bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of optical properties of atmospheric aerosols in Northern Finland
Authors: Aaltonen V. , Lihavainen H. , Kerminen V.-M. , Komppula M. , Hatakka J. , Eneroth K. , Kulmala M. , Viisanen Y. 
Published: April 2010

Abstract. Three years of continuous measurements of aerosol optical properties and simultaneous aerosol number size distribution measurements at Pallas GAW station, a remote subarctic site in the northern border of the boreal forest zone, have been analysed. The scattering coefficient at 550 nm varied from 0.2 to 94.4 Mm−1 with an average of 7.1±8.6 Mm−1. Both the scattering and backscattering coefficients had a clear seasonal cycle with an autumn minimum and a 4–5 times higher summer maximum. The scattering was dominated by submicron aerosols and especially so during late summer and autumn. The Ångström exponent had a clear seasonal pattern with maximum values in late summer and minimum values during wintertime. The highest hemispheric backscattering fraction values were observed in autumn. To analyse the influence of air mass origin on the aerosol optical properties a trajectory climatology was applied to the Pallas aerosol data. The most polluted trajectory patterns represented air masses from the Kola Peninsula, Scandinavia and Russia as well as long-range transport from Britain and Eastern Europe. These air masses had the largest average scattering and backscattering coefficients for all seasons. Higher than average values of the Ångström exponent were also observed in connection with transport from these areas.
Impact of the regional climate and substance properties on the fate and atmospheric long-range transport of persistent organic pollutants - examples of DDT and γ-HCH
Authors: Semeena V. S. , Feichter J. , Lammel G. 
Published: April 2010

Abstract. A global multicompartment model which is based on a 3-D atmospheric general circulation model (ECHAM5) coupled to 2-D soil, vegetation and sea surface mixed layer reservoirs, is used to simulate the atmospheric transports and total environmental fate of dichlorodiphenyltrichloroethane (DDT) and γ-hexachlorocyclohexane (γ-HCH, lindane). Emissions into the model world reflect the substance's agricultural usage in 1980 and 1990 and same amounts in sequential years are applied. Four scenarios of DDT usage and atmospheric decay and one scenario of γ-HCH are studied over a decade. The global environment is predicted to be contaminated by the substances within ca. 2a (years). DDT reaches quasi-steady state within 3-4a in the atmosphere and vegetation compartments, ca. 6a in the sea surface mixed layer and near to or slightly more than 10a in soil. Lindane reaches quasi-steady state in the atmosphere and vegetation within 2a, in soils within 8 years and near to or slightly more than 10a and in the sea surface mixed layer. The substances' differences in environmental behaviour translate into differences in the compartmental distribution and total environmental residence time, τoverall. τoverall≈0.8a for γ-HCH's and ≈1.0-1.3 a for the various DDT scenarios. Both substances' distributions are predicted to migrate in northerly direction, 5-12° for DDT and 6.7° for lindane between the first and the tenth year in the environment. Cycling in various receptor regions is a complex superposition of influences of regional climate, advection, and the substance's physico-chemical properties. As a result of these processes the model simulations show that remote boreal regions are not necessarily less contaminated than tropical receptor regions. Although the atmosphere accounts for only 1% of the total contaminant burden, transport and transformation in the atmosphere is key for the distribution in other compartments. Hence, besides the physico-chemical properties of pollutants the location of application (entry) affects persistence and accumulation emphasizing the need for georeferenced exposure models.
The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes
Authors: Lübken F.-J. , Strelnikov B. , Rapp M. , Singer W. , Latteck R. , Brattli A. , Hoppe U.-P. , Friedrich M. 
Published: April 2010

Abstract. In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N) into strong VHF radar echoes called "Polar Mesosphere Winter Echoes" (PMWE). The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE occur much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively). Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km): viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the radar backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar proton events. We have studied the sensitivity of the radar echo strength on various parameters, most important electron number density and turbulence intensity. Our observational and theoretical considerations do not provide any evidence that charged aerosol particles are needed to explain PMWE, in contrast to the summer echoes which owe their existence to charged ice particles.
Characterization of the organic composition of aerosols from Rondônia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds
Authors: Decesari S. , Fuzzi S. , Facchini M. C. , Mircea M. , Emblico L. , Cavalli F. , Maenhaut W. , Chi X. , Schkolnik G. , Falkovich A. , Rudich Y. , Claeys M. , Pashynska V. , Vas G. , Kourtchev I. , Vermeylen R. , Hoffer A. , Andreae M. O. , Tagliavini E. , Moretti F. , Artaxo P. 
Published: April 2010

Abstract. The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of state-of-the-art analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6–8% of TC (9–11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Polyhydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50–90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a small extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.
Atmospheric HULIS: How humic-like are they? A comprehensive and critical review
Authors: Graber E. R. , Rudich Y. 
Published: April 2010

Abstract. A class of organic molecules extracted from atmospheric aerosol particles and isolated from fog and cloud water has been termed HUmic-LIke Substances (HULIS) due to a certain resemblance to terrestrial and aquatic humic and fulvic acids. In light of the interest that this class of atmospheric compounds currently attracts, we comprehensively review HULIS properties, as well as laboratory and field investigations concerning their formation and characterization in atmospheric samples. While sharing some important features such as polyacidic nature, accumulating evidence suggests that atmospheric HULIS differ substantially from terrestrial and aquatic humic substances. Major differences between HULIS and humic substances, including smaller average molecular weight, lower aromatic moiety content, greater surface activity, better droplet activation ability, as well as others, are highlighted. Several alternatives are proposed that may explain such differences: (1) the possibility that mono- and di-carboxylic acids and mineral acids abundant in the atmosphere prevent the formation of large humic "supramolecular associations"; (2) that large humic macromolecules are destroyed in the atmosphere by UV radiation, O3, and OH- radicals; (3) that "HULIS" actually consists of a complex, unresolved mixture of relatively small molecules rather than macromolecular entities; and (4) that HULIS formed via abiotic and short-lived oxidative reaction pathways differ substantially from humic substances formed over long time periods via biologically-mediated reactions. It should also be recalled that the vast majority of studies of HULIS relate to the water soluble fraction, which would include only the fulvic acid fraction of humic substances, and exclude the humic acid (base-soluble) and humin (insoluble) fractions of humic substances. A significant effort towards adopting standard extraction and characterization methods is required to develop a better and meaningful comparison between different HULIS samples.
Operational mapping of atmospheric nitrogen deposition to the Baltic Sea
Authors: Hertel O. , Ambelas Skjøth C. , Brandt J. , Christensen J. H. , Frohn L. M. , Frydendall J. 
Published: April 2010

Abstract. A new model system for mapping and forecasting nitrogen deposition to the Baltic Sea has been developed. The system is based on the Lagrangian variable scale transport-chemistry model ACDEP (Atmospheric Chemistry and Deposition model), and aims at delivering deposition estimates to be used as input to marine ecosystem models. The system is tested by comparison of model results to measurements from monitoring stations around the Baltic Sea. The comparison shows that observed annual mean ambient air concentrations and wet depositions are well reproduced by the model. Diurnal mean concentrations of NHx (sum of NH3 and NH4) and NO2 are fairly well reproduced, whereas concentrations of total nitrate (sum of HNO3 and NO3−) are somewhat overestimated by the model. Wet depositions of nitrate and ammonia are fairly well described for annual mean values, whereas the discrepancy is high for the monthly mean values and the wet depositions are rather poorly described concerning the diurnal mean values. The model calculations show that the atmospheric nitrogen deposition has a pronounced south – north gradient with depositions in the range about 1.0 tonnes N km−2 in south and 0.2 tonnes N km−2 in north. The model results show that in 2000 the maximum deposition to the Danish waters appeared during the summer in the algae growth season. For the northern parts of the Baltic the highest depositions were distributed over most of the year.
DRIFTS and Knudsen cell study of the heterogeneous reactivity of SO2 and NO2 on mineral dust
Authors: Ullerstam M. , Johnson M. S. , Vogt R. , Ljungström E. 
Published: April 2010

Abstract. The heterogeneous oxidation of SO2 by NO2 on mineral dust was studied using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and a Knudsen cell. This made it possible to characterise, kinetically, both the formation of sulfate and nitrate as surface products and the gas phase loss of the reactive species. The gas phase loss rate was determined to be first order in both SO2 and NO2. From the DRIFTS experiment the uptake coefficient, γ, for the formation of sulfate was determined to be of the order of 10−10 using the BET area as the reactive surface area. No significant formation of sulfate was seen in the absence of NO2. The Knudsen cell study gave uptake coefficients of the order of 10−6 and 10-7 for SO2 and NO2, respectively. There was no significant difference in uptake when SO2 or NO2 were introduced individually compared to experiments in which SO2 and NO2 were present at the same time.
Measurements of photo-oxidation products from the reaction of a series of alkyl-benzenes with hydroxyl radicals during EXACT using comprehensive gas chromatography
Authors: Hamilton J. F. , Lewis A. C. , Bloss C. , Wagner V. , Henderson A. P. , Golding B. T. , Wirtz K. , Martin-Reviejo M. , Pilling M. J. 
Published: April 2010

Abstract. Photo-oxidation products from the reaction of a series of alkyl-benzenes, (benzene, toluene, p-xylene and 1,3,5-trimethyl-benzene) with hydroxyl radicals in the presence of NOx have been investigated using comprehensive gas chromatography (GCXGC). A GCXGC system has been developed which utilises valve modulation and independent separations as a function of both volatility and polarity. A number of carbonyl-type compounds were identified during a series of reactions carried out at the European Photoreactor (EUPHORE), a large volume outdoor reaction chamber in Valencia, Spain. Two litre chamber air samples were cryo-focused, with a sampling frequency of 30 min, allowing the evolution of species to be followed over oxidation periods of 3–6 h. To facilitate product identification, several carbonyl compounds, which were possible products of the photo-oxidation, were synthesised and used as reference standards. For toluene reactions, observed oxygenated intermediates found included the co-eluting pair a-angelicalactone/4-oxo-2-pentenal, maleic anhydride, citraconic anhydride, benzaldehyde and p-methyl benzoquinone. In the p-xylene experiment, the products identified were E/Z-hex-3-en-2,5-dione and citraconic anhydride. For 1,3,5-TMB reactions, the products identified were 3,5-dimethylbenzaldehyde, 3,5-dimethyl-3H-furan-2-one and 3-methyl-5-methylene-5H-furan-2-one. Preliminary quantification was carried out on identified compounds using liquid standards. Comparison of FTIR and GCXGC for the measurement of the parent aromatics generally showed good agreement.
Implementing growth and sedimentation of NAT particles in a global Eulerian model
Authors: van den Broek M. M. P. , Williams J. E. , Bregman A. 
Published: April 2010

Abstract. Here we present a concise and efficient algorithm to mimic the growth and sedimentation of Nitric Acid Trihydate (NAT) particles in the polar vortex in a state-of-the-art 3D chemistry transport model. The particle growth and sedimentation are calculated using the microphysical formulation of Carslaw et al. (2002). Once formed, NAT particles are transported in the model as tracers in the form of size-segregated quantities. Two different approaches were adopted for this purpose: one assuming a fixed particle number density ("FixedDens") and the other assuming a discrete set of particle diameter values ("FixedRad"). Simulations were performed for three separate 10-day periods during the 1999–2000 Arctic winter and compared to the results of an existing Lagrangian model study, which uses similar microphysics in a computationally more expensive method for the simulation of NAT particle growth. The resulting maximum particle sizes for both our approaches compare favourably at 96 hPa with those obtained from this previous model study, and also in-situ observations related to the size of large NAT particles. Comparisons were made with a standard equilibrium approach and the differences in the redistribution of HNO3 were found to be substantial. For both approaches the performance of the algorithm is rather insensitive to both the number of size bins and the shape of the size distribution. However, the percentage of HNO3 sequestered into NAT is critically dependent on the total number density of particles prescribed for each size bin.
Technical Note: A diagnostic for ozone contributions of various NOx emissions in multi-decadal chemistry-climate model simulations
Authors: Grewe V. 
Published: April 2010

Abstract. Nitrogen oxide (NOx=NO+NO2) emissions from various sources contribute to the ozone budget. The identification of these contributions is important, e.g. for the assessment of emissions from traffic. The non-linear character of ozone chemistry complicates the online diagnosis during multi-decadal chemistry-climate simulations. A methodology is suggested, which is efficient enough to be incorporated in multi-decadal simulations. Eight types of NOx emissions are included in the model. For each a NOy (=all N components, except N2 and N2O) tracer and an ozone tracer is included in the model, which experience the same emissions and loss processes like the online chemistry fields. To calculate the ozone changes caused by an individual NOx emission, the assumption is made that the NOx contributions from various sources are identical to the NOy contributions. To evaluate this method each NOx emission has been increased by 5% and a detailed error analysis is given. In the regions of the main impact of individual sources the potential error of the calculated contribution is significantly smaller than the contribution. Moreover, the changes caused by an increase of the emissions of 5% were detected with a higher accuracy than the potential errror of the absolut contribution.
OH and HO2 chemistry in clean marine air during SOAPEX-2
Authors: Sommariva R. , Haggerstone A.-L. , Carpenter L. J. , Carslaw N. , Creasey D. J. , Heard D. E. , Lee J. D. , Lewis A. C. , Pilling M. J. , Zádor J. 
Published: April 2010

Abstract. Model-measurement comparisons of HOx in extremely clean air ([NO]<3 ppt) are reported. Measurements were made during the second Southern Ocean Photochemistry Experiment (SOAPEX-2), held in austral summer 1999 at the Cape Grim Baseline Air Pollution Station in north-western Tasmania, Australia. The free-radical chemistry was studied using a zero-dimensional box-model based upon the Master Chemical Mechanism (MCM). Two versions of the model were used, with different levels of chemical complexity, to explore the role of hydrocarbons upon free-radical budgets under very clean conditions. The "detailed" model was constrained to measurements of CO, CH4 and 15 NMHCs, while the "simple" model contained only the CO and CH4 oxidation mechanisms, together with inorganic chemistry. The OH and HO2 (HOx) concentrations predicted by the two models agreed to within 5–10%. The model results were compared with the HOx concentrations measured by the FAGE (Fluorescence Assay by Gas Expansion) technique during four days of clean Southern Ocean marine boundary layer (MBL) air. The models overestimated OH concentrations by about 10% on two days and about 20% on the other two days. HO2 concentrations were measured during two of these days and the models overestimated the measured concentrations by about 40%. Better agreement with measured HO2 was observed by using data from several MBL aerosol measurements to estimate the aerosol surface area and by increasing the HO2 uptake coefficient to unity. This reduced the modelled HO2 overestimate by ~40%, with little effect on OH, because of the poor HO2 to OH conversion at the low ambient NOx concentrations. Local sensitivity analysis and Morris One-At-A-Time analysis were performed on the "simple" model, and showed the importance of reliable measurements of j(O1D) and [HCHO] and of the kinetic parameters that determine the efficiency of O(1D) to OH and HCHO to HO2 conversion. A 2σ standard deviation of 30–40% for OH and 25–30% for HO2 was estimated for the model calculations using a Monte Carlo technique coupled with Latin Hypercube Sampling (LHS). A rate of production analysis, which demonstrates the relevance of HCHO as a radical source, coupled with the poor performance of the models with respect to the concentrations of formaldehyde and peroxides, suggest that there are significant uncertainties in the chemical mechanism.
Validation of SCIAMACHY AMC-DOAS water vapour columns
Authors: Noël S. , Buchwitz M. , Bovensmann H. , Burrows J. P. 
Published: April 2010

Abstract. A first validation of water vapour total column amounts derived from measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) in the visible spectral region has been performed. For this purpose, SCIAMACHY water vapour data have been determined for the year 2003 using an extended version of the Differential Optical Absorption Spectroscopy (DOAS) method, called Air Mass Corrected (AMC-DOAS). The SCIAMACHY results are compared with corresponding water vapour measurements by the Special Sensor Microwave Imager (SSM/I) and with model data from the European Centre for Medium-Range Weather Forecasts (ECMWF). In confirmation of previous results it could be shown that SCIAMACHY derived water vapour columns are typically slightly lower than both SSM/I and ECMWF data, especially over ocean areas. However, these deviations are much smaller than the observed scatter of the data which is caused by the different temporal and spatial sampling and resolution of the data sets. For example, the overall difference with ECMWF data is only −0.05 g/cm2 whereas the typical scatter is in the order of 0.5 g/cm2. Both values show almost no variation over the year. In addition, first monthly means of SCIAMACHY water vapour data have been computed. The quality of these monthly means is currently limited by the availability of calibrated SCIAMACHY spectra. Nevertheless, first comparisons with ECMWF data show that SCIAMACHY (and similar instruments) are able to provide a new independent global water vapour data set.