Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Minor atmospheric components.
Articles de revues sur le sujet « Minor atmospheric components »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleurs articles de revues pour votre recherche sur le sujet « Minor atmospheric components ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les articles de revues sur diverses disciplines et organisez correctement votre bibliographie.
1
Damiani, A., M. Storini, M. Laurenza et C. Rafanelli. « Solar particle effects on minor components of the Polar atmosphere ». Annales Geophysicae 26, no 2 (26 février 2008) : 361–70. http://dx.doi.org/10.5194/angeo-26-361-2008.
Texte intégralRésumé :
Abstract. Solar activity can influence the Earth's environment, and in particular the ozone layer, by direct modulation of the e.m. radiation or through variability of the incoming cosmic ray flux (solar and galactic particles). In particular, solar energetic particles (SEPs) provide additional external energy to the terrestrial environment; they are able to interact with the minor constituents of the atmospheric layer and produce ionizations, dissociations, dissociative ionizations and excitations. This paper highlights the SEP effects on the chemistry of the upper atmosphere by analysing some SEP events recorded during 2005 in the descending phase of the current solar cycle. It is shown that these events can lead to short- (hours) and medium- (days) term ozone variations through catalytic cycles (e.g. HOx and NOx increases). We focus attention on the relationship between ozone and OH data (retrieved from MLS EOS AURA) for four SEP events: 17 and 20 January, 15 May and 8 September. We confirm that SEP effects are different on the night and day hemispheres at high latitudes.
2
Larin, I. K., et M. L. Kuskov. « Daytime and nighttime lifetimes of minor atmospheric components in the troposphere ». Russian Journal of Physical Chemistry B 8, no 2 (mars 2014) : 254–60. http://dx.doi.org/10.1134/s199079311402016x.
Texte intégral
3
Anacleto, J. F., R. K. Boyd, S. Pleasance, M. A. Quilliam, J. B. Howard, A. L. Lafleur et Y. Makarovsky. « Analysis of minor constituents in fullerene soots by LC–MS using a heated pneumatic nebulizer interface with atmospheric pressure chemical ionization ». Canadian Journal of Chemistry 70, no 10 (1 octobre 1992) : 2558–68. http://dx.doi.org/10.1139/v92-325.
Texte intégralRésumé :
The minor constituents of toluene extracts of three fullerene-rich materials have been characterized by on-line LC–MS techniques, incorporating both positive and negative ion mass spectra obtained by atmospheric pressure chemical ionization. Two of the materials were soots, produced by resistive heating of graphite in an inert atmosphere, from different commercial suppliers. The third material was obtained as a condensate from a controlled laminar flame, and was shown previously (Anacleto etal:, Rapid Commun. Mass Spectrom. 6, 214 (1992)) to contain significant quantities of compounds that behaved under the present LC–MS conditions as isomers of the C60 and C70 fullerenes, and which reverted to the latter upon heating. This finding was confirmed here, and extended to the higher clusters C76, C84, C90, and C94. One of the graphite-derived soots contained monoxides of the carbon clusters as the principal minor components, while the other soot contained hydrogenated species including C60H2, C60H4, C70H2, and (C60•CH4). The flame-generated material contained all of these minor constituents, together with complexes of C60 with larger aliphatic molecules as well as large quantities of polycyclic aromatic hydrocarbons and related species. Photo-oxidation of a purified C60 preparation, from the graphitic soot containing mostly monoxide impurities, was shown to lead to increased levels of the mono-, di-, and tri-oxides of C60.
4
Perrino, Cinzia, Maria Catrambone et Silvia Canepari. « Chemical Composition of PM10 in 16 Urban, Industrial and Background Sites in Italy ». Atmosphere 11, no 5 (8 mai 2020) : 479. http://dx.doi.org/10.3390/atmos11050479.
Texte intégralRésumé :
Italy is characterized by a very variable configuration in terms of altitude, proximity to the sea, latitude and the presence of industrial plants. This paper summarizes the chemical characterization of PM10 obtained from 38 sampling campaigns carried out in 16 sites in Italy during the years 2008–2018. Chemical determinations include all macro-components (six macro-elements, eight ions, elemental carbon and organic carbon). The sum of the individual components agrees well with the PM10 mass. The chemical composition of the atmospheric aerosol clearly reflects the variety in the Italian territory and the pronounced seasonal variations in the meteoclimatic conditions that characterize the country. Macro-sources reconstruction allowed us to identify and evaluate the strength of the main PM10 sources in different areas. On 10 sampling sites, the soluble and insoluble fractions of 23 minor and trace elements were also determined. Principal Component Analysis was applied to these data to highlight the relationship between the elemental composition of PM10 and the characteristics of the sampling sites.
5
Sen Gupta, Alexander, et Matthew H. England. « Coupled Ocean–Atmosphere–Ice Response to Variations in the Southern Annular Mode ». Journal of Climate 19, no 18 (15 septembre 2006) : 4457–86. http://dx.doi.org/10.1175/jcli3843.1.
Texte intégralRésumé :
Abstract The coupled ocean–atmosphere–ice response to variations in the Southern Annular Mode (SAM) is examined in the National Center for Atmospheric Research (NCAR) Community Coupled Climate Model (version 2). The model shows considerable skill in capturing the predominantly zonally symmetric SAM while regional deviations between model and observation SAM winds go a long way in explaining the generally small differences between simulated and observed SAM responses in the ocean and sea ice systems. Vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice. Both meridional and zonal components of ocean circulation are modified through Ekman transport, which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation. A heat budget analysis demonstrates a conspiring of oceanic meridional heat advection, surface heat fluxes, and changes in mixed layer depth, which acts in phase to imprint a strong circumpolar SAM signature onto sea surface temperatures (SSTs), while other oceanic processes, including vertical advection, are shown to play only a minor role in contrast to previous suggestions. Lagged correlations show that although the SAM is mainly controlled by internal atmospheric mechanisms, the thermal inertia of the ocean reimprints the SAM signature back onto surface air temperatures (SATs) on time scales longer than the initial atmospheric signal. Sea ice variability is well explained by a combination of atmospheric and oceanic dynamic and thermodynamic forcing, and by an albedo feedback mechanism that allows ice extent anomalies to persist for many months. Nonzonally symmetric components of the SAM winds, particularly in the region surrounding the Antarctic Peninsula, have important effects for other climate variables.
6
Taketani, F., Y. Kanaya, P. Pochanart, Y. Liu, J. Li, K. Okuzawa, K. Kawamura, Z. Wang et H. Akimoto. « Measurement of overall uptake coefficients for HO<sub>2</sub> ; radicals by aerosol particles sampled from ambient air at Mts. Tai and Mang (China) ». Atmospheric Chemistry and Physics 12, no 24 (17 décembre 2012) : 11907–16. http://dx.doi.org/10.5194/acp-12-11907-2012.
Texte intégralRésumé :
Abstract. HO2 uptake coefficients for ambient aerosol particles, collected on quartz fiber filter using a high-volume air sampler in China, were measured using an aerosol flow tube coupled with a chemical conversion/laser-induced fluorescence technique at 760 Torr and 298 K, with a relative humidity of 75%. Aerosol particles were regenerated with an atomizer using the water extracts from the aerosol particles. Over 10 samples, the measured HO2 uptake coefficients for the aerosol particles at the Mt. Tai site were ranged from 0.13 to 0.34, while those at the Mt. Mang site were in the range of 0.09–0.40. These values are generally larger than those previously reported for single-component particles, suggesting that reactions with the minor components such as metal ions and organics in the particle could contribute to the HO2 uptake. A box model calculation suggested that the heterogeneous loss of HO2 by ambient particles could significantly affect atmospheric HOx concentrations and chemistry.
7
Docherty, K. S., A. C. Aiken, J. A. Huffman, I. M. Ulbrich, P. F. DeCarlo, D. Sueper, D. R. Worsnop et al. « The 2005 Study of Organic Aerosols at Riverside (SOAR-1) : instrumental intercomparisons and fine particle composition ». Atmospheric Chemistry and Physics 11, no 23 (12 décembre 2011) : 12387–420. http://dx.doi.org/10.5194/acp-11-12387-2011.
Texte intégralRésumé :
Abstract. Multiple state-of-the-art instruments sampled ambient aerosol in Riverside, California during the 2005 Study of Organic Aerosols at Riverside (SOAR) to investigate the chemical composition and potential sources of fine particles (PMf) in the inland region of Southern California. In this paper, we briefly summarize the spatial, meteorological and gas-phase conditions during SOAR-1 (15 July–15 August), provide detailed intercomparisons of high-resolution aerosol mass spectrometer (HR-AMS) measurements against complementary measurements, and report the average composition of PMf including the composition of the organic fraction measured by the HR-AMS. Daily meteorology and gas-phase species concentrations were highly consistent, displaying clear diurnal cycles and weekday/weekend contrast. HR-AMS measurements of non-refractory submicron (NR-PM1) mass are consistent and highly correlated with those from a filter dynamics measurement system tapered-element oscillating microbalance (TEOM), while the correlation between HR-AMS and heated TEOM measurements is lower due to loss of high volatility species including ammonium nitrate from the heated TEOM. Speciated HR-AMS measurements are also consistent with complementary measurements as well as with measurements from a collocated compact AMS while HR-AMS OC is similar to standard semi-continuous Sunset measurements within the combined uncertainties of both instruments. A correction intended to account for the loss of semi-volatile OC from the Sunset, however, yields measurements ~30% higher than either HR-AMS or standard Sunset measurements. On average, organic aerosol (OA) was the single largest component of PMf. OA composition was investigated using both elemental analysis and positive matrix factorization (PMF) of HR-AMS OA spectra. Oxygen is the main heteroatom during SOAR-1, with O/C exhibiting a diurnal minimum of 0.28 during the morning rush hour and maximum of 0.42 during the afternoon. O/C is broadly anti-correlated with H/C, while N/C and S/C (excluding organonitrate (ON) and organosulfate (OS) functionalities) are far lower than O/C at about 0.015 and ~0.001, respectively. When ON and OS estimates are included O/C, N/C, and S/C increase by factors of 1.21, 2, and 30, respectively, while H/C changes are insignificant. The increase in these ratios implies that ON accounts for ~1/2 of the organic nitrogen while OS dominate organic sulfur at this location. Accounting for the estimated ON and OS also improves the agreement between anions and cations measured by HR-AMS by ~8%, while amines have only a very small impact (1%) on this balance. Finally, a number of primary and secondary OA components were resolved by PMF. Among these a hydrocarbon-like OA and two minor, local OA components, one of which was associated with amines, were attributed to primary emissions and contributed a minor fraction (~20%) of OA mass. The remaining OA mass was attributed to a number of secondary oxidized OA (OOA) components including the previously-identified low-volatility and semi-volatile OOA components. In addition, we also report for the first time the presence of two additional OOA components.
8
Proutsos, Nikolaos D., Aristotle Liakatas, Stavros G. Alexandris, Ioannis X. Tsiros, Dimitris Tigkas et George Halivopoulos. « Atmospheric Factors Affecting Global Solar and Photosynthetically Active Radiation Relationship in a Mediterranean Forest Site ». Atmosphere 13, no 8 (31 juillet 2022) : 1207. http://dx.doi.org/10.3390/atmos13081207.
Texte intégralRésumé :
Light availability and its composition in components affecting plant growth as photosynthetically active radiation (PAR), are of critical importance in agricultural and environmental research. In this work, radiation data for the period 2009–2014 in a forest site in Greece were analyzed to identify the effect of meteorological variables on the formation of the photosynthetically active to global solar radiation ratio. The temporal changes of the ratio are also discussed. Results showed that the ratio values are higher in summer (0.462) and lower in autumn (0.432), resulting in an annual average of 0.446. In addition, for the investigated site, which was characterized by relatively high water content in the atmosphere, the atmospheric water content and clearness were found to be the most influential factors in the composition of the global solar radiation in the wavelengths of PAR. On the contrary, temperature and related meteorological attributes (including relative humidity, vapor pressure deficit and saturation vapor pressure) were found to have minor effect.
9
Zvyagintsev, A. M., G. Kakadzhanova et O. A. Tarasova. « Influence of air mass transport directions on the seasonal variations of concentrations of minor gas atmospheric components in Europe ». Russian Meteorology and Hydrology 35, no 7 (juillet 2010) : 441–48. http://dx.doi.org/10.3103/s1068373910070022.
Texte intégral
10
Heidari, Mohammad Reza, Zhaoyang Song, Enrico Degregori, Jörg Behrens et Hendryk Bockelmann. « Concurrent calculation of radiative transfer in the atmospheric simulation in ECHAM-6.3.05p2 ». Geoscientific Model Development 14, no 12 (6 décembre 2021) : 7439–57. http://dx.doi.org/10.5194/gmd-14-7439-2021.
Texte intégralRésumé :
Abstract. The scalability of the atmospheric model ECHAM6 at low resolution, as used in palaeoclimate simulations, suffers from the limited number of grid points. As a consequence, the potential of current high-performance computing architectures cannot be used at full scale for such experiments, particularly within the available domain decomposition approach. Radiation calculations are a relatively expensive part of the atmospheric simulations, taking up to approximately 50 % or more of the total runtime. This current level of cost is achieved by calculating the radiative transfer only once in every 2 h of simulation. In response, we propose extending the available concurrency within the model further by running the radiation component in parallel with other atmospheric processes to improve scalability and performance. This paper introduces the concurrent radiation scheme in ECHAM6 and presents a thorough analysis of its impact on the performance of the model. It also evaluates the scientific results from such simulations. Our experiments show that ECHAM6 can achieve a speedup of over 1.9× using the concurrent radiation scheme. By performing a suite of stand-alone atmospheric experiments, we evaluate the influence of the concurrent radiation scheme on the scientific results. The simulated mean climate and internal climate variability by the concurrent radiation generally agree well with the classical radiation scheme, with minor improvements in the mean atmospheric circulation in the Southern Hemisphere and the atmospheric teleconnection to the Southern Annular Mode. This empirical study serves as a successful example that can stimulate research on other concurrent components in atmospheric modelling whenever scalability becomes challenging.
11
Topping, D. O., M. H. Barley et G. McFiggans. « The sensitivity of Secondary Organic Aerosol component partitioning to the predictions of component properties – Part 2 : Determination of particle hygroscopicity and its dependence on "apparent" ; volatility ». Atmospheric Chemistry and Physics 11, no 15 (3 août 2011) : 7767–79. http://dx.doi.org/10.5194/acp-11-7767-2011.
Texte intégralRésumé :
Abstract. A large number of calculations of absorptive partitioning of organic compounds have been conducted, making use of several methods to estimate pure component vapour pressures and activity coefficients (p0 and γi). The sensitivities of the predicted particle properties (density, hygroscopicity, CCN activation potential) to the choice of p0 and γi models and to the number of components used to represent the organic mixture have been systematically compared. The variability in theoretical hygroscopic growth factor attributable to the choice of estimation technique increases with decreasing mixture complexity. Generally there is low sensitivity to the choice of vapour pressure predictive technique. The inclusion of non-ideality is responsible for a larger difference in predicted growth factor, though still relatively minor. Assuming instantaneous equilibration of all semi-volatile on drying the aerosol to 0 % RH massively increases the sensitivity. Without such re-equilibration, the calculated growth factors are comparable to the low hygroscopicity of organic material widely measured in the laboratory and atmosphere. Allowing re-equilibration on drying produces a calculated hygroscopicity greater than measured for ambient organic material, and frequently close to those of common inorganic salts. Such a result has substantial implications on aerosol behaviour in instruments designed to measure hygroscopicity and on the degree of equilibration of semi-volatile components in the ambient atmosphere. The impacts of this variability on behaviour of particles as cloud condensation nuclei, on predicted cloud droplet number and uncertainty in radiative forcing are explored. When it is assumed only water evaporates on drying, the sensitivity in radiative forcing, "ΔF" to choice of p0 and γi estimation technique is low when the particle organic volume fraction is less than 55 %. Sensitivities increase with decreasing component complexity. If all components re-equilibrate on drying, the sensitivity of ΔF increases substantially for organic volume fractions as low as between 16 and 22 % depending on the complexity of the organic composition and assumed aerosol size distribution. The current study ignores the impact of predicted changes in particle size which will increase uncertainty in droplet number and forcing.
12
Stell, Angharad C., Luke M. Western, Tomás Sherwen et Matthew Rigby. « Atmospheric-methane source and sink sensitivity analysis using Gaussian process emulation ». Atmospheric Chemistry and Physics 21, no 3 (9 février 2021) : 1717–36. http://dx.doi.org/10.5194/acp-21-1717-2021.
Texte intégralRésumé :
Abstract. We present a method to efficiently approximate the response of atmospheric-methane mole fraction and δ13C–CH4 to changes in uncertain emission and loss parameters in a three-dimensional global chemical transport model. Our approach, based on Gaussian process emulation, allows relationships between inputs and outputs in the model to be efficiently explored. The presented emulator successfully reproduces the chemical transport model output with a root-mean-square error of 1.0 ppb and 0.05 ‰ for hemispheric-methane mole fraction and δ13C–CH4, respectively, for 28 uncertain model inputs. The method is shown to outperform multiple linear regression because it captures non-linear relationships between inputs and outputs as well as the interaction between model input parameters. The emulator was used to determine how sensitive methane mole fraction and δ13C–CH4 are to the major source and sink components of the atmospheric budget given current estimates of their uncertainty. We find that our current knowledge of the methane budget, as inferred through hemispheric mole fraction observations, is limited primarily by uncertainty in the global mean hydroxyl radical concentration and freshwater emissions. Our work quantitatively determines the added value of measurements of δ13C–CH4, which are sensitive to some uncertain parameters to which mole fraction observations on their own are not. However, we demonstrate the critical importance of constraining isotopic initial conditions and isotopic source signatures, small uncertainties in which strongly influence long-term δ13C–CH4 trends because of the long timescales over which transient perturbations propagate through the atmosphere. Our results also demonstrate that the magnitude and trend of methane mole fraction and δ13C–CH4 can be strongly influenced by the combined uncertainty in more minor components of the atmospheric budget, which are often fixed and assumed to be well-known in inverse-modelling studies (e.g. emissions from termites, hydrates, and oceans). Overall, our work provides an overview of the sensitivity of atmospheric observations to budget uncertainties and outlines a method which could be employed to account for these uncertainties in future inverse-modelling systems.
13
Ebert, M., A. Worringen, N. Benker, S. Mertes, E. Weingartner et S. Weinbruch. « Chemical composition and mixing-state of ice residuals sampled within mixed phase clouds ». Atmospheric Chemistry and Physics 11, no 6 (25 mars 2011) : 2805–16. http://dx.doi.org/10.5194/acp-11-2805-2011.
Texte intégralRésumé :
Abstract. During an intensive campaign at the high alpine research station Jungfraujoch, Switzerland, in February/March 2006 ice particle residuals within mixed-phase clouds were sampled using the Ice-counterflow virtual impactor (Ice-CVI). Size, morphology, chemical composition, mineralogy and mixing state of the ice residual and the interstitial (i.e., non-activated) aerosol particles were analyzed by scanning and transmission electron microscopy. Ice nuclei (IN) were identified from the significant enrichment of particle groups in the ice residual (IR) samples relative to the interstitial aerosol. In terms of number lead-bearing particles are enriched by a factor of approximately 25, complex internal mixtures with silicates or metal oxides as major components by a factor of 11, and mixtures of secondary aerosol and carbonaceous material (C-O-S particles) by a factor of 2. Other particle groups (sulfates, sea salt, Ca-rich particles, external silicates) observed in the ice-residual samples cannot be assigned unambiguously as IN. Between 9 and 24% of all IR are Pb-bearing particles. Pb was found as major component in around 10% of these particles (PbO, PbCl2). In the other particles, Pb was found as some 100 nm sized agglomerates consisting of 3–8 nm sized primary particles (PbS, elemental Pb). C-O-S particles are present in the IR at an abundance of 17–27%. The soot component within these particles is strongly aged. Complex internal mixtures occur in the IR at an abundance of 9–15%. Most IN identified at the Jungfraujoch station are internal mixtures containing anthropogenic components (either as main or minor constituent), and it is concluded that admixture of the anthropogenic component is responsible for the increased IN efficiency within mixed phase clouds. The mixing state appears to be a key parameter for the ice nucleation behaviour that cannot be predicted from the sole knowledge of the main component of an individual particle.
14
Haertel, Beate, Susanne Straßenburg, Katrin Oehmigen, Kristian Wende, Thomas von Woedtke et Ulrike Lindequist. « Differential Influence of Components Resulting from Atmospheric-Pressure Plasma on Integrin Expression of Human HaCaT Keratinocytes ». BioMed Research International 2013 (2013) : 1–9. http://dx.doi.org/10.1155/2013/761451.
Texte intégralRésumé :
Adequate chronic wound healing is a major problem in medicine. A new solution might be non-thermal atmospheric-pressure plasma effectively inactivating microorganisms and influencing cells in wound healing. Plasma components as, for example, radicals can affect cells differently. HaCaT keratinocytes were treated with Dielectric Barrier Discharge plasma (DBD/air, DBD/argon), ozone or hydrogen peroxide to find the components responsible for changes in integrin expression, intracellular ROS formation or apoptosis induction. Dependent on plasma treatment time reduction of recovered cells was observed with no increase of apoptotic cells, but breakdown of mitochondrial membrane potential. DBD/air plasma increased integrins and intracellular ROS. DBD/argon caused minor changes. About 100 ppm ozone did not influence integrins. Hydrogen peroxide caused similar effects compared to DBD/air plasma. In conclusion, effects depended on working gas and exposure time to plasma. Short treatment cycles did neither change integrins nor induce apoptosis or ROS. Longer treatments changed integrins as important for influencing wound healing. Plasma effects on integrins are rather attributed to induction of other ROS than to generation of ozone. Changes of integrins by plasma may provide new solutions of improving wound healing, however, conditions are needed which allow initiating the relevant influence on integrins without being cytotoxic to cells.
15
Troin, Magali, Richard Arsenault, Jean-Luc Martel et François Brissette. « Uncertainty of Hydrological Model Components in Climate Change Studies over Two Nordic Quebec Catchments ». Journal of Hydrometeorology 19, no 1 (1 janvier 2018) : 27–46. http://dx.doi.org/10.1175/jhm-d-17-0002.1.
Texte intégralRésumé :
Abstract Projected climate change effects on hydrology are investigated for the 2041–60 horizon under the A2 emission scenarios using a multimodel approach over two snowmelt-dominated catchments in Canada. An ensemble of 105 members was obtained by combining seven snow models (SMs), five potential evapotranspiration (PET) methods, and three hydrological model (HM) structures. The study was performed using high-resolution simulations from the Canadian Regional Climate Model (CRCM–15 km) driven by two members of the third-generation Canadian Coupled Global Climate Model (CGCM3). This study aims to compare various combinations of SM–PET–HM in terms of their ability to simulate streamflows under the current climate and to evaluate how they affect the assessment of the climate change–induced hydrological impacts at the catchment scale. The variability of streamflow response caused by the use of different SMs (degree-day versus degree-day/energy balance), PET methods (temperature-based versus radiation-based methods), and HM structures is evaluated, as well as the uncertainty due to the natural climate variability (CRCM intermember variability). The hydroclimatic simulations cover 1961–90 in the present period and 2041–60 in the future period. The ensemble spread of the climate change signal on streamflow is large and varies with catchments. Using the variance decomposition on three hydrologic indicators, the HM structure was found to make the most substantial contribution to uncertainty, followed by the choice of the PET methods or natural climate variability, depending on the hydrologic indicator and the catchment. Snow models played a minor, almost negligible role in the assessment of the climate change impacts on streamflow for the study catchments.
16
Koucká Knížová, Petra, Kateřina Podolská, Kateřina Potužníková, Daniel Kouba, Zbyšek Mošna, Josef Boška et Michal Kozubek. « Evidence of vertical coupling : meteorological storm Fabienne on 23 September 2018 and its related effects observed up to the ionosphere ». Annales Geophysicae 38, no 1 (17 janvier 2020) : 73–93. http://dx.doi.org/10.5194/angeo-38-73-2020.
Texte intégralRésumé :
Abstract. A severe meteorological storm system on the frontal border of cyclone Fabienne passing above central Europe was observed on 23–24 September 2018. Large meteorological systems are considered to be important sources of the wave-like variability visible/detectable through the atmosphere and even up to ionospheric heights. Significant departures from regular courses of atmospheric and ionospheric parameters were detected in all analyzed datasets through atmospheric heights. Above Europe, stratospheric temperature and wind significantly changed in coincidence with fast frontal transition (100–110 km h−1). Zonal wind at 1 and 0.1 hPa changes from the usual westward before the storm to eastward after the storm. With this change are connected changes in temperature where at 1 hPa the analyzed area is colder and at 0.1 hPa warmer. Within ionospheric parameters, we have detected significant wave-like activity occurring shortly after the cold front crossed the observational point. During the storm event, both by Digisonde DPS-4D and continuous Doppler sounding equipment, we have observed strong horizontal plasma flow shears and time-limited increase plasma flow in both the northern and western components of ionospheric drift. The vertical component of plasma flow during the storm event is smaller with respect to the corresponding values on preceding days. The analyzed event of an exceptionally fast cold front of cyclone Fabienne fell into the recovery phase of a minor–moderate geomagnetic storm observed as a negative ionospheric storm at European mid-latitudes. Hence, ionospheric observations consist both of disturbances induced by moderate geomagnetic storms and effects originating in convective activity in the troposphere. Nevertheless, taking into account a significant change in the global circulation pattern in the stratosphere, we conclude that most of the observed wave-like oscillations in the ionosphere during the night of 23–24 September can be directly attributed to the propagation of atmospheric waves launched on the frontal border (cold front) of cyclone Fabienne. The frontal system acted as an effective source of atmospheric waves propagating upward up to the ionosphere.
17
Khatiwala, S., A. Schmittner et J. Muglia. « Air-sea disequilibrium enhances ocean carbon storage during glacial periods ». Science Advances 5, no 6 (juin 2019) : eaaw4981. http://dx.doi.org/10.1126/sciadv.aaw4981.
Texte intégralRésumé :
The prevailing hypothesis for lower atmospheric carbon dioxide (CO2) concentrations during glacial periods is an increased efficiency of the ocean’s biological pump. However, tests of this and other hypotheses have been hampered by the difficulty to accurately quantify ocean carbon components. Here, we use an observationally constrained earth system model to precisely quantify these components and the role that different processes play in simulated glacial-interglacial CO2 variations. We find that air-sea disequilibrium greatly amplifies the effects of cooler temperatures and iron fertilization on glacial ocean carbon storage even as the efficiency of the soft-tissue biological pump decreases. These two processes, which have previously been regarded as minor, explain most of our simulated glacial CO2 drawdown, while ocean circulation and sea ice extent, hitherto considered dominant, emerge as relatively small contributors.
18
Pérez-Peña, Maria Paula, Jenny A. Fisher, Dylan B. Millet, Hisashi Yashiro, Ray L. Langenfelds, Paul B. Krummel et Scott H. Kable. « Evaluating the contribution of the unexplored photochemistry of aldehydes on the tropospheric levels of molecular hydrogen (H2) ». Atmospheric Chemistry and Physics 22, no 18 (21 septembre 2022) : 12367–86. http://dx.doi.org/10.5194/acp-22-12367-2022.
Texte intégralRésumé :
Abstract. Molecular hydrogen, H2, is one of the most abundant trace gases in the atmosphere. The main known chemical source of H2 in the atmosphere is the photolysis of formaldehyde and glyoxal. Recent laboratory measurements and ground-state photochemistry calculations have shown other aldehydes photodissociate to yield H2 as well. This aldehyde photochemistry has not been previously accounted for in atmospheric H2 models. Here, we used two atmospheric models to test the implications of the previously unexplored aldehyde photochemistry on the H2 tropospheric budget. We used the AtChem box model implementing the nearly chemically explicit Master Chemical Mechanism at three sites selected to represent variable atmospheric environments: London, Cabo Verde and Borneo. We conducted five box model simulations per site using varying quantum yields for the photolysis of 16 aldehydes and compared the results against a baseline. The box model simulations showed that the photolysis of acetaldehyde, propanal, methylglyoxal, glycolaldehyde and methacrolein yields the highest chemical production of H2. We also used the GEOS-Chem 3-D atmospheric chemical transport model to test the impacts of the new photolytic H2 source on the global scale. A new H2 simulation capability was developed in GEOS-Chem and evaluated for 2015 and 2016. We then performed a sensitivity simulation in which the photolysis reactions of six aldehyde species were modified to include a 1 % yield of H2. We found an increase in the chemical production of H2 over tropical regions where high abundance of isoprene results in the secondary generation of methylglyoxal, glycolaldehyde and methacrolein, ultimately yielding H2. We calculated a final increase of 0.4 Tg yr−1 in the global chemical production budget, compared to a baseline production of ∼41 Tg yr−1. Ultimately, both models showed that H2 production from the newly discovered photolysis of aldehydes leads to only minor changes in the atmospheric mixing ratios of H2, at least for the aldehydes tested here when assuming a 1 % quantum yield across all wavelengths. Our results imply that the previously missing photochemical source is a less significant source of model uncertainty than other components of the H2 budget, including emissions and soil uptake.
19
Krikken, F., et W. Hazeleger. « Arctic Energy Budget in Relation to Sea Ice Variability on Monthly-to-Annual Time Scales ». Journal of Climate 28, no 16 (10 août 2015) : 6335–50. http://dx.doi.org/10.1175/jcli-d-15-0002.1.
Texte intégralRésumé :
Abstract The large decrease in Arctic sea ice in recent years has triggered a strong interest in Arctic sea ice predictions on seasonal-to-decadal time scales. Hence, it is important to understand physical processes that provide enhanced predictability beyond persistence of sea ice anomalies. This study analyzes the natural variability of Arctic sea ice from an energy budget perspective, using 15 climate models from phase 5 of CMIP (CMIP5), and compares these results to reanalysis data. The authors quantify the persistence of sea ice anomalies and the cross correlation with the surface and top-of-atmosphere energy budget components. The Arctic energy balance components primarily indicate the important role of the seasonal ice–albedo feedback, through which sea ice anomalies in the melt season reemerge in the growth season. This is a robust anomaly reemergence mechanism among all 15 climate models. The role of the ocean lies mainly in storing heat content anomalies in spring and releasing them in autumn. Ocean heat flux variations play only a minor role. Confirming a previous (observational) study, the authors demonstrate that there is no direct atmospheric response of clouds to spring sea ice anomalies, but a delayed response is evident in autumn. Hence, there is no cloud–ice feedback in late spring and summer, but there is a cloud–ice feedback in autumn, which strengthens the ice–albedo feedback. Anomalies in insolation are positively correlated with sea ice variability. This is primarily a result of reduced multiple reflection of insolation due to an albedo decrease. This effect counteracts the ice-albedo effect up to 50%. ERA-Interim and Ocean Reanalysis System 4 (ORAS4) confirm the main findings from the climate models.
20
Shcherbak, Valeriia, Liudmyla Ganushchak-Yefimenko, Olena Nifatova, Ján Kosiba, Tomáš Holota et Valentуna Yatsenko. « The Use of University Biosystem Environmental Protection Platform to Prevent a New Outbreak of the COVID-19 Pandemic ». Acta Technologica Agriculturae 25, no 1 (1 mars 2022) : 47–52. http://dx.doi.org/10.2478/ata-2022-0008.
Texte intégralRésumé :
Abstract The purpose of this study was to determine the possibility of practical use of the Hackathon Platform for ecological protection of the university biosystem to prevent a new outbreak of the COVID-19 pandemic. The COVID-19 pandemic significantly affects companies and population’s behaviour. The most significant change occurred in the attitude of companies to the environment from technical and technological points of view. To increase their production sustainability, these companies are looking at the possibilities of waste recovery through sustainable recycling, or recovery of waste as a source of secondary raw material. One of the simplest ways is to use agricultural waste for energy purposes, bringing bioenergy to the forefront as a new area of Industry 4.0. The ALARA model was used to assess the quality of six biosystem components (atmospheric air, water resources, soil layer, the level of land pollution with chemicals and littering by the unauthorized dumps; sufficient volume of green planting on the territory). This allowed the development of management decisions and environmental protection measures based on the system of calculated indicators of potential environmental damage for each of six biosystem components. The forecast of plan implementation: the quality of four from among six biosystem components (atmospheric air, water resources, soil layer, sufficient volume of green planting on the territory) will increase on average by 30–40%. A minor improvement in the quality of the other biosystem components (approx. by 10%) raises concerns about the high probability of a new outbreak of the COVID-19 pandemic.
21
Saathoff, H., S. Henin, K. Stelmaszczyk, M. Petrarca, R. Delagrange, Z. Hao, J. Lüder et al. « Laser filament-induced aerosol formation ». Atmospheric Chemistry and Physics Discussions 12, no 11 (20 novembre 2012) : 29851–85. http://dx.doi.org/10.5194/acpd-12-29851-2012.
Texte intégralRésumé :
Abstract. Using the aerosol and cloud simulation chamber AIDA we investigated the laser filament induced particle formation in ambient air, humid synthetic air, humid nitrogen, argon-oxygen mixture, and pure argon in order to simulate the particle formation under realistic atmospheric conditions as well as to investigate the influence of typical gas-phase atmospheric constituents on the particle formation. Terawatt laser plasma filaments generated new particles in the size range 3 to 130 nm with particle production rates ranging from 1 × 107 to 5 × 109 cm−3 plasma s−1. In all cases the particle formation rates increased exponentially with the water content of the gas mixture. Furthermore, the presence of a few ppb of trace gases like SO2 and α-pinene clearly enhanced the particle yield by number, the latter also by mass. Our findings suggest that new particle formation is efficiently supported by acids generated by the photo-ionization of both major and minor components of the air, including N2, NH3, SO2 and organics.
22
Legrand, Michel R., et Robert J. Delmas. « Soluble Impurities in Four Antarctic Ice Cores Over the Last 30 000 Years ». Annals of Glaciology 10 (1988) : 116–20. http://dx.doi.org/10.3189/s0260305500004274.
Texte intégralRésumé :
The chemical composition of soluble impurities along the Dome C ice core covering approximately the last 30 000 years is reported and interpreted in terms of atmospheric contributions. Terrestrial and sea-salt inputs are known to have been much higher during the Last Glacial Maximum (LGM) than during the Holocene period. For this reason, the gas-derived compounds (mainly H2SO4 and HNO3) which dominate the chemistry of present-day snow are minor components in LGM snow. The exact calculation of each of the various contributions has been made possible by the determination of all major ions (H+, Na+, K+, NH4+, Mg2+, Ca2+, NO3−, SO42− and Cl−) in the samples. Three additional deep ice cores from other Antarctic areas have also been analyzed, but in a less comprehensive manner than the Dome C core. The differences observed at the four study sites increase the general understanding of the past atmospheric chemistry of the Southern Hemisphere.
23
Legrand, Michel R., et Robert J. Delmas. « Soluble Impurities in Four Antarctic Ice Cores Over the Last 30 000 Years ». Annals of Glaciology 10 (1988) : 116–20. http://dx.doi.org/10.1017/s0260305500004274.
Texte intégralRésumé :
The chemical composition of soluble impurities along the Dome C ice core covering approximately the last 30 000 years is reported and interpreted in terms of atmospheric contributions. Terrestrial and sea-salt inputs are known to have been much higher during the Last Glacial Maximum (LGM) than during the Holocene period. For this reason, the gas-derived compounds (mainly H2SO4 and HNO3) which dominate the chemistry of present-day snow are minor components in LGM snow. The exact calculation of each of the various contributions has been made possible by the determination of all major ions (H+, Na+, K+, NH4 +, Mg2+, Ca2+, NO3 −, SO4 2− and Cl−) in the samples. Three additional deep ice cores from other Antarctic areas have also been analyzed, but in a less comprehensive manner than the Dome C core. The differences observed at the four study sites increase the general understanding of the past atmospheric chemistry of the Southern Hemisphere.
24
Saathoff, H., S. Henin, K. Stelmaszczyk, M. Petrarca, R. Delagrange, Z. Hao, J. Lüder et al. « Laser filament-induced aerosol formation ». Atmospheric Chemistry and Physics 13, no 9 (3 mai 2013) : 4593–604. http://dx.doi.org/10.5194/acp-13-4593-2013.
Texte intégralRésumé :
Abstract. Using the aerosol and cloud simulation chamber AIDA, we investigated the laser filament induced particle formation in ambient air, humid synthetic air, humid nitrogen, argon–oxygen mixture, and pure argon in order to simulate the particle formation under realistic atmospheric conditions as well as to investigate the influence of typical gas-phase atmospheric constituents on the particle formation. Terawatt laser plasma filaments generated new particles in the size range 3 to 130 nm with particle production rates ranging from 1 × 107 to 5 × 109 cm−3 plasma s−1 for the given experimental conditions. In all cases the particle formation rates increased exponentially with the water content of the gas mixture. Furthermore, the presence of a few ppb of trace gases like SO2 and α-pinene clearly enhanced the particle yield by number, the latter also by mass. Our findings suggest that new particle formation is efficiently supported by oxidized species like acids generated by the photoionization of both major and minor components of the air, including N2, NH3, SO2 and organics.
25
Golobokova, L. P., V. E. Pavlov, I. V. Khvostov et T. V. Khodjer. « Distribution of some ions and minor gaseous components by concentrations in the atmospheric surface layer of some regions in Eastern Siberia and the Far East ». Izvestiya, Atmospheric and Oceanic Physics 47, no 3 (juin 2011) : 329–35. http://dx.doi.org/10.1134/s0001433811030066.
Texte intégral
26
Capotondi, Antonietta, Prashant D. Sardeshmukh et Lucrezia Ricciardulli. « The Nature of the Stochastic Wind Forcing of ENSO ». Journal of Climate 31, no 19 (octobre 2018) : 8081–99. http://dx.doi.org/10.1175/jcli-d-17-0842.1.
Texte intégralRésumé :
El Niño–Southern Oscillation (ENSO) is commonly viewed as a low-frequency tropical mode of coupled atmosphere–ocean variability energized by stochastic wind forcing. Despite many studies, however, the nature of this broadband stochastic forcing and the relative roles of its high- and low-frequency components in ENSO development remain unclear. In one view, the high-frequency forcing associated with the subseasonal Madden–Julian oscillation (MJO) and westerly wind events (WWEs) excites oceanic Kelvin waves leading to ENSO. An alternative view emphasizes the role of the low-frequency stochastic wind components in directly forcing the low-frequency ENSO modes. These apparently distinct roles of the wind forcing are clarified here using a recently released high-resolution wind dataset for 1990–2015. A spectral analysis shows that although the high-frequency winds do excite high-frequency Kelvin waves, they are much weaker than their interannual counterparts and are a minor contributor to ENSO development. The analysis also suggests that WWEs should be viewed more as short-correlation events with a flat spectrum at low frequencies that can efficiently excite ENSO modes than as strictly high-frequency events that would be highly inefficient in this regard. Interestingly, the low-frequency power of the rapid wind forcing is found to be higher during El Niño than La Niña events, suggesting a role also for state-dependent (i.e., multiplicative) noise forcing in ENSO dynamics.
27
Witthuhn, Jonas, Hartwig Deneke, Andreas Macke et Germar Bernhard. « Algorithms and uncertainties for the determination of multispectral irradiance components and aerosol optical depth from a shipborne rotating shadowband radiometer ». Atmospheric Measurement Techniques 10, no 2 (3 mars 2017) : 709–30. http://dx.doi.org/10.5194/amt-10-709-2017.
Texte intégralRésumé :
Abstract. The 19-channel rotating shadowband radiometer GUVis-3511 built by Biospherical Instruments provides automated shipborne measurements of the direct, diffuse and global spectral irradiance components without a requirement for platform stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Ångström exponent and precipitable water, can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be about 4 % for most channels within a 95 % confidence interval for shipborne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sunphotometer at a land site and a manually operated Microtops II sunphotometer on a ship is presented. Measurements deviate by less than 3 and 4 % on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for shipborne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth can be retrieved with an uncertainty of 0.02 for all channels within a 95 % confidence interval. The different methods to account for Rayleigh scattering and gas absorption in our scheme and in the Aerosol Robotic Network processing for Cimel sunphotometers lead to minor deviations. Relying on the cross calibration of the 940 nm water vapor channel with the Cimel sunphotometer, the column amount of precipitable water can be estimated with an uncertainty of ±0.034 cm.
28
Ruff, Steve R., Philip R. Christensen, Joshua L. Bandfield, Victoria E. Hamilton, Hugh H. Kieffer, Richard V. Morris, Melissa D. Lane et Michael C. Malin. « Martian Surface Composition as Determined by the MGS Thermal Emission Spectrometer ». Highlights of Astronomy 12 (2002) : 636. http://dx.doi.org/10.1017/s1539299600014477.
Texte intégralRésumé :
AbstractThe surface composition of Mars has been investigated using the Thermal Emission Spectrometer (TES) instrument during the mapping phase of the Mars Global Surveyor mission. The TES has mapped ~85% of the Martian surface at a resolution of 3-9 km. Separation of the atmospheric dust, water-ice cloud, CO2, water vapor, and surface components has been accomplished using radiative transfer and deconvolution. Two distinct surface compositional units have been mapped; (1) a basalt with plagioclase feldspar, Ca-rich pyroxene, minor sheet silicates; and (2) a basaltic andesite with silica glass, plagioclase, and minor pyroxene. Three large-scale (100’s km) accumulations of hematite have been found in Sinus Meridiani, Aram Chaos and Ophir/Candor Chasms. These regions are interpreted to be formed by aqueous precipitation under either ambient or hydrothermal conditions. No surfaces with detectable abundances of carbonate have been found. The albedo of the surface has been mapped with an absolute accuracy of ~1-2% and significant changes in surface albedo have occurred from the orbital measurements obtained by the Viking IRTM instrument.
29
DAS, DK. « Chemistry of monsoon rains over Calcutta, West Bengal ». MAUSAM 39, no 1 (1 janvier 1988) : 75–82. http://dx.doi.org/10.54302/mausam.v39i1.3194.
Texte intégralRésumé :
During the monsoon of 1984 (June-September), in all 50 filtered (0.45 IJom) rainwater samples were collected from Calcutta (West Bengall) and the samples were analysed for major, minor and trace elements, The analytical data, so far obtained, reveals that different chemical components are depended on different meteorological factors. Bicarbonate is predominant anion whereas calcium is predominant caution. Nearby sea seems to have greater influence on overall chemistry of rainwater, Most of the ions originate from marine origin but non-marine activity also plays an important role towards rainwater chemistry. Trace elements concentrations ID the rainwater have also been reported during the period of study. Further, a rough estimation of input of inorganic constituents (presently SO" NO3 and Cl) from the atmospheric precipitation over the West Bengal has been calculated and reported in this paper.
30
Toom, Matthijs den, Henk A. Dijkstra, Andrea A. Cimatoribus et Sybren S. Drijfhout. « Effect of Atmospheric Feedbacks on the Stability of the Atlantic Meridional Overturning Circulation ». Journal of Climate 25, no 12 (15 juin 2012) : 4081–96. http://dx.doi.org/10.1175/jcli-d-11-00467.1.
Texte intégralRésumé :
Abstract The impact of atmospheric feedbacks on the multiple equilibria (ME) regime of the Atlantic meridional overturning circulation (MOC) is investigated using a fully implicit hybrid coupled model (HCM). The HCM consists of a global ocean model coupled to an empirical atmosphere model that is based on linear regressions of the heat, net evaporative, and momentum fluxes generated by a fully coupled climate model onto local as well as Northern Hemisphere averaged sea surface temperatures. Using numerical continuation techniques, bifurcation diagrams are constructed for the HCM with the strength of an anomalous freshwater flux as the bifurcation parameter, which allows for an efficient first-order estimation of the effect of interactive surface fluxes on the MOC stability. The different components of the atmospheric fluxes are first considered individually and then combined. Heat feedbacks act to destabilize the present-day state of the MOC and to stabilize the collapsed state, thus leaving the size of the ME regime almost unaffected. In contrast, interactive freshwater fluxes cause a destabilization of both the present-day and collapsed states of the MOC. Wind feedbacks are found to have a minor impact. The joint effect of the three interactive fluxes is to narrow the range of ME. The shift of the saddle-node bifurcation that terminates the present-day state of the ocean is further investigated by adjoint sensitivity analysis of the overturning rate to surface fluxes. It is found that heat feedbacks primarily affect the MOC stability when they change the heat fluxes over the North Atlantic subpolar gyre, whereas interactive freshwater fluxes have an effect everywhere in the Atlantic basin.
31
Calvo, Natalia, et Rolando R. Garcia. « Wave Forcing of the Tropical Upwelling in the Lower Stratosphere under Increasing Concentrations of Greenhouse Gases ». Journal of the Atmospheric Sciences 66, no 10 (1 octobre 2009) : 3184–96. http://dx.doi.org/10.1175/2009jas3085.1.
Texte intégralRésumé :
Abstract Two simulations from the Whole Atmosphere Community Climate Model, covering the periods 1950–2003 and 1980–2050, are used to investigate the nature of the waves that force the increase of the tropical upwelling in the lower stratosphere as the concentration of greenhouse gases increases. Decomposition of the wave field resolved by the model into stationary and transient wavenumber spectra allows attribution of trends in the Eliassen–Palm (EP) flux and its divergence to specific wave components. This analysis reveals that enhanced dissipation of stationary planetary waves is the main driver of trends in the tropical upwelling in the lower stratosphere. The contribution of transient waves is smaller and is responsible mainly for trends in wave forcing in the subtropics and middle latitudes, which, however, provide only minor contributions to the mean tropical upwelling. Examination of individual wave structures shows that the stationary waves are tropical Rossby waves trapped in the upper troposphere and lower stratosphere, whereas the transient components are synoptic waves present in the subtropics and middle latitudes. The authors also present evidence that trends in resolved wave forcing in the lower stratosphere are due to both changes in wave transmissivity and changes in wave excitation, with the first mechanism dominating the behavior of the simulation during the last half of the twentieth century, while the second is clearly more important in the simulation during the first half of the twenty-first century.
32
Stober, Gunter, Diego Janches, Vivien Matthias, Dave Fritts, John Marino, Tracy Moffat-Griffin, Kathrin Baumgarten et al. « Seasonal evolution of winds, atmospheric tides, and Reynolds stress components in the Southern Hemisphere mesosphere–lower thermosphere in 2019 ». Annales Geophysicae 39, no 1 (7 janvier 2021) : 1–29. http://dx.doi.org/10.5194/angeo-39-1-2021.
Texte intégralRésumé :
Abstract. In this study we explore the seasonal variability of the mean winds and diurnal and semidiurnal tidal amplitude and phases, as well as the Reynolds stress components during 2019, utilizing meteor radars at six Southern Hemisphere locations ranging from midlatitudes to polar latitudes. These include Tierra del Fuego, King Edward Point on South Georgia island, King Sejong Station, Rothera, Davis, and McMurdo stations. The year 2019 was exceptional in the Southern Hemisphere, due to the occurrence of a rare minor stratospheric warming in September. Our results show a substantial longitudinal and latitudinal seasonal variability of mean winds and tides, pointing towards a wobbling and asymmetric polar vortex. Furthermore, the derived momentum fluxes and wind variances, utilizing a recently developed algorithm, reveal a characteristic seasonal pattern at each location included in this study. The longitudinal and latitudinal variability of vertical flux of zonal and meridional momentum is discussed in the context of polar vortex asymmetry, spatial and temporal variability, and the longitude and latitude dependence of the vertical propagation conditions of gravity waves. The horizontal momentum fluxes exhibit a rather consistent seasonal structure between the stations, while the wind variances indicate a clear seasonal behavior and altitude dependence, showing the largest values at higher altitudes during the hemispheric winter and two variance minima during the equinoxes. Also the hemispheric summer mesopause and the zonal wind reversal can be identified in the wind variances.
33
Philip, S. Y., M. Collins, G. J. van Oldenborgh et B. J. J. M. van den Hurk. « The role of atmosphere and ocean physical processes in ENSO in a perturbed physics coupled climate model ». Ocean Science 6, no 2 (20 avril 2010) : 441–59. http://dx.doi.org/10.5194/os-6-441-2010.
Texte intégralRésumé :
Abstract. We examine the behaviour of the El Niño – Southern Oscillation (ENSO) in an ensemble of global climate model simulations with perturbations to parameters in the atmosphere and ocean components respectively. The influence of the uncertainty in these parametrisations on ENSO are investigated systematically. The ensemble exhibits a range of different ENSO behaviour in terms of the amplitude and spatial structure of the sea surface temperature (SST) variability. The nature of the individual feedbacks that operate within the ENSO system are diagnosed using an Intermediate Complexity Model (ICM), which has been used previously to examine the diverse ENSO behaviour of the CMIP3 multi-model ensemble. Unlike in that case, the ENSO in these perturbed physics experiments is not principally controlled by variations in the mean climate state. Rather the parameter perturbations influence the ENSO characteristics by modifying the coupling feedbacks within the cycle. The associated feedbacks that contribute most to the ensemble variations are the response of SST to local wind variability and damping, followed by the response of SST to thermocline anomalies and the response of the zonal wind stress to those SST anomalies. Atmospheric noise amplitudes and oceanic processes play a relatively minor role.
34
Philip, S. Y., M. Collins, G. J. van Oldenborgh et B. J. J. M. van den Hurk. « The role of atmosphere and ocean physical processes in ENSO ». Ocean Science Discussions 6, no 3 (9 septembre 2009) : 2037–83. http://dx.doi.org/10.5194/osd-6-2037-2009.
Texte intégralRésumé :
Abstract. We examine the behaviour of the El Niño – Southern Oscillation (ENSO) in an ensemble of global climate model simulations with perturbations to parameters in the atmosphere and ocean components respectively. The influence of the uncertainty in these parametrisations on ENSO are investigated systematically. The ensemble exhibits a range of different ENSO behaviour in terms of the amplitude and spatial structure of the SST variability. The nature of the individual feedbacks that operate within the ENSO system are diagnosed using an Intermediate Complexity Model (ICM), which has been used previously to examine the diverse ENSO behaviour of the CMIP3 multi-model ensemble. Unlike in that case, the ENSO in these perturbed physics experiments is not principally controlled by variations in the mean climate state. Rather the parameter perturbations influence the ENSO characteristics by modifying the coupling feedbacks within the cycle. The associated feedbacks that contribute most to the ensemble variations are the response of SST to local wind variability and damping, followed by the response of SST to thermocline anomalies and the response of the zonal wind stress to those SST anomalies. Atmospheric noise amplitudes and oceanic processes play a relatively minor role.
35
Li, W. J., et L. Y. Shao. « Observation of nitrate coatings on atmospheric mineral dust particles ». Atmospheric Chemistry and Physics Discussions 8, no 6 (14 novembre 2008) : 19249–72. http://dx.doi.org/10.5194/acpd-8-19249-2008.
Texte intégralRésumé :
Abstract. Nitrate compounds have recently received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of nitrate-coated mineral particles in an individual particle scale in field study. The sample collection was conducted during brown haze and dust episodes occurred between 24 May and 21 June 2007 in Beijing, northern China. The sizes, morphologies, and compositions of mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM). 92% of the internally mixed mineral particles analyzed are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K- and S-rich coatings. The major coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with less sulfates and chlorides. These nitrate coatings strongly relate with the presence of alkaline mineral components (e.g., calcite and dolomite) within individual mineral particles. Calcium sulfate particles with the diameter from 10 to 500 nm were also detected within Ca(NO3)2 and Mg(NO3)2 coatings. Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heterogeneous reactions with two or more acidic gases (e.g., SO2, NO2, HCl, and HNO3). Mineral particles that acquire hygroscopic coatings tend to be more spherical and larger. Such changes enhance their light scattering and CCN activity, both of which have cooling effects on the climate.
36
Pook, M. J., J. S. Risbey, P. C. McIntosh, C. C. Ummenhofer, A. G. Marshall et G. A. Meyers. « The Seasonal Cycle of Blocking and Associated Physical Mechanisms in the Australian Region and Relationship with Rainfall ». Monthly Weather Review 141, no 12 (25 novembre 2013) : 4534–53. http://dx.doi.org/10.1175/mwr-d-13-00040.1.
Texte intégralRésumé :
Abstract The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°–35°C) and Australia (about 8°–17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April–October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts.
37
Yang, Chunxue, Simona Masina, Alessio Bellucci et Andrea Storto. « The Rapid Warming of the North Atlantic Ocean in the Mid-1990s in an Eddy-Permitting Ocean Reanalysis (1982–2013) ». Journal of Climate 29, no 15 (11 juillet 2016) : 5417–30. http://dx.doi.org/10.1175/jcli-d-15-0438.1.
Texte intégralRésumé :
Abstract The rapid warming in the mid-1990s in the North Atlantic Ocean is investigated by means of an eddy-permitting ocean reanalysis. Both the mean state and variability, including the mid-1990s warming event, are well captured by the reanalysis. An ocean heat budget applied to the subpolar gyre (SPG) region (50°–66°N, 60°–10°W) shows that the 1995–99 rapid warming is primarily dictated by changes in the heat transport convergence term while the surface heat fluxes appear to play a minor role. The mean negative temperature increment suggests a warm bias in the model and data assimilation corrects the mean state of the model, but it is not crucial to reconstruct the time variability of the upper-ocean temperature. The decomposition of the heat transport across the southern edge of the SPG into time-mean and time-varying components shows that the SPG warming is mainly associated with both the anomalous advection of mean temperature and the mean advection of temperature anomalies across the 50°N zonal section. The relative contributions of the Atlantic meridional overturning circulation (AMOC) and gyre circulation to the heat transport are also analyzed. It is shown that both the overturning and gyre components are relevant to the mid-1990s warming. In particular, the fast adjustment of the barotropic circulation response to the NAO drives the anomalous transport of mean temperature at the subtropical/subpolar boundary, while the slowly evolving AMOC feeds the large-scale advection of thermal anomalies across 50°N. The persistently positive phase of the NAO during the years prior to the rapid warming likely favored the cross-gyre heat transfer and the following SPG warming.
38
Matta, E., M. C. Facchini, S. Decesari, M. Mircea, F. Cavalli, S. Fuzzi, J. P. Putaud et A. Dell’Acqua. « Mass closure on the chemical species in size-segregated atmospheric aerosol collected in an urban area of the Po Valley, Italy ». Atmospheric Chemistry and Physics 3, no 3 (5 juin 2003) : 623–37. http://dx.doi.org/10.5194/acp-3-623-2003.
Texte intégralRésumé :
Abstract. A complete size segregated chemical characterisation was carried out for aerosol samples collected in the urban area of Bologna over a period of one year, using five-stage low pressure Berner impactors. An original dual-substrate technique was adopted to obtain samples suitable for a complete chemical characterisation. Total mass, inorganic, and organic components were analysed as a function of size, and a detailed characterisation of the water soluble organic compounds was also performed by means of a previously developed methodology, based on HPLC separation of organic compounds according to their acid character and functional group analysis by Proton Nuclear Magnetic Resonance. Chemical mass closure of the collected samples was reached to within a few percent on average in the submicron aerosol range, while a higher unknown fraction in the coarse aerosol range was attributed to soil-derived species not analysed in this experiment. Comparison of the functional group analysis results with model results simulating water soluble organic compound production by gas-to-particle conversion of anthropogenic VOCs showed that this pathway provides a minor contribution to the organic composition of the aerosol samples in the urban area of Bologna.
39
Lopez-Hilfiker, F. D., C. Mohr, M. Ehn, F. Rubach, E. Kleist, J. Wildt, Th F. Mentel et al. « Phase partitioning and volatility of secondary organic aerosol components formed from α-pinene ozonolysis and OH oxidation : the importance of accretion products and other low volatility compounds ». Atmospheric Chemistry and Physics 15, no 14 (16 juillet 2015) : 7765–76. http://dx.doi.org/10.5194/acp-15-7765-2015.
Texte intégralRésumé :
Abstract. We measured a large suite of gas- and particle-phase multi-functional organic compounds with a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) developed at the University of Washington. The instrument was deployed on environmental simulation chambers to study monoterpene oxidation as a secondary organic aerosol (SOA) source. We focus here on results from experiments utilizing an ionization method most selective towards acids (acetate negative ion proton transfer), but our conclusions are based on more general physical and chemical properties of the SOA. Hundreds of compounds were observed in both gas and particle phases, the latter being detected by temperature-programmed thermal desorption of collected particles. Particulate organic compounds detected by the FIGAERO–HR-ToF-CIMS are highly correlated with, and explain at least 25–50 % of, the organic aerosol mass measured by an Aerodyne aerosol mass spectrometer (AMS). Reproducible multi-modal structures in the thermograms for individual compounds of a given elemental composition reveal a significant SOA mass contribution from high molecular weight organics and/or oligomers (i.e., multi-phase accretion reaction products). Approximately 50 % of the HR-ToF-CIMS particle-phase mass is associated with compounds having effective vapor pressures 4 or more orders of magnitude lower than commonly measured monoterpene oxidation products. The relative importance of these accretion-type and other extremely low volatility products appears to vary with photochemical conditions. We present a desorption-temperature-based framework for apportionment of thermogram signals into volatility bins. The volatility-based apportionment greatly improves agreement between measured and modeled gas-particle partitioning for select major and minor components of the SOA, consistent with thermal decomposition during desorption causing the conversion of lower volatility components into the detected higher volatility compounds.
40
Wilson, D. G. « The Supplementary-Fired Exhaust-Heated Cycle for Coal, Wood and Refuse-Derived Fuel ». Proceedings of the Institution of Mechanical Engineers, Part A : Journal of Power and Energy 207, no 3 (août 1993) : 203–8. http://dx.doi.org/10.1243/pime_proc_1993_207_034_02.
Texte intégralRésumé :
An analysis is presented of a system that would enable refuse-derived fuel (RDF) (produced from, principally, paper) or other biomass (for example wood chips) or coal to be burned cleanly in a highly efficient gas turbine system of a size that would match the needs of many communities (a solid waste flow of 1000–3000 tons per day). The system consists of a gas turbine engine with two principal and several minor additions. The principal additions are a combustor to burn the RDF at approximately atmospheric pressure in the hot turbine exhaust flow and a high-temperature heat exchanger to transfer heat from this stream to the compressed air leaving the compressor. A design-point thermal efficiency of 55–60 per cent and high off-design efficiencies are predicted for the most favourable configuration with components designed for the purpose. About half the heat input would come from the RDF and half from conventional gas turbine liquid or gas fuel. In this paper the possible alternative configurations of such a plant are discussed, the thermodynamic implications are reviewed and some typical component performance values are introduced so that the overall plant performance can be predicted.
41
Li, W. J., et L. Y. Shao. « Observation of nitrate coatings on atmospheric mineral dust particles ». Atmospheric Chemistry and Physics 9, no 6 (17 mars 2009) : 1863–71. http://dx.doi.org/10.5194/acp-9-1863-2009.
Texte intégralRésumé :
Abstract. Nitrate compounds have received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of ambient nitrate-coated mineral particles on an individual particle scale. In this study, sample collection was conducted during brown haze and dust episodes between 24 May and 21 June 2007 in Beijing, northern China. Sizes, morphologies, and compositions of 332 mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) microanalyses. Structures of some mineral particles were verified using selected-area electron diffraction (SAED). TEM observation indicates that approximately 90% of the collected mineral particles are covered by visible coatings in haze samples whereas only 5% are coated in the dust sample. 92% of the analyzed mineral particles are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K- and S-rich coatings. The majority of coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with small amounts of sulfates and chlorides. These nitrate coatings are strongly correlated with the presence of alkaline mineral components (e.g., calcite and dolomite). CaSO4 particles with diameters from 10 to 500 nm were also detected in the coatings including Ca(NO3)2 and Mg(NO3)2. Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heterogeneous reactions with two or more acidic gases (e.g., SO2, NO2, HCl, and HNO3). Mineral particles that acquire hygroscopic nitrate coatings tend to be more spherical and larger, enhancing their light scattering and CCN activity, both of which have cooling effects on the climate.
42
Marsh, R., A. Yool, R. J. Myerscough, N. R. Edwards et J. G. Shepherd. « Incorporation of the C-GOLDSTEIN efficient climate model into the GENIE framework : the "genie_eb_go_gs" ; configuration of GENIE ». Geoscientific Model Development Discussions 2, no 1 (9 janvier 2009) : 1–79. http://dx.doi.org/10.5194/gmdd-2-1-2009.
Texte intégralRésumé :
Abstract. A computationally efficient, intermediate complexity ocean-atmosphere-sea ice model (C-GOLDSTEIN) is incorporated into the Grid ENabled Integrated Earth system modeling (GENIE) framework. This involved decoupling of the three component modules that were re-coupled in a modular way, to allow replacement with alternatives and coupling of further components within the framework. The climate model described here (genie_eb_go_gs) is the most basic version of GENIE in which atmosphere, ocean and sea ice all play an active role. Compared to the original model, latitudinal grid resolution has also been generalized to allow a wider range of surface grids to be used and an altered convection scheme has been added. Some other minor modifications and corrections have been applied. For four default meshes, and using the same default parameters as far as possible, we present the results from spin-up experiments. Evaluation of equilibrium states in terms of composite model-observation errors is demonstrated, with caveats regarding the use of un-tuned key parameters. For each mesh, we also carry out four standard climate experiments, based on international protocols: (i) equilibrium climate response (sensitivity) to doubled atmospheric CO2 concentration; (ii) transient climate response to CO2 concentration, increasing at 1% per annum, until doubling; (iii) response of the Atlantic meridional overturning circulation to freshwater hosing over 100 years; and (iv) hysteresis of the overturning circulation under slowly-varied freshwater forcing. Climate sensitivity and transient climate response lie in the ranges 2.85–3.13°C and 1.67–1.97°C respectively. The Atlantic overturning collapses under 0.1 Sv hosing, and subsequently recovers, for one of the meshes. Hosing at 1.0 Sv, the overturning collapses, and remains collapsed, on all four meshes. The hysteresis experiments reveal a wide range in stability of the initial state, from strongly monostable to strongly bistable. The dependencies of experimental results on choice of mesh are thus highlighted and discussed.
43
O'Sullivan, D., B. J. Murray, T. L. Malkin, T. Whale, N. S. Umo, J. D. Atkinson, H. C. Price, K. J. Baustian, J. Browse et M. E. Webb. « Ice nucleation by soil dusts : relative importance of mineral dust and biogenic components ». Atmospheric Chemistry and Physics Discussions 13, no 8 (5 août 2013) : 20275–317. http://dx.doi.org/10.5194/acpd-13-20275-2013.
Texte intégralRésumé :
Abstract. Agricultural dust emissions have been estimated to contribute around 20% to the global dust burden. In contrast to dusts from arid source regions, the ice-nucleating abilities of which have been relatively well studied, soil dusts from fertile sources often contain a substantial fraction of organic matter. Using an experimental methodology which is sensitive to a wide range of ice nucleation efficiencies, we have characterised the immersion mode ice-nucleating activities of dusts extracted from fertile soils collected at four locations around England. By controlling droplet sizes, which ranged in volume from 10−12 to 10−6 L, we have been able to determine the ice nucleation behaviour of soil dust particles at temperatures ranging from 267 K (−6 °C) down to the homogeneous limit of freezing at about 237 K (−36 °C). At temperatures above 258 K (−15 °C) we find that the ice-nucleating activity of soil dusts is diminished by heat treatment or digestion with hydrogen peroxide, suggesting that the ice nuclei stem from biogenic components in the soil. However, below 258 K, we find that the ice active site densities tend towards those expected from the mineral components in the soils, suggesting that the inorganic fraction of soil dusts, in particular the K-feldspar fraction, becomes increasingly important in the initiation of the ice phase at lower temperatures. We conclude that although only a relatively minor contributor to the global atmospheric dust burden, the enhanced IN activities of dusts generated from agricultural activities may play an important role in cloud glaciation, particularly at temperatures above 258 K.
44
Chen, Shengqian, Andrew J. Majda et Samuel N. Stechmann. « Tropical–Extratropical Interactions with the MJO Skeleton and Climatological Mean Flow ». Journal of the Atmospheric Sciences 73, no 10 (28 septembre 2016) : 4101–16. http://dx.doi.org/10.1175/jas-d-16-0041.1.
Texte intégralRésumé :
Abstract Simplified asymptotic models are developed to investigate tropical–extratropical interactions. Two kinds of interactions are illustrated in the model: (i) MJO initiation through extraction of energy from barotropic Rossby waves and (ii) MJO termination via energy transfer to extratropical Rossby waves. A new feature, in comparison to previous simplified models, is that here these waves interact directly in the presence of a climatological mean flow given by the Walker circulation. The simplified models are systems of ordinary differential equations (ODEs) for the amplitudes of barotropic Rossby waves and the MJO, and they are systematically derived from the MJO skeleton model by using multiscale asymptotics. The simplified ODEs allow for rapid investigation of a wide range of model parameters, such as initial conditions and wind shear. Zonally uniform wind shear is shown to have only a minor effect on these interactions here, in contrast to the important role of the zonally varying wind shear associated with the Walker circulation. The models illustrate some realistic features of tropical–extratropical interactions on intraseasonal to seasonal time scales. A key aspect of the models here is that the water vapor and convective activities are interactive components of the model, rather than specified external heating sources.
45
Papadopoulos, Vassilis P., Simon A. Josey, Aristides Bartzokas, Samuel Somot, Simon Ruiz et Paraskevi Drakopoulou. « Large-Scale Atmospheric Circulation Favoring Deep- and Intermediate-Water Formation in the Mediterranean Sea ». Journal of Climate 25, no 18 (23 mars 2012) : 6079–91. http://dx.doi.org/10.1175/jcli-d-11-00657.1.
Texte intégralRésumé :
Abstract Atmospheric circulation patterns that are conducive to extreme ocean heat loss are investigated at four sites of special interest in the Mediterranean Sea. The Gulf of Lions, the South Adriatic Sea, the Cretan Sea, and the Levantine Sea are areas where anomalously high winter heat loss may lead to deep- or intermediate-water formation. At each of the above sites, the atmospheric circulation during such events is derived by averaging the sea level pressure (SLP) fields during the lower decile of the wintertime series of the net heat exchange. A relatively simple SLP pattern dominated by an anticyclone over northwestern Europe with a weaker cyclone to the southeast is found to be associated with strong heat loss in the selected sites with minor variations in pattern structure depending on the site. The SLP composite pattern reflects the combined effect of different atmospheric modes of variability and the authors consider the impacts on heat loss of a number of these modes (North Atlantic Oscillation, east Atlantic pattern, east Atlantic–west Russia pattern, and Scandinavian pattern), together with the North Sea–Caspian pattern and the Mediterranean index. The extremes in heat loss are strongly connected with the intensity and the positions of the poles of these patterns that modulate, through the necessary SLP gradient and associated northerlies, the transfer of cold and dry air over the areas of dense-water formation. Analysis of air–sea temperature difference, specific humidity, and evaporation anomalies indicates that the extremes of the net heat fluxes are primarily due to the latent and sensible heat flux components.
46
Matta, E., M. C. Facchini, S. Decesari, M. Mircea, F. Cavalli, S. Fuzzi, J. P. Putaud et A. Dell’Acqua. « Chemical mass balance of size-segregated atmospheric aerosol in an urban area of the Po Valley, Italy ». Atmospheric Chemistry and Physics Discussions 2, no 6 (20 novembre 2002) : 2167–208. http://dx.doi.org/10.5194/acpd-2-2167-2002.
Texte intégralRésumé :
Abstract. A complete size segregated chemical characterisation was carried out for aerosol samples collected in the urban area of Bologna over a period of one year, using five-stage low pressure Berner impactors. An original dual-substrate technique was adopted to obtain samples suitable for a complete chemical characterisation. Total mass, inorganic, and organic components were analysed as a function of size, and a detailed characterisation of the water soluble organic compounds was also performed by means of a previously developed methodology, based on HPLC separation of organic compounds according to their acid character and functional group analysis by Proton Nuclear Magnetic Resonance. Chemical mass closure of the collected samples was reached to within a few percent on average in the submicron aerosol range, while a higher unknown fraction in the coarse aerosol range was attributed to soil-derived species not analysed in this experiment. Comparison of the functional group analysis results with model results simulating water soluble organic compound production by gas-to-particle conversion of anthropogenic VOCs showed that this pathway provides a minor contribution to the organic composition of the aerosol samples in the urban area of Bologna.
47
Fröhlich, R., V. Crenn, A. Setyan, C. A. Belis, F. Canonaco, O. Favez, V. Riffault et al. « ACTRIS ACSM intercomparison – Part 2 : Intercomparison of ME-2 organic source apportionment results from 15 individual, co-located aerosol mass spectrometers ». Atmospheric Measurement Techniques 8, no 6 (24 juin 2015) : 2555–76. http://dx.doi.org/10.5194/amt-8-2555-2015.
Texte intégralRésumé :
Abstract. Chemically resolved atmospheric aerosol data sets from the largest intercomparison of the Aerodyne aerosol chemical speciation monitors (ACSMs) performed to date were collected at the French atmospheric supersite SIRTA. In total 13 quadrupole ACSMs (Q-ACSM) from the European ACTRIS ACSM network, one time-of-flight ACSM (ToF-ACSM), and one high-resolution ToF aerosol mass spectrometer (AMS) were operated in parallel for about 3 weeks in November and December~2013. Part 1 of this study reports on the accuracy and precision of the instruments for all the measured species. In this work we report on the intercomparison of organic components and the results from factor analysis source apportionment by positive matrix factorisation (PMF) utilising the multilinear engine 2 (ME-2). Except for the organic contribution of mass-to-charge ratio m/z 44 to the total organics (f44), which varied by factors between 0.6 and 1.3 compared to the mean, the peaks in the organic mass spectra were similar among instruments. The m/z 44 differences in the spectra resulted in a variable f44 in the source profiles extracted by ME-2, but had only a minor influence on the extracted mass contributions of the sources. The presented source apportionment yielded four factors for all 15 instruments: hydrocarbon-like organic aerosol (HOA), cooking-related organic aerosol (COA), biomass burning-related organic aerosol (BBOA) and secondary oxygenated organic aerosol (OOA). ME-2 boundary conditions (profile constraints) were optimised individually by means of correlation to external data in order to achieve equivalent / comparable solutions for all ACSM instruments and the results are discussed together with the investigation of the influence of alternative anchors (reference profiles). A comparison of the ME-2 source apportionment output of all 15 instruments resulted in relative standard deviations (SD) from the mean between 13.7 and 22.7 % of the source's average mass contribution depending on the factors (HOA: 14.3 ± 2.2 %, COA: 15.0 ± 3.4 %, OOA: 41.5 ± 5.7 %, BBOA: 29.3 ± 5.0 %). Factors which tend to be subject to minor factor mixing (in this case COA) have higher relative uncertainties than factors which are recognised more readily like the OOA. Averaged over all factors and instruments the relative first SD from the mean of a source extracted with ME-2 was 17.2 %.
48
Fröhlich, R., V. Crenn, A. Setyan, C. A. Belis, F. Canonaco, O. Favez, V. Riffault et al. « ACTRIS ACSM intercomparison – Part 2 : Intercomparison of ME-2 organic source apportionment results from 15 individual, co-located aerosol mass spectrometers ». Atmospheric Measurement Techniques Discussions 8, no 2 (4 février 2015) : 1559–613. http://dx.doi.org/10.5194/amtd-8-1559-2015.
Texte intégralRésumé :
Abstract. Chemically resolved atmospheric aerosol data sets from the largest intercomparison of the Aerodyne aerosol chemical speciation monitors (ACSM) performed to date were collected at the French atmospheric supersite SIRTA. In total 13 quadrupole ACSMs (Q-ACSM) from the European ACTRIS ACSM network, one time-of-flight ACSM (ToF-ACSM), and one high-resolution ToF aerosol mass spectrometer (AMS) were operated in parallel for about three weeks in November and December 2013. Part 1 of this study reports on the accuracy and precision of the instruments for all the measured species. In this work we report on the intercomparison of organic components and the results from factor analysis source apportionment by positive matrix factorisation (PMF) utilising the multilinear engine 2 (ME-2). Except for the organic contribution of m/z 44 to the total organics (f44), which varied by factors between 0.6 and 1.3 compared to the mean, the peaks in the organic mass spectra were similar among instruments. The m/z 44 differences in the spectra resulted in a variable f44 in the source profiles extracted by ME-2, but had only a minor influence on the extracted mass contributions of the sources. The presented source apportionment yielded four factors for all 15 instruments: hydrocarbon-like organic aerosol (HOA), cooking-related organic aerosol (COA), biomass burning-related organic aerosol (BBOA) and secondary oxygenated organic aerosol (OOA). Individual application and optimisation of the ME-2 boundary conditions (profile constraints) are discussed together with the investigation of the influence of alternative anchors (reference profiles). A comparison of the ME-2 source apportionment output of all 15 instruments resulted in relative SD from the mean between 13.7 and 22.7% of the source's average mass contribution depending on the factors (HOA: 14.3 ± 2.2%, COA: 15.0 ± 3.4%, OOA: 41.5 ± 5.7%, BBOA: 29.3 ± 5.0%). Factors which tend to be subject to minor factor mixing (in this case COA) have higher relative uncertainties than factors which are recognised more readily like the OOA. Averaged over all factors and instruments the relative first SD from the mean of a source extracted with ME-2 was 17.2%.
49
Michailoudi, Georgia, Jack J. Lin, Hayato Yuzawa, Masanari Nagasaka, Marko Huttula, Nobuhiro Kosugi, Theo Kurtén, Minna Patanen et Nønne L. Prisle. « Aqueous-phase behavior of glyoxal and methylglyoxal observed with carbon and oxygen K-edge X-ray absorption spectroscopy ». Atmospheric Chemistry and Physics 21, no 4 (25 février 2021) : 2881–94. http://dx.doi.org/10.5194/acp-21-2881-2021.
Texte intégralRésumé :
Abstract. Glyoxal (CHOCHO) and methylglyoxal (CH3C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by the addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na2SO4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, supported by quantum chemical calculations we identified not only C–H, C=O and C–OH bonds, but also fingerprints of C–OH(CH2) and C=C bonds. The relatively low intensity of C=O transitions implies that the monohydrated form of methylglyoxal is not favored in the solutions. Instead, the spectral intensity is stronger in regions where products of aldol condensation and enol tautomers of the monohydrates contribute. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that XAS in the near-edge region is not very sensitive to these intermolecular organic–inorganic interactions at the studied concentrations. The identified structures of glyoxal and methylglyoxal in an aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution to secondary organic aerosol formation.
50
Kim, Sungwoo, Brian M. Lerner, Donna T. Sueper et Gabriel Isaacman-VanWertz. « Comprehensive detection of analytes in large chromatographic datasets by coupling factor analysis with a decision tree ». Atmospheric Measurement Techniques 15, no 17 (5 septembre 2022) : 5061–75. http://dx.doi.org/10.5194/amt-15-5061-2022.
Texte intégralRésumé :
Abstract. Environmental samples typically contain hundreds or thousands of unique organic compounds, and even minor components may provide valuable insight into their sources and transformations. To understand atmospheric processes, individual components are frequently identified and quantified using gas chromatography–mass spectrometry. However, due to the complexity and frequently variable nature of such data, data reduction is a significant bottleneck in analysis. Consequently, only a subset of known analytes is often reported for a dataset, and large amounts of potentially useful data are discarded. We present an automated approach of cataloging and potentially identifying all analytes in a large chromatographic dataset and demonstrate the utility of our approach in an analysis of ambient aerosols. We use a coupled factor analysis–decision tree approach to deconvolute peaks and comprehensively catalog nearly all analytes in a dataset. Positive matrix factorization (PMF) of small subsections of multiple chromatograms is applied to extract factors that represent chromatographic profiles and mass spectra of potential analytes, in which peaks are detected. A decision tree based on peak parameters (e.g., location, width, and height), relative ratios of those parameters, peak shape, noise, retention time, and mass spectrum is applied to discard erroneous peaks and combine peaks determined to represent the same analyte. With our approach, all analytes within the small section of the chromatogram are cataloged, and the process is repeated for overlapping sections across the chromatogram, generating a complete list of the retention times and estimated mass spectra of all peaks in a dataset. We validate this approach using samples of known compounds and demonstrate the separation of poorly resolved peaks with similar mass spectra and the resolution of peaks that appear in only a fraction of chromatograms. As a case study, this method is applied to a complex real-world dataset of the composition of atmospheric particles, in which more than 1100 unique chromatographic peaks are resolved, and the corresponding peak information along with mass spectra are cataloged.