans G. , Bloss W. , Gravestock T. , Heard D. E. , Hopkins J. , Ingham T. , Pilling M. J. , Smith S. C. , Jacob M. J. , Monks P. S. 
Published: April 2010

Abstract. The Tropospheric ORganic CHemistry experiment (TORCH) took place during the heatwave of summer 2003 at Writtle College, a site 2 miles west of Chelmsford in Essex and 25 miles north east of London. The experiment was one of the most highly instrumented to date. A combination of a large number of days of simultaneous, collocated measurements, a consequent wealth of model constraints and a highly detailed chemical mechanism, allowed the atmospheric chemistry of this site to be studied in detail. The concentrations of the hydroxyl radical, the hydroperoxy radical and the sum of peroxy radicals, were measured between 25 July and 31 August using laser-induced fluorescence at low pressure and the peroxy radical chemical amplifier techniques. The concentrations of the radical species were predicted using a zero-dimensional box model based on the Master Chemical Mechanism version 3.1, which was constrained with the observed concentrations of relatively long-lived species. The model included a detailed parameterisation to account for heterogeneous loss of hydroperoxy radicals onto aerosol particles. Quantile-quantile plots were used to assess the model performance in respect of the measured radical concentrations. On average, measured hydroxyl radical concentrations were over-predicted by 24%. Modelled and measured hydroperoxy radical concentrations agreed very well, with the model over-predicting on average by only 7%. The sum of peroxy radicals was under-predicted when compared with the respective measurements by 22%. OH initiation was dominated by the reactions of excited oxygen atoms with water, nitrous acid photolysis and the ozone reaction with alkene species. Photolysis of aldehyde species was the main initiation route for HO2 and RO2. Termination, under all conditions, primarily involved reactions with NOx for OH and heterogeneous chemistry on aerosol surfaces for HO2. The OH chain length varied between 2 and 8 cycles, the longer chain lengths occurring before and after the most polluted part of the campaign. Peak local ozone production of 17 ppb hr−1 occurred on 3 and 5 August, signifying the importance of local chemical processes to ozone production on these days. On the whole, agreement between model and measured radicals is good, giving confidence that our understanding of atmospheres influenced by nearby urban sources is adequate.
Investigation of how observed methane concentrations in Ny-Ålesund are influenced by atmospheric flow patterns
Authors: Pedersen I. T. , Holmén K. J. 
Published: April 2010

Abstract. Long-range atmospheric transport to Svalbard has been studied with a compilation of 4 years of daily trajectories to determine how the atmospheric flow patterns influence the observed methane (CH4) at Mt. Zeppelin station (475 m.a.s.l.) in Ny-Ålesund (78&amp;deg54' N, 11°53' E). The flow patterns were determined through cluster analysis of 5-day back-trajectories arriving at Ny-Ålesund twice a day (00:00 and 12:00 UTC) for the period 2000–2003. Eight cluster patterns were obtained and used in the analysis of the continuous methane measurements at Mt. Zeppelin station. The analysis shows a shift in frequencies eastward into the Arctic compared to identical studies of transport for 1992–2001. Higher concentrations of methane are mainly seen in clusters with transport from Europe and Russia in contrast to air following transport pathways within the Arctic Basin. The vertical motion of the trajectories has been investigated and shows that it has an effect on the methane concentration at the Mt. Zeppelin station. This is consistent with previous similar studies of CO2 and of other anthropogenic species. Seasonal variation in trajectory frequency can be seen, like for instance more trajectories from Europe and Siberia during winter, and short trajectories from the Arctic region in summer. The identified seasonal and indications of decadal shifts in transport pathways translate into shifts in source areas sampled by a single station. To determine shifts in regional source (and sink) strengths it is necessary to correct for transport pathway shifts when interpreting time series data.
The effect of sensor resolution on the number of cloud-free observations from space
Authors: Krijger J. M. , van Weele M. , Aben I. , Frey R. 
Published: April 2010

Abstract. Air quality and surface emission inversions are likely to be focal points for future satellite missions on atmospheric composition. Most important for these applications is sensitivity to the atmospheric composition in the lowest few kilometers of the troposphere. Reduced sensitivity by clouds needs to be minimized. In this study we have quantified the increase in number of useful footprints, i.e. footprints which are sufficient cloud-free, as a function of sensor resolution (footprint area). High resolution (1 km×1 km) MODIS TERRA cloud mask observations are aggregated to lower resolutions. Statistics for different thresholds on cloudiness are applied. For each month in 2004 two days of MODIS data are analyzed. Globally the fraction of cloud-free observations drops from 16% at 100 km2 resolution to only 3% at 10 000 km2 if not a single MODIS observation within a footprint is allowed to be cloudy. If up to 5% or 20% of a footprint is allowed to be cloudy, the fraction of cloud-free observations is 9% or 17%, respectively, at 10 000 km2 resolution. The probability of finding cloud-free observations for different sensor resolutions is also quantified as a function of geolocation and season, showing examples over Europe and northern South America.
Photochemical modelling in the Po basin with focus on formaldehyde and ozone
Authors: Liu L. , Flatøy F. , Ordóñez C. , Braathen G. O. , Hak C. , Junkermann W. , Andreani-Aksoyoglu S. , Mellqvist J. , Galle B. , Prévôt A. S. H. , Isaksen I. S. A. 
Published: April 2010

Abstract. As part of the EU project FORMAT (Formaldehyde as a Tracer of Oxidation in the Troposphere), a field campaign was carried out in the vicinity of Milan during the summer of 2002. Results from a 3-D regional chemical transport model (NILU RCTM) were used to interpret the observations focusing primarily on HCHO and ozone. The performance of the model was assessed by comparing model results with ground based and aircraft measurements. The model results show good agreement with surface measurements, and the model is able to reproduce the photochemical episodes during fair weather days. The comparison indicates that the model can represent well the HCHO concentrations as well as their temporal and spatial variability. The relationship between HCHO and (O3×H2O) was used to validate the model ability to predict the HCHO concentrations. Further analysis revealed the importance of the representativity of different instruments: in-situ concentrations might be locally enhanced by emissions, while long path measurements over a forest can be influenced by rapid formation of HCHO from isoprene. The model is able to capture the plume from the city of Milan and the modelled levels agree generally well with the aircraft measurements, although the wind fields used in the model can lead to a displacement of the ozone plume. During the campaign period, O3 levels were seldom higher than 80 ppbv, the peak surface ozone maxima reached 90 ppbv. Those relatively low values can be explained by low emissions during the August vacation and unstable weather conditions in this period. The modelled ΔO3/ΔNOz slope at Alzate of 5.1 agrees well with the measured slope of 4.9.
Direct measurement of particle formation and growth from the oxidation of biogenic emissions
Authors: VanReken T. M. , Greenberg J. P. , Harley P. C. , Guenther A. B. , Smith J. N. 
Published: April 2010

Abstract. A new facility has been developed to investigate the formation of new particles from the oxidation of volatile organic compounds emitted from vegetation. The facility consists of a biogenic emissions enclosure, an aerosol growth chamber, and the associated instrumentation. Using the facility, new particle formation events have been induced through the reaction of ozone with three different precursor gas mixtures: an α-pinene test mixture and the emissions of Holm oak (Quercus ilex) and loblolly pine (Pinus taeda). The results demonstrate the variability between species in their potential to form new aerosol products. The emissions of Q. ilex resulted in fewer particles than did α-pinene, although the concentration of monoterpenes was roughly equal in both experiments before the addition of ozone. Conversely, the oxidation of P. taeda emissions led to the formation of more particles than either of the other two gas mixtures, despite a lower initial terpenoid concentration. These variations can be attributed to differences in the speciation of the vegetative emissions with respect to the α-pinene mixture and to each other. Specifically, the presence of β-pinene and other slower-reacting monoterpenes inhibited particle formation in the Q. ilex experiment, while the presence of sesquiterpenes, including β-caryophyllene, in the emissions of P. taeda were the likely cause of the more intense particle formation events observed during that experiment.
Stratospheric variability and trends in IPCC model simulations
Authors: Cordero E. C. , de F. Forster P. M. 
Published: April 2010

Abstract. Atmosphere and Ocean General Circulation Model (AOGCM) experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report are analyzed using both 20th and 21st century model output to better understand model variability and assess the importance of various forcing mechanisms on stratospheric trends. While models represent the climatology of the stratosphere reasonably well in comparison with NCEP reanalysis, there are biases and large variability among models. In general, AOGCMs are cooler than NCEP throughout the stratosphere, with the largest differences in the tropics. Around half the AOGCMs have a top level beneath ~2 hPa and show a significant cold bias in their upper levels (~10 hPa) compared to NCEP, suggesting that these models may have compromised simulations near 10 hPa due to a low model top or insufficient stratospheric levels. In the lower stratosphere (50 hPa), the temperature variability associated with large volcanic eruptions is either absent (in about half of the models) or the warming is overestimated in the models that do include volcanic aerosols. There is general agreement on the vertical structure of temperature trends over the last few decades, differences between models are explained by the inclusion of different forcing mechanisms, such as stratospheric ozone depletion and volcanic aerosols. However, even when human and natural forcing agents are included in the simulations, significant differences remain between observations and model trends, particularly in the upper tropical troposphere (200 hPa–100 hPa), where, since 1979, models show a warming trend and the observations a cooling trend.
New Standards for the Validation of EMC Test Sites particularly above 1 GHz
Authors: Battermann S. , Trautnitz F. W. , Garbe H. 
Published: April 2010

Abstract. Standards for the validation of alternative test sites with conducting groundplane exist for the frequency range 30-1000 MHz since the end of the eighties. Recently the procedure for fully anechoic rooms (FAR) has been included in CISPR 16 after more than 10 years intensive discussion in standards committees (CENELEC, 2002; CISPR, 2004). But there are no standards available for the validation of alternative test sites above 1 GHz. The responsible working group (WG1) in CISPR/A has drawn up the 7th common draft (CD). A CDV will be published in spring 2005. The German standards committee VDE AK 767.4.1 participates in the drafting of the standard. All suggested measurement procedures proposed in the last CDs have been investigated by measurements and theoretical analysis. This contribution describes the basic ideas and problems of the validation procedure of the test site. Furthermore measurement results and numerical calculations will be presented especially for the use of omni-directional antennas.
Optimally Accurate Second-Order Time-Domain Finite-Difference Scheme for Acoustic, Electromagnetic, and Elastic Wave Modeling
Authors: Bommaraju C. , Marklein R. , Chinta P. K. 
Published: April 2010

Abstract. Numerical methods are extremely useful in solving real-life problems with complex materials and geometries. However, numerical methods in the time domain suffer from artificial numerical dispersion. Standard numerical techniques which are second-order in space and time, like the conventional Finite Difference 3-point (FD3) method, Finite-Difference Time-Domain (FDTD) method, and Finite Integration Technique (FIT) provide estimates of the error of discretized numerical operators rather than the error of the numerical solutions computed using these operators. Here optimally accurate time-domain FD operators which are second-order in time as well as in space are derived. Optimal accuracy means the greatest attainable accuracy for a particular type of scheme, e.g., second-order FD, for some particular grid spacing. The modified operators lead to an implicit scheme. Using the first order Born approximation, this implicit scheme is transformed into a two step explicit scheme, namely predictor-corrector scheme. The stability condition (maximum time step for a given spatial grid interval) for the various modified schemes is roughly equal to that for the corresponding conventional scheme. The modified FD scheme (FDM) attains reduction of numerical dispersion almost by a factor of 40 in 1-D case, compared to the FD3, FDTD, and FIT. The CPU time for the FDM scheme is twice of that required by the FD3 method. The simulated synthetic data for a 2-D P-SV (elastodynamics) problem computed using the modified scheme are 30 times more accurate than synthetics computed using a conventional scheme, at a cost of only 3.5 times as much CPU time. The FDM is of particular interest in the modeling of large scale (spatial dimension is more or equal to one thousand wave lengths or observation time interval is very high compared to reference time step) wave propagation and scattering problems, for instance, in ultrasonic antenna and synthetic scattering data modeling for Non-Destructive Testing (NDT) applications, where other standard numerical methods fail due to numerical dispersion effects. The possibility of extending this method to staggered grid approach is also discussed. The numerical FD3, FDTD, FIT, and FDM results are compared against analytical solutions.
Microbial colonization and alteration of basaltic glass
Authors: Einen J. , Kruber C. , Øvreås L. , Thorseth I. H. , Torsvik T. 
Published: April 2010

Abstract. Microorganisms have been reported to be associated with the alteration of the glassy margin of seafloor pillow basalts (Thorseth et al., 2001, 2003; Lysnes et al., 2004). The amount of iron and other biological important elements present in basalts and the vast abundance of basaltic glass in the earth's crust, make glass alteration an important process in global element cycling. To gain further insight into microbial communities associated with glass alteration, five microcosm experiments mimicking seafloor conditions were inoculated with seafloor basalt and incubated for one year. Mineral precipitations, microbial attachment to the glass and glass alteration were visualized by scanning electron microscopy (SEM), and the bacterial community composition was fingerprinted by PCR and denaturing gradient gel electrophoresis (DGGE) in combination with sequencing. SEM analysis revealed a microbial community with low morphological diversity of mainly biofilm associated and prosthecate microorganisms. Approximately 30 nm thick alteration rims developed on the glass in all microcosms after one year of incubation; this however was also seen in non inoculated controls. Calcium carbonate precipitates showed parallel, columnar and filamentous crystallization habits in the microcosms as well as in the sterile controls. DGGE analysis showed an alteration in bacterial community profiles in the five different microcosms, as a response to the different energy and redox regimes and time. In all microcosms a reduction in number of DGGE bands, in combination with an increase in cell abundance were recorded during the experiment. Sequence analysis showed that the microcosms were dominated by four groups of organisms with phylogenetic affiliation to four taxa: The Rhodospirillaceae, a family containing phototrophic marine organisms, in which some members are capable of heterotrophic growth in darkness and N2 fixation; the family Hyphomicrobiaceae, a group of prosthecate oligotrophic organisms; the genus Rhizobium, N2 fixating heterotrophs; and the genus Sphingomonas, which are known as bio-film producing oligotrophs. Although no bioalteration of glass could be confirmed from our experiments, oligotrophic surface adhering bacteria such as the Sphingomonas sp. and Hyphomicrobium sp. may nevertheless be important for bioalteration in nature, due to their firm attachment to glass surfaces, and their potential for biofilm production.