Articoli di riviste: "Chemical tracers"

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Cao, Viet, Mario Schaffer, Reza Taherdangkoo e Tobias Licha. "Solute Reactive Tracers for Hydrogeological Applications: A Short Review and Future Prospects". Water 12, n. 3 (28 febbraio 2020): 653. http://dx.doi.org/10.3390/w12030653.

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Tracer testing is a mature technology used for characterizing aquatic flow systems. To gain more insights from tracer tests a combination of conservative (non-reactive) tracers together with at least one reactive tracer is commonly applied. The reactive tracers can provide unique information about physical, chemical, and/or biological properties of aquatic systems. Although, previous review papers provide a wide coverage on conservative tracer compounds there is no systematic review on reactive tracers yet, despite their extensive development during the past decades. This review paper summarizes the recent development in compounds and compound classes that are exploitable and/or have been used as reactive tracers, including their systematization based on the underlying process types to be investigated. Reactive tracers can generally be categorized into three groups: (1) partitioning tracers, (2) kinetic tracers, and (3) reactive tracers for partitioning. The work also highlights the potential for future research directions. The recent advances from the development of new tailor-made tracers might overcome existing limitations.

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Braconnier, Benjamin, Christophe Preux, Frédéric Douarche e Bernard Bourbiaux. "MUSCL scheme for Single Well Chemical Tracer Test simulation, design and interpretation". Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 74 (2019): 10. http://dx.doi.org/10.2516/ogst/2018090.

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Our paper presents an improved numerical scheme to simulate Single Well Chemical Tracer Test (SWCTT) method. SWCTT is mainly applied to determine the residual oil saturation of reservoirs. It consists in injecting an aqueous slug of a primary tracer into the reservoir formation and displacing it at a certain distance from the well. This tracer is partly miscible with oil on the one hand, and generates in situ a secondary tracer on the other hand. As a consequence, a shift is observed between the primary and the secondary tracers arrival times when production is resumed. This time shift is used to evaluate the residual oil saturation. In our paper, we propose a numerical scheme based on a fractional time stepping technique to decouple the resolution of the phases mass conservation equations and the chemical tracers mole conservation equations. For the phases resolution, we use an implicit scheme to ensure stability and robustness. For the chemical tracers, we propose an explicit second-order scheme in time and in space via MUSCL technique to improve the tracers time-shift calculation. The proposed numerical method is implemented on a realistic simulation model consisting of a vertical well crossing a reservoir consisting of a stack of homogeneous layers. By reducing the numerical dispersion, the proposed scheme improves the accuracy of predicted concentration profiles, without significantly increasing the computation time. Finally, the advantages of using a second-order scheme for residual oil saturation assessment are discussed on the basis of a radial 1D mesh convergence study.

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Jöckel, P., A. Kerkweg, J. Buchholz, H. Tost, R. Sander e A. Pozzer. "Technical Note: Coupling of chemical processes with the Modular Earth Submodel System (MESSy) submodel TRACER". Atmospheric Chemistry and Physics Discussions 7, n. 6 (23 novembre 2007): 17069–97. http://dx.doi.org/10.5194/acpd-7-17069-2007.

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Abstract. The implementation of processes related to chemistry into Earth System Models and their coupling within such systems requires the consistent description of the chemical species involved. We provide a tool (written in Fortran95) to structure and manage information about constituents, herein after referred to as tracers, namely the Modular Earth Submodel System (MESSy) generic (i.e., infrastructure) submodel TRACER. With TRACER it is possible to define a multitude of tracer sets, depending on the spatio-temporal representation (i.e., the grid structure) of the model. The required information about a specific chemical species is split into the static meta-information about the characteristics of the species, and its (generally in time and space variable) abundance in the corresponding representation. TRACER moreover includes two submodels. One is TRACER_FAMILY, an implementation of the tracer family concept. It distinguishes between two types: type-1 families are usually applied to handle strongly related tracers (e.g., fast equilibrating species) for a specific process (e.g., advection). In contrast to this, type-2 families are applied for tagging techniques, in which specific species are artificially decomposed and associated with additional information, in order to conserve the linear relationship between the family and its members. The second submodel is TRACER_PDEF, which corrects and budgets numerical negative overshoots that arise in many process implementations due to the numerical limitations (limited precision, rounding errors). The submodel therefore guarantees the positive definiteness of the tracers and stabilises the integration scheme. As a by-product, it further provides a global tracer mass diagnostic. Last but not least, we present the submodel PTRAC for the definition of prognostic tracers via a Fortran95 namelist. TRACER with its submodels and PTRAC can readily be applied to a variety of models without further requirements. The code and a documentation is included in the electronic supplement.

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Jöckel, P., A. Kerkweg, J. Buchholz-Dietsch, H. Tost, R. Sander e A. Pozzer. "Technical Note: Coupling of chemical processes with the Modular Earth Submodel System (MESSy) submodel TRACER". Atmospheric Chemistry and Physics 8, n. 6 (19 marzo 2008): 1677–87. http://dx.doi.org/10.5194/acp-8-1677-2008.

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Abstract. The implementation of processes related to chemistry into Earth System Models and their coupling within such systems requires the consistent description of the chemical species involved. We provide a tool (written in Fortran95) to structure and manage information about constituents, hereinafter referred to as tracers, namely the Modular Earth Submodel System (MESSy) generic (i.e., infrastructure) submodel TRACER. With TRACER it is possible to define a multitude of tracer sets, depending on the spatio-temporal representation (i.e., the grid structure) of the model. The required information about a specific chemical species is split into the static meta-information about the characteristics of the species, and its (generally in time and space variable) abundance in the corresponding representation. TRACER moreover includes two submodels. One is TRACER_FAMILY, an implementation of the tracer family concept. It distinguishes between two types: type-1 families are usually applied to handle strongly related tracers (e.g., fast equilibrating species) for a specific process (e.g., advection). In contrast to this, type-2 families are applied for tagging techniques. Tagging means the artificial decomposition of one or more species into parts, which are additionally labelled (e.g., by the region of their primary emission) and then processed as the species itself. The type-2 family concept is designed to conserve the linear relationship between the family and its members. The second submodel is TRACER_PDEF, which corrects and budgets numerical negative overshoots that arise in many process implementations due to the numerical limitations (e.g., rounding errors). The submodel therefore guarantees the positive definiteness of the tracers and stabilises the integration scheme. As a by-product, it further provides a global tracer mass diagnostic. Last but not least, we present the submodel PTRAC, which allows the definition of tracers via a Fortran95 namelist, as a complement to the standard tracer definition by application of the TRACER interface routines in the code. TRACER with its submodels and PTRAC can readily be applied to a variety of models without further requirements. The code and a documentation are included in the electronic supplement.

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Bayet, E., T. A. Davis, T. A. Bell e S. Viti. "Chemical tracers of high-metallicity environments". Monthly Notices of the Royal Astronomical Society 424, n. 4 (17 luglio 2012): 2646–58. http://dx.doi.org/10.1111/j.1365-2966.2012.21330.x.

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McLeod, M., J. Aislabie, J. Ryburn, A. McGill e M. Taylor. "Microbial and chemical tracer movement through two Southland soils, New Zealand". Soil Research 41, n. 6 (2003): 1163. http://dx.doi.org/10.1071/sr02149.

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There has been a recent, rapid increase in both land application of dairy shed effluent in Southland, New Zealand, and the microbial load in ground and surface waters. We investigated the fate of faecal coliforms, a host-specific Salmonella bacteriophage, and a non-reactive chemical tracer (Br–), when applied to large intact lysimeter soil cores (500 mm diam. by 500 mm high), to determine the pattern of microbial transport through typical Southland soils. The soils were a poorly drained Fragic Perch-gley Pallic Soil, and a well-drained Typic Firm Brown Soil. A depth of 25 mm of dairy shed effluent containing faecal coliforms and spiked with bacteriophage and Br– was applied to the soil at a rate of 5 mm/h followed by ~1 pore volume of simulated rainfall applied at 5 mm/h. Resulting leachates, collected continuously over ~1 pore volume, were analysed for the microbial and bromide tracers. The microbial tracers moved rapidly through both soils, peaking early in the leachate at ~0.15 pore volume and then tailing off in a pattern indicative of bypass flow. Bromide moved more uniformly through the soils but peaked at ~0.5–0.8 pore volume. The microbial flow pattern observed indicates that the structure in these soils makes them vulnerable to leaching of microbes into local surface and ground water. The large difference between the rate of microbial and chemical tracer transport indicates chemical tracers should only be used with caution to model microbial transport parameters.

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Wu, Xiaokang, Huang Yang, Darryn W. Waugh, Clara Orbe, Simone Tilmes e Jean-Francois Lamarque. "Spatial and temporal variability of interhemispheric transport times". Atmospheric Chemistry and Physics 18, n. 10 (29 maggio 2018): 7439–52. http://dx.doi.org/10.5194/acp-18-7439-2018.

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Abstract. The seasonal and interannual variability of transport times from the northern midlatitude surface into the Southern Hemisphere is examined using simulations of three idealized “age” tracers: an ideal age tracer that yields the mean transit time from northern midlatitudes and two tracers with uniform 50- and 5-day decay. For all tracers the largest seasonal and interannual variability occurs near the surface within the tropics and is generally closely coupled to movement of the Intertropical Convergence Zone (ITCZ). There are, however, notable differences in variability between the different tracers. The largest seasonal and interannual variability in the mean age is generally confined to latitudes spanning the ITCZ, with very weak variability in the southern extratropics. In contrast, for tracers subject to spatially uniform exponential loss the peak variability tends to be south of the ITCZ, and there is a smaller contrast between tropical and extratropical variability. These differences in variability occur because the distribution of transit times from northern midlatitudes is very broad and tracers with more rapid loss are more sensitive to changes in fast transit times than the mean age tracer. These simulations suggest that the seasonal–interannual variability in the southern extratropics of trace gases with predominantly NH midlatitude sources may differ depending on the gases' chemical lifetimes.

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England, Matthew H., e Ernst Maier-Reimer. "Using chemical tracers to assess ocean models". Reviews of Geophysics 39, n. 1 (febbraio 2001): 29–70. http://dx.doi.org/10.1029/1998rg000043.

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Wang, Zhen, Masoume Amirkhani, Suemar A. G. Avelar, Daibin Yang e Alan G. Taylor. "Systemic Uptake of Fluorescent Tracers by Soybean (Glycine max (L.) Merr.) Seed and Seedlings". Agriculture 10, n. 6 (26 giugno 2020): 248. http://dx.doi.org/10.3390/agriculture10060248.

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Systemic seed treatment uptake was investigated in seeds and seedlings using fluorescent tracers to mimic systemic agrochemicals. Soybean was used as the model as soybean has the permeable seed coat characteristic to both charged and noncharged molecules. The purpose of the paper is to (1) screen 32 fluorescent tracers and then use optimal tracers for seed and seedling uptake, (2) investigate varietal differences in seed uptake, (3) examine the distribution of tracer uptake into 14-day-old seedlings, and (4) study the relationship between seed treatment lipophilicity, measured as log P on seed and root uptake. The major chemical families that displayed both seed and seedling uptake were coumarins and xanthenes. Seed uptake of coumarin 120 ranged from 1.1% to 4.8% of the applied seed treatment tracer from 15 yellow-seeded varieties. Rhodamine B, a xanthene compound uptake in seedlings, showed translocation from the applied seed treatment to all seedling tissues. Most of the tracer was measured in the hypocotyl and root, with lesser amounts in the epicotyl and true leaves. Log P is well documented in the literature to model systemic uptake by roots, but log P of the tracers were not related to seed uptake.

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Podglajen, Aurélien, e Felix Ploeger. "Retrieving the age of air spectrum from tracers: principle and method". Atmospheric Chemistry and Physics 19, n. 3 (8 febbraio 2019): 1767–83. http://dx.doi.org/10.5194/acp-19-1767-2019.

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Abstract. Surface-emitted tracers with different dependencies on transit time (e.g., due to chemical loss or time-dependent boundary conditions) carry independent pieces of information on the age of air spectrum (the distribution of transit times from the surface). This paper investigates how and to what extent knowledge of tracer concentrations can be used to retrieve the age spectrum. Since the mixing ratios of the tracers considered depend linearly on the transit time distribution, the question posed can be formulated as a linear inverse problem of small dimension. An inversion methodology is introduced, which does not assume a prescribed shape for the spectrum. The performance of the approach is first evaluated on a constructed set of artificial radioactive tracers derived from idealized spectra. Hereafter, the inversion method is applied to outputs of a chemistry–transport model. The latter experiment highlights the limits of inversions using only parent radioactive tracers: they are unable to retrieve fine-scale structures such as the annual cycle. Improvements can be achieved by including daughter decaying tracers and tracers with an annual cycle at the surface. This study demonstrates the feasibility of retrieving the age spectrum from tracers and has implications for transport diagnosis in models and observations.

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Emmons, L. K., P. G. Hess, J. F. Lamarque e G. G. Pfister. "Tagged ozone mechanism for MOZART-4, CAM-chem, and other chemical transport models". Geoscientific Model Development Discussions 5, n. 3 (24 luglio 2012): 1949–85. http://dx.doi.org/10.5194/gmdd-5-1949-2012.

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Abstract. A procedure for tagging ozone produced from NO sources through updates to an existing chemical mechanism is described, and results from its implementation in the Model for Ozone and Related chemical Tracers (MOZART-4), a global chemical transport model, are presented. Artificial tracers are added to the mechanism, thus not affecting the standard chemistry. The results are linear in the troposphere, i.e., the sum of ozone from individual tagged sources equals the ozone from all sources to within 3% in zonal mean monthly averages. The stratospheric ozone contribution to the troposphere determined from the difference between total ozone and ozone from all tagged sources is significantly less than estimates using a traditional stratospheric ozone tracer (8 vs 20 ppbv at the surface). The commonly used technique of perturbing NO emissions by 20% in a region to determine its ozone contribution is compared to the tagging technique, showing that the tagged ozone is 2–4 times the ozone contribution that was deduced from perturbing emissions.

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Viana, Mar, Fulvio Amato, Andrés Alastuey, Xavier Querol, Teresa Moreno, Saúl García Dos Santos, María Dolores Herce e Rosalía Fernández-Patier. "Chemical Tracers of Particulate Emissions from Commercial Shipping". Environmental Science & Technology 43, n. 19 (ottobre 2009): 7472–77. http://dx.doi.org/10.1021/es901558t.

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Viti, Serena, e Estelle Bayet. "Chemical tracers of dense gas in extragalactic environments". Proceedings of the International Astronomical Union 5, H15 (novembre 2009): 413. http://dx.doi.org/10.1017/s174392131001001x.

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Ferro, A. Arellano, L. Parrao e L. Mantegazza. "Supergiant Stars as Tracers of Galactic Chemical Composition". Symposium - International Astronomical Union 164 (1995): 366. http://dx.doi.org/10.1017/s007418090010885x.

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A photometric reddening-free calibration for [Fe/H] valid for giant and supergiant stars of intermediate temperature, has been obtained using the Strömgren uvbyß system. Galactic supergiants, supergiants in Magellanic Clouds and galactic metal deficient red giants with spectroscopic determinations of [Fe/H] were used as calibrators. The calibration can be used to predict [Fe/H] with an accuracy of 0.33 dex and shows the potential of supergiant stars as tracers of iron abundances in other galaxies.

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Fortenberry, Robert, Pearson Suniga, Mojdeh Delshad, Bharat Singh, Hassan A. AlKaaoud, Charlie T. Carlisle e Gary A. Pope. "Design and Demonstration of New Single-Well Tracer Test for Viscous Chemical Enhanced-Oil-Recovery Fluids". SPE Journal 21, n. 04 (15 agosto 2016): 1075–85. http://dx.doi.org/10.2118/178914-pa.

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Summary Single-well-partitioning-tracer tests (SWTTs) are used to measure the saturation of oil or water near a wellbore. If used before and after injection of enhanced-oil-recovery (EOR) fluids, they can evaluate EOR flood performance in a so-called one-spot pilot. Four alkaline/surfactant/polymer (ASP) one-spot pilots were recently completed in Kuwait's Sabriyah-Mauddud (SAMA) reservoir, a thick, heterogeneous carbonate operated by Kuwait Oil Company (KOC). UTCHEM (Delshad et al. 2013), the University of Texas chemical-flooding reservoir simulator, was used to interpret results of two of these one-spot pilots performed in an unconfined zone within the thick SAMA formation. These simulations were used to design a new method for injecting partitioning tracers for one-spot pilots. The recommended practice is to inject the tracers into a relatively uniform confined zone, but, as seen in this work, that is not always possible, so an alternative design was needed to improve the accuracy of the test. The simulations showed that there was a flow-conformance problem when the partitioning tracers were injected into a perforated zone without confinement after the viscous ASP and polymer-drive solutions. The water-conveyed-tracer solutions were being partially diverted outside of the ASP-swept zone where they contacted unswept oil. Because of this problem, the initial interpretation of the performance of the chemicals was pessimistic, overestimating the chemical residual oil saturation (ROS) by up to 12 saturation units. Additional simulations indicated that the oil saturation in the ASP-swept zone could be properly estimated by avoiding the post-ASP waterflood and injecting the post-ASP tracers in a viscous polymer solution rather than in water. An ASP one-spot pilot using the new SWTT design resulted in an estimated ROS of only 0.06 after injection of chemicals (Carlisle et al. 2014). These saturation values were obtained by history matching tracer-production data by use of both traditional continuously-stirred-tank (CSTR) models and compositional, reactive-transport reservoir models. The ability of the simulator to model every phase of the one-spot pilot operation was crucial to the insight of modified SWTT design. The waterflood, first SWTT, ASP flood, and the final SWTT were simulated using a heterogeneous permeability field representative of the Mauddud formation. Laboratory data, field-ASP quality-control information, and injection strategy were all accounted for in these simulations. We describe the models, how they were used, and how the results were used to modify the SWTT design. We further discuss the implications for other SWTTs. The advantage of mechanistic simulation of multiple aspects of a one-spot pilot is an important theme of this study. Because the pore space investigated by the SWTTs can be affected by the previously injected EOR fluids (and vice versa), these interactions should be accounted for. This simulation approach can be used to identify and mitigate design problems during each phase of a challenging one-spot pilot.

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Yamamoto, Satoshi, Yoko Oya e Nami Sakai. "Chemical Tracers of Dynamics in Low-Mass Protostellar Objects". Proceedings of the International Astronomical Union 13, S332 (marzo 2017): 175–86. http://dx.doi.org/10.1017/s174392131700761x.

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AbstractRecent progress in astrochemistry of low-mass protostellar sources is reviewed. In particular, we focus on disk formation processes and associated chemical changes at a 50 au scale, which is extensively being studied with ALMA. A small scale chemical differentiation sensitively reflects changes in physical conditions, and hence, it provides us with unique opportunities of chemical diagnostics of disk-forming regions. Complex physical and chemical pictures of disk formation revealed by observations are summarized, and future prospects are discussed.

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Pan, L. L., A. Kunz, C. R. Homeyer, L. A. Munchak, D. E. Kinnison e S. Tilmes. "Commentary on using equivalent latitude in the upper troposphere and lower stratosphere". Atmospheric Chemistry and Physics Discussions 11, n. 12 (15 dicembre 2011): 33095–126. http://dx.doi.org/10.5194/acpd-11-33095-2011.

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Abstract. We discuss the use of potential vorticity (PV) based equivalent latitude (EqLat) and potential temperature (θ) coordinates in the upper troposphere and lower stratosphere (UTLS) for chemical transport studies. The main objective is to provide a cautionary note on using EqLat–θ coordinates for aggregating chemical tracers in the UTLS. Several examples are used to show 3-D distributions of EqLat together with chemical constituents for a range of θ. We show that the use of PV–θ coordinates may not be suitable for several reasons when tropospheric processes are an important part of a study. Due to the different static stability structures between the stratosphere and troposphere, the use of θ as a vertical coordinate does not provide equal representations of the UT and LS. Since the θ surfaces are often quasi-vertical in the troposphere, the θ coordinate does not work well distinguishing the UT from the boundary layer. We further discuss the duality of PV/EqLat as a tracer versus as a coordinate variable. Using an example, we show that while PV/EqLat serves well as a transport tracer in the UTLS region, it may misrepresent the effect of transport when used as a coordinate to average chemical tracers. Overall, when choosing these coordinates, considerations need to be made not only based on the time scale of PV being a conservative tracer, but also the specific research questions to be addressed.

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Pan, L. L., A. Kunz, C. R. Homeyer, L. A. Munchak, D. E. Kinnison e S. Tilmes. "Commentary on using equivalent latitude in the upper troposphere and lower stratosphere". Atmospheric Chemistry and Physics 12, n. 19 (11 ottobre 2012): 9187–99. http://dx.doi.org/10.5194/acp-12-9187-2012.

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Abstract. We discuss the use of potential vorticity (PV) based equivalent latitude (EqLat) and potential temperature (θ) coordinates in the upper troposphere and lower stratosphere (UTLS) for chemical transport studies. The main objective is to provide a cautionary note on using EqLat-θ coordinates for aggregating chemical tracers in the UTLS. Several examples are used to show 3-D distributions of EqLat together with chemical constituents for a range of θ. We show that the use of PV-θ coordinates may not be suitable for several reasons when tropospheric processes are an important part of a study. Due to the different static stability structures between the stratosphere and troposphere, the use of θ as a vertical coordinate does not provide equal representations of the UT and LS. Since the θ surfaces in the troposphere often intersect the surface of the Earth, the θ variable does not work well distinguishing the UT from the boundary layer when used globally as a vertical coordinate. We further discuss the duality of PV/EqLat as a tracer versus as a coordinate variable. Using an example, we show that while PV/EqLat serves well as a transport tracer in the UTLS region, it may conceal the chemical structure associated with wave breaking when used as a coordinate to average chemical tracers. Overall, when choosing these coordinates, considerations need to be made not only based on the time scale of PV being a conservative tracer, but also the specific research questions to be addressed.

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Cabeçadas, Graça, Maria J. Brogueira e Célia Gonçalves. "Intermediate water masses off south-southwest Portugal: Chemical tracers". Journal of Marine Research 61, n. 4 (1 luglio 2003): 539–52. http://dx.doi.org/10.1357/002224003322384924.

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Visser, Ruud, Edwin A. Bergin e Jes K. Jørgensen. "Chemical tracers of episodic accretion in low-mass protostars". Astronomy & Astrophysics 577 (maggio 2015): A102. http://dx.doi.org/10.1051/0004-6361/201425365.

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Sestito, P., A. Bragaglia, S. Randich, R. Pallavicini, S. M. Andrievsky e S. A. Korotin. "Open clusters as key tracers of Galactic chemical evolution". Astronomy & Astrophysics 488, n. 3 (9 luglio 2008): 943–58. http://dx.doi.org/10.1051/0004-6361:200809650.

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Hernández, Luis G., Javier García Pérez e Marcela Gaytán-Martínez. "Tracers used in granular systems: Review". Powder Technology 340 (dicembre 2018): 274–89. http://dx.doi.org/10.1016/j.powtec.2018.09.025.

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Pitari, Giovanni, e Eva Mancini. "Impact of future supersonic aircraft on the distribution of stratospheric tracers: Chemical and dynamical perturbations". Meteorologische Zeitschrift 11, n. 3 (2 agosto 2002): 215–23. http://dx.doi.org/10.1127/0941-2948/2002/0011-0215.

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Bron, Emeric, Evelyne Roueff, Maryvonne Gerin, Jérôme Pety, Pierre Gratier, Franck Le Petit, Viviana Guzman et al. "Tracers of the ionization fraction in dense and translucent gas". Astronomy & Astrophysics 645 (23 dicembre 2020): A28. http://dx.doi.org/10.1051/0004-6361/202038040.

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Context. The ionization fraction in the neutral interstellar medium (ISM) plays a key role in the physics and chemistry of the ISM, from controlling the coupling of the gas to the magnetic field to allowing fast ion-neutral reactions that drive interstellar chemistry. Most estimations of the ionization fraction have relied on deuterated species such as DCO+, whose detection is limited to dense cores representing an extremely small fraction of the volume of the giant molecular clouds that they are part of. As large field-of-view hyperspectral maps become available, new tracers may be found. The growth of observational datasets is paralleled by the growth of massive modeling datasets and new methods need to be devised to exploit the wealth of information they contain. Aims. We search for the best observable tracers of the ionization fraction based on a grid of astrochemical models, with the broader aim of finding a general automated method applicable to searching for tracers of any unobservable quantity based on grids of models. Methods. We built grids of models that randomly sample a large range of physical conditions (unobservable quantities such as gas density, temperature, elemental abundances, etc.) and computed the corresponding observables (line intensities, column densities) and the ionization fraction. We estimated the predictive power of each potential tracer by training a random forest model to predict the ionization fraction from that tracer, based on these model grids. Results. In both translucent medium and cold dense medium conditions, we found several observable tracers with very good predictive power for the ionization fraction. Many tracers in cold dense medium conditions are found to be better and more widely applicable than the traditional DCO+/HCO+ ratio. We also provide simpler analytical fits for estimating the ionization fraction from the best tracers, and for estimating the associated uncertainties. We discuss the limitations of the present study and select a few recommended tracers in both types of conditions. Conclusions. The method presented here is very general and can be applied to the measurement of any other quantity of interest (cosmic ray flux, elemental abundances, etc.) from any type of model (PDR models, time-dependent chemical models, etc.).

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Semenov, Mikhail Y., Yuri M. Semenov, Anton V. Silaev e Larisa A. Begunova. "Source Apportionment of Inorganic Solutes in Surface Waters of Lake Baikal Watershed". Sustainability 13, n. 10 (12 maggio 2021): 5389. http://dx.doi.org/10.3390/su13105389.

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The aim of this study was to obtain a detailed picture of the origin of the anthropogenic and natural inorganic solutes in the surface waters of the Lake Baikal watershed using limited data on solute sources. To reveal the origin of solutes, the chemical composition of water was considered as a mixture of solutes from different sources such as rocks and anthropogenic wastes. The end-member mixing approach (EMMA), based on the observation that the element ratios in water uncorrelated with one another are those that exhibit differences in values across the different types of rocks and anthropogenic wastes, was used for source apportionment. According to the results of correlation analysis, two tracers of sources of most abundant ions present in riverine waters were selected. The first tracer was the ratio of combined concentration of calcium and magnesium ions to concentration of potassium ion ((Ca2+ + Mg2+)/K+), and the second tracer was the ratio of sulfate and bicarbonate ion concentrations (SO42−/HCO3−). Using these tracers, three sources of main ions in water, such as sulfide-bearing silicate rocks, non-sulfide silicate rocks and carbonate rocks, were apportioned. The results of cluster analysis showed the possibility of using the ratios of strontium, iron, manganese, molybdenum, nickel, and vanadium concentrations (Sr/Fe, Sr/Mn, Ni/V, Mo/V) as tracers of the trace element sources. The use of these tracers and the obtained data on sources of main ions showed the possibility of identifying the natural trace element sources and distinguishing between natural and anthropogenic trace element sources.

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Wan, Xin, Shichang Kang, Maheswar Rupakheti, Qianggong Zhang, Lekhendra Tripathee, Junming Guo, Pengfei Chen et al. "Molecular characterization of organic aerosols in the Kathmandu Valley, Nepal: insights into primary and secondary sources". Atmospheric Chemistry and Physics 19, n. 5 (4 marzo 2019): 2725–47. http://dx.doi.org/10.5194/acp-19-2725-2019.

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Abstract. Organic atmospheric aerosols in the Hindu Kush–Himalayas–Tibetan Plateau region are still poorly characterized. To better understand the chemical characteristics and sources of organic aerosols in the foothill region of the central Himalaya, the atmospheric aerosol samples were collected in Bode, a suburban site of the Kathmandu Valley (KV) over a 1-year period from April 2013 to April 2014. Various molecular tracers from specific sources of primary organic aerosols (POAs) and secondary organic aerosols (SOAs) were determined. Tracer-based estimation methods were employed to apportion contributions from each source. The concentrations of organic carbon (OC) and elemental carbon (EC) increased during winter with a maximum monthly average in January. Levoglucosan (a molecular tracer for biomass burning, BB) was observed as the dominant species among all the analyzed organic tracers and its annual average concentration was 788±685 ng m−3 (ranging from 58.8 to 3079 ng m−3). Isoprene-SOA (I-SOA) represented a high concentration among biogenic-SOA tracers. For the seasonality, anhydrosugars, phenolic compounds, resin acid, and aromatic SOA tracer showed similar seasonal variations with OC and EC while monosaccharides, sugar alcohols, and I-SOA tracers showed lower levels during winter. BB contributed a significant fraction to OC, averaging 24.9 %±10.4 % during the whole year, and up to 36.3 %±10.4 % in the post-monsoon season. On an annual average basis, anthropogenic toluene-derived secondary OC accounted for 8.8 % and biogenic secondary OC contributed 6.2 % to total OC. The annual contribution of fungal spores to OC was 3.2 % with a maximum during the monsoon season (5.9 %). For plant debris, it accounted for 1.4 % of OC during the monsoon. Therefore, OC is mainly associated with BB and other anthropogenic activity in the KV. Our findings are conducive to designing effective measures to mitigate the heavy air pollution and its impacts in the KV and surrounding area.

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27

Patrick, Lee R., Chris J. Evans, Ben Davies, Rolf-Peter Kudritzki, Maria Bergemann e Annette N. M. Ferguson. "Red Supergiants as Chemical Abundance Probes: The Local Group dwarf NGC6822". Proceedings of the International Astronomical Union 14, S344 (agosto 2018): 213–16. http://dx.doi.org/10.1017/s174392131800649x.

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AbstractRed Supergiant Stars (RSGs) are important probes of stellar and chemical evolution in star-forming environments. They represent the brightest near-IR stellar components of external galaxies and probe the most recent stellar population to provide robust, independent abundance estimates. The Local Group dwarf irregular galaxy, NGC6822, is a reasonably isolated galaxy with an interesting structure and turbulent history. Using RSGs as chemical abundance probes, we estimate metallicities in the central region of NGC6822, finding a suggestion of a metallicity gradient (in broad agreement with nebular tracers), however, this requires further study for confirmation. With intermediate resolution Multi-object spectroscopy (from e.g. KMOS, EMIR, MOSFIRE) combined with state-of-the-art stellar model atmospheres, we demonstrate how RSGs can be used to estimate stellar abundances in external galaxies. In this context, we compare stellar and nebular abundance tracers in NGC 6822 and by combining stellar and nebular tracers we estimate an abundance gradient of −0.18 ± 0.05 dex/kpc.

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28

Emmons, L. K., P. G. Hess, J. F. Lamarque e G. G. Pfister. "Tagged ozone mechanism for MOZART-4, CAM-chem and other chemical transport models". Geoscientific Model Development 5, n. 6 (6 dicembre 2012): 1531–42. http://dx.doi.org/10.5194/gmd-5-1531-2012.

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Abstract. A procedure for tagging ozone produced from NO sources through updates to an existing chemical mechanism is described, and results from its implementation in the Model for Ozone and Related chemical Tracers (MOZART-4), a global chemical transport model, are presented. Artificial tracers are added to the mechanism, thus, not affecting the standard chemistry. The results are linear in the troposphere, i.e., the sum of ozone from individual tagged sources equals the ozone from all sources to within 3% in zonal mean monthly averages. In addition, the tagged ozone is shown to equal the standard ozone, when all tropospheric sources are tagged and stratospheric input is turned off. The stratospheric ozone contribution to the troposphere determined from the difference between total ozone and ozone from all tagged sources is significantly less than estimates using a traditional stratospheric ozone tracer (8 vs. 20 ppbv at the surface). The commonly used technique of perturbing NO emissions by 20% in a region to determine its ozone contribution is compared to the tagging technique, showing that the tagged ozone is 2–4 times the ozone contribution that was deduced from perturbing emissions. The ozone tagging described here is useful for identifying source contributions based on NO emissions in a given state of the atmosphere, such as for quantifying the ozone budget.

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29

Lu, Dawei, Jihua Tan, Xuezhi Yang, Xu Sun, Qian Liu e Guibin Jiang. "Unraveling the role of silicon in atmospheric aerosol secondary formation: a new conservative tracer for aerosol chemistry". Atmospheric Chemistry and Physics 19, n. 5 (5 marzo 2019): 2861–70. http://dx.doi.org/10.5194/acp-19-2861-2019.

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Abstract. Aerosol particles are ubiquitous in the atmosphere and affect the quality of human life through their climatic and health effects. The formation and growth of aerosol particles involve extremely complex reactions and processes. Due to limited research tools, the sources and chemistry of aerosols are still not fully understood, and until now have normally been investigated by using chemical species of secondary aerosols (e.g., NH4+, NO3-, SO42-, SOC) as tracers. Here we investigated the role of silicon (Si), an ubiquitous but relatively inert element, during the secondary aerosol formation process. We analyzed the correlation of Si in airborne fine particles (PM2.5) collected in Beijing – a typical pollution region – with the secondary chemical species and secondary particle precursors (e.g., SO2 and NOx). The total mass of Si in PM2.5 was found to be uncorrelated with the secondary aerosol formation process, which suggested that Si is a new conservative tracer for the amount of primary materials in PM2.5 and can be used to estimate the relative amount of secondary and primary compounds in PM2.5. This finding enables the accurate estimation of secondary aerosol contribution to PM2.5 by using Si as a single tracer rather than the commonly used multiple chemical tracers. In addition, we show that the correlation analysis of secondary aerosols with the Si isotopic composition of PM2.5 can further reveal the sources of the precursors of secondary aerosols. Therefore, Si may provide a new tool for aerosol chemistry studies.

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30

Carpenter, Chris. "Lessons From 10 Years of Monitoring With Chemical Inflow Tracers". Journal of Petroleum Technology 70, n. 09 (1 settembre 2018): 81–83. http://dx.doi.org/10.2118/0918-0081-jpt.

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31

McCall, Marshall L., e Michael G. Richer. "Planetary Nebulae as Tracers of Chemical Evolution in External Galaxies". Symposium - International Astronomical Union 209 (2003): 583–92. http://dx.doi.org/10.1017/s0074180900209790.

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Abstract (sommario):

Thanks to recent advances in instrumentation, metal abundances now can be measured routinely for PNe situated in galaxies beyond the Magellanic Clouds. Consequently, PNe are becoming a valuable tool for studying the chemical evolution of external galaxies, especially those which are not forming stars. Here we review problems and progress in this exciting nascent field of interdisciplinary research.

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32

Limburg, Karin E. "Anomalous migrations of anadromous herrings revealed with natural chemical tracers". Canadian Journal of Fisheries and Aquatic Sciences 55, n. 2 (1 febbraio 1998): 431–37. http://dx.doi.org/10.1139/f97-219.

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Abstract (sommario):

Anadromous herrings of the genus Alosa are generally thought to leave their natal river or estuary at the end of the first growing season and return as mature adults to spawn. Nevertheless, immature yearling alosines have been observed in large numbers in the Hudson River estuary during and after the spring spawning run. I analyzed the stable isotopic ( delta 13C, delta 15N) compositions of 26 blueback herring (Alosa aestivalis), eight American shad (Alosa sapidissima), and 10 alewife (Alosa pseudoharengus) collected from 55-225 km above the estuary mouth during April-July and compared them with isotopic compositions of young-of-year (resident) alosines, as well as adults (marine phase). delta 13C of the May-caught American shad and alewife indicated a marine origin (greater than -22.5omicron); blueback herring split into both marine and freshwater ( delta 13C less than -25.5omicron) groups. June-caught fish had intermediate values. Microprobe traces of Sr in these fishes' otoliths helped further to discriminate between resident fishes and those that had migrated to sea (or brackish water) and then moved back upriver for a period of several weeks. The combination of biogeochemical tracer methods holds promise for elucidating complex life histories of fishes and helps to pose questions about plasticity of migration.

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33

Sestito, P., A. Bragaglia, S. Randich, E. Carretta, L. Prisinzano e M. Tosi. "Old open clusters as key tracers of Galactic chemical evolution". Astronomy & Astrophysics 458, n. 1 (ottobre 2006): 121–34. http://dx.doi.org/10.1051/0004-6361:20065175.

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34

Lu, Rong, Chichung Lin, Richard Turco e Akio Arakawa. "Cumulus transport of chemical tracers: 1. Cloud-resolving model simulations". Journal of Geophysical Research: Atmospheres 105, n. D8 (1 aprile 2000): 10001–21. http://dx.doi.org/10.1029/2000jd900009.

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35

Subramanian, S. K., Yan Li e L. M. Cathles. "Assessing preferential flow by simultaneously injecting nanoparticle and chemical tracers". Water Resources Research 49, n. 1 (gennaio 2013): 29–42. http://dx.doi.org/10.1029/2012wr012148.

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36

Bragaglia, A., P. Sestito, S. Villanova, E. Carretta, S. Randich e M. Tosi. "Old open clusters as key tracers of Galactic chemical evolution". Astronomy & Astrophysics 480, n. 1 (9 gennaio 2008): 79–90. http://dx.doi.org/10.1051/0004-6361:20077904.

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37

Ellinger, Y., M. Lattelais, F. Pauzat, J.-C. Guillemin e B. Zanda. "Meteoritic amino acids as chemical tracers of parent-body chemistries". Monthly Notices of the Royal Astronomical Society 502, n. 3 (1 febbraio 2021): 4064–73. http://dx.doi.org/10.1093/mnras/stab217.

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ABSTRACT The analysis of the organic matter of meteorites made it possible to identify over 70 amino acids (AA), including 8 of those found in living organisms. However, their relative abundances vary drastically with the type of the carbonaceous chondrite, even for isomers of same chemical formula. In this report, we address the question whether this difference may have its origin in the relative stability of these isomers according to the conditions they experienced when they were formed and after. To this end, we rely on the fact that for most of the species observed so far in the interstellar medium (ISM), the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle, MEP). Using quantum density functional theory (DFT) simulations, we investigate the relative stability of the lowest energy isomers of alanine (Ala) and amino butyric acid (ABA) in the neutral, protonated, and zwitterionic structures together with corresponding nitrile precursors. It is shown that β-alanine and γ-ABA are the most stable in a protonated form, whereas α-AA are the most stable in the zwitterionic and nitrile structures. The different composition of the carbonaceous chondrites CIs and CMs could be linked to the chemical context of the aqueous alterations of the parent bodies.

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38

Orr, James C., Raymond G. Najjar, Olivier Aumont, Laurent Bopp, John L. Bullister, Gokhan Danabasoglu, Scott C. Doney et al. "Biogeochemical protocols and diagnostics for the CMIP6 Ocean Model Intercomparison Project (OMIP)". Geoscientific Model Development 10, n. 6 (9 giugno 2017): 2169–99. http://dx.doi.org/10.5194/gmd-10-2169-2017.

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Abstract. The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP's biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948–2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, CTabio and 14CTabio, to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols are founded on those from previous phases of the Ocean Carbon-Cycle Model Intercomparison Project. They have been merged and updated to reflect improvements concerning gas exchange, carbonate chemistry, and new data for initial conditions and atmospheric gas histories. Code is provided to facilitate their implementation.

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39

Li, Jiamin, Xiaoping Chen, Jiliang Ma e Cai Liang. "A method for measuring the residence time distribution of particles in a fluidized bed based on digital image analysis". International Journal of Chemical Reactor Engineering 19, n. 1 (1 gennaio 2021): 63–73. http://dx.doi.org/10.1515/ijcre-2020-0177.

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Abstract Traditional methods for measuring the residence time distribution (RTD) of particles in a fluidized bed are complex and time-consuming. To this regard, the present work proposes a new measurement method with remarkable efficiency based on digital image analysis. The dyed tracers are recognized in the images of the samples due to the difference of colors from bed materials. The HSV and the well-known RGB color space were employed to distinguish the tracers. By enhancing the Saturation and the Value in HSV and adjusting the gray range of images, the recognition error is effectively reduced. Then the pixels representing the tracers are distinguished, based on which the concentration of the tracers and RTD are measured. The efficiency, accuracy and repeatability of the method were validated by RTD measurements experiments. The method is also fit for distinguishing the target particles from multi-component systems consisting of particles of different colors.

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40

Liu, Peng, Christian Hogrefe, Ulas Im, Jesper H. Christensen, Johannes Bieser, Uarporn Nopmongcol, Greg Yarwood, Rohit Mathur, Shawn Roselle e Tanya Spero. "Attributing differences in the fate of lateral boundary ozone in AQMEII3 models to physical process representations". Atmospheric Chemistry and Physics 18, n. 23 (5 dicembre 2018): 17157–75. http://dx.doi.org/10.5194/acp-18-17157-2018.

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Abstract. Increasing emphasis has been placed on characterizing the contributions and the uncertainties of ozone imported from outside the US. In chemical transport models (CTMs), the ozone transported through lateral boundaries (referred to as LB ozone hereafter) undergoes a series of physical and chemical processes in CTMs, which are important sources of the uncertainty in estimating the impact of LB ozone on ozone levels at the surface. By implementing inert tracers for LB ozone, the study seeks to better understand how differing representations of physical processes in regional CTMs may lead to differences in the simulated LB ozone that eventually reaches the surface across the US. For all the simulations in this study (including WRF∕CMAQ, WRF∕CAMx, COSMO-CLM∕CMAQ, and WRF∕DEHM), three chemically inert tracers that generally represent the altitude ranges of the planetary boundary layer (BC1), free troposphere (BC2), and upper troposphere–lower stratosphere (BC3) are tracked to assess the simulated impact of LB specification. Comparing WRF∕CAMx with WRF∕CMAQ, their differences in vertical grid structure explain 10 %–60 % of their seasonally averaged differences in inert tracers at the surface. Vertical turbulent mixing is the primary contributor to the remaining differences in inert tracers across the US in all seasons. Stronger vertical mixing in WRF∕CAMx brings more BC2 downward, leading to higher BCT (BCT=BC1+BC2+BC3) and BC2∕BCT at the surface in WRF∕CAMx. Meanwhile, the differences in inert tracers due to vertical mixing are partially counteracted by their difference in sub-grid cloud mixing over the southeastern US and the Gulf Coast region during summer. The process of dry deposition adds extra gradients to the spatial distribution of the differences in DM8A BCT by 5–10 ppb during winter and summer. COSMO-CLM∕CMAQ and WRF∕CMAQ show similar performance in inert tracers both at the surface and aloft through most seasons, which suggests similarity between the two models at process level. The largest difference is found in summer. Sub-grid cloud mixing plays a primary role in their differences in inert tracers over the southeastern US and the oceans in summer. Our analysis of the vertical profiles of inert tracers also suggests that the model differences in dry deposition over certain regions are offset by the model differences in vertical turbulent mixing, leading to small differences in inert tracers at the surface in these regions.

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41

Magrini, Laura, Letizia Stanghellini e Denise R. Gonçalves. "Extragalactic planetary nebulae: Tracers of the chemical evolution of nearby galaxies". Proceedings of the International Astronomical Union 7, S283 (luglio 2011): 251–58. http://dx.doi.org/10.1017/s1743921312011040.

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AbstractThe study of the chemical composition of Planetary Nebulae in external galaxies is of paramount importance for the fields of stellar evolution and chemical enrichment history of galaxies. In recent years a number of spectroscopic studies with 6-8m-class telescopes have been devoted to this subject improving our knowledge of, among other, the time-evolution of the radial metallicity gradient in disk galaxies, the chemical evolution of dwarf galaxies, and stellar evolution at low metallicity.

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42

Bailey, J. D., J. D. Landstreet e S. Bagnulo. "Discovery of Secular Evolution of the Atmospheric Abundances of Ap Stars". Proceedings of the International Astronomical Union 9, S307 (giugno 2014): 365–66. http://dx.doi.org/10.1017/s1743921314007091.

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AbstractThe stars of the middle main-sequence have relatively quiescent outer layers, and unusual chemical abundance patterns may develop in their atmospheres, revealing the action of such subsurface phenomena as gravitational settling and radiatively driven levitation of trace elements, and their competition with mixing processes such as turbulent diffusion. We report the discovery of the time evolution of such chemical tracers through the main-sequence lifetime of magnetic chemically peculiar stars.

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43

Pozzer, A., P. Jöckel, R. Sander, J. Williams, L. Ganzeveld e J. Lelieveld. "Technical Note: The MESSy-submodel AIRSEA calculating the air-sea exchange of chemical species". Atmospheric Chemistry and Physics 6, n. 12 (5 dicembre 2006): 5435–44. http://dx.doi.org/10.5194/acp-6-5435-2006.

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Abstract (sommario):

Abstract. The new submodel AIRSEA for the Modular Earth Submodel System (MESSy) is presented. It calculates the exchange of chemical species between the ocean and the atmosphere with a focus on organic compounds. The submodel can be easily extended to a large number of tracers, including highly soluble ones. It is demonstrated that the application of explicitly calculated air-sea exchanges with AIRSEA can induce substantial changes in the simulated tracer distributions in the troposphere in comparison to a model setup in which this process is neglected. For example, the simulations of acetone, constrained with measured oceanic concentrations, shows relative changes in the atmospheric surface layer mixing ratios over the Atlantic Ocean of up to 300%.

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44

Pozzer, A., P. Jöckel, R. Sander, L. Ganzeveld e J. Lelieveld. "Technical note: The MESSy-submodel AIRSEA calculating the air-sea exchange of chemical species". Atmospheric Chemistry and Physics Discussions 6, n. 4 (29 agosto 2006): 8189–214. http://dx.doi.org/10.5194/acpd-6-8189-2006.

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Abstract (sommario):

Abstract. The new submodel AIRSEA for the Modular Earth Submodel System (MESSy) is presented. It calculates the exchange of chemical species between the ocean and the atmosphere with a focus on organic compounds. The submodel can be easily extended to a large number of tracers, including highly soluble ones. It is demonstrated that application of explicitly calculated air-sea exchanges with AIRSEA can induce substantial changes in the simulated tracer distributions in the troposphere in comparison to a model version in which this process is neglected. For example, the simulations of acetone, constrained with measured oceanic concentrations, shows relative changes in the atmospheric surface layer mixing ratios over the Atlantic Ocean up to 300%.

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45

Hygate, Alexander P. S., J. M. Diederik Kruijssen, Mélanie Chevance, Andreas Schruba, Daniel T. Haydon e Steven N. Longmore. "An uncertainty principle for star formation – IV. On the nature and filtering of diffuse emission". Monthly Notices of the Royal Astronomical Society 488, n. 2 (25 luglio 2019): 2800–2824. http://dx.doi.org/10.1093/mnras/stz1779.

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Abstract (sommario):

Abstract Diffuse emission is observed in galaxies in many tracers across the electromagnetic spectrum, including tracers of star formation, such as H α and ultraviolet (UV), and tracers of gas mass, such as carbon monoxide (CO) transition lines and the 21-cm line of atomic hydrogen (H i). Its treatment is key to extracting meaningful information from observations such as cloud-scale star formation rates. Finally, studying diffuse emission can reveal information about the physical processes taking place in the interstellar medium, such as chemical transitions and the nature of stellar feedback (through the photon escape fraction). We present a physically motivated method for decomposing astronomical images containing both diffuse emission and compact regions of interest, such as H ii regions or molecular clouds, into diffuse and compact component images through filtering in Fourier space. We have previously presented a statistical method for constraining the evolutionary timeline of star formation and mean separation length between compact star-forming regions with galaxy-scale observations. We demonstrate how these measurements are biased by the presence of diffuse emission in tracer maps and that by using the mean separation length as a critical length-scale to separate diffuse emission from compact emission, we are able to remove its biasing effect. Furthermore, this method provides, without the need for interferometry or ancillary spectral data, a measurement of the diffuse emission fraction in input tracer maps and decomposed diffuse and compact emission maps for further analysis.

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46

Ginot, Patrick, Margit Schwikowski, Ulrich Schotterer, Willibald Stichler, Heinz W. Gäggeler, Bernard Francou, Robert Gallaire e Bernard Pouyaud. "Potential for climate variability reconstruction from Andean glaciochemical records". Annals of Glaciology 35 (2002): 443–50. http://dx.doi.org/10.3189/172756402781816618.

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Abstract (sommario):

AbstractIn order to select glacier sites suitable for the reconstruction of short-term climate variability, chemical constituents of shallow cores from Chimborazo, Ecuador, Illimani, Bolivia, and Cerro Tapado, Chile, were analyzed to determine if they represent the climate and atmospheric conditions of the particular area. Pronounced variations were observed in the Chimborazo core, which were attributed to the seasonal occurrence of wet and dry periods. Using chemical tracers, the Pacific and the Amazon basin were identified as the two principal sources of atmospheric moisture. In the Illimani record, seasonality is obvious but is less regular than in the Chimborazo core. Chemical tracers point to the Amazon basin as a moisture source. Post-depositional sublimation masks a possible atmospheric signal in the glaciochemical records from Cerro Tapado. the arid conditions and a prevailing high condensation level also cause little variability in the stable-isotope content. Irregular, more negative δ18O values occur during the humid phases of El Niño events. Despite alterations due to sublimation, chemical tracers indicate the Pacific Ocean as a main moisture source for precipitation preserved on Glaciar CerroTapado.

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47

Semenov, Mikhail Yu, Anton V. Silaev, Yuri M. Semenov e Larisa A. Begunova. "Using Si, Al and Fe as Tracers for Source Apportionment of Air Pollutants in Lake Baikal Snowpack". Sustainability 12, n. 8 (22 aprile 2020): 3392. http://dx.doi.org/10.3390/su12083392.

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Abstract (sommario):

The aim of this study was to select chemical species characterized by distinctly different proportions in natural and anthropogenic particulate matter that could be used as tracers for air pollutant sources. The end-member mixing approach, based on the observation that the chemical species in snow closely correlated with land use are those that exhibit differences in concentrations across the different types of anthropogenic wastes, was used for source apportionment. The concentrations of Si and Fe normalized to Al were used as tracers in the mixing equations. Mixing diagrams showed that the major pollution sources (in descending order) are oil, coal, and wood combustion. The traces of several minor sources, such as aluminum production plants, pulp and paper mills, steel rust, and natural aluminosilicates, were also detected. It was found that the fingerprint of diesel engines on snow is similar to that of oil combustion; thus, future research of the role of diesel engines in air pollution will be needed. The insufficient precision of source apportionment is probably due to different combinations of pollution sources in different areas. Thus, principles for the delineation of areas affected by different source combinations should be the subject of further studies.

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48

Hoyle, C. R., V. Marécal, M. R. Russo, G. Allen, J. Arteta, C. Chemel, M. P. Chipperfield et al. "Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport". Atmospheric Chemistry and Physics 11, n. 15 (9 agosto 2011): 8103–31. http://dx.doi.org/10.5194/acp-11-8103-2011.

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Abstract (sommario):

Abstract. The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.

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49

Vorkas, C. A., e B. J. Lloyd. "A comparative assessment of bacteriophages as tracers and models for virus removal waste stabilisation ponds". Water Science and Technology 42, n. 10-11 (1 novembre 2000): 127–38. http://dx.doi.org/10.2166/wst.2000.0625.

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Abstract (sommario):

The suitability of five strains of bacteriophage as hydraulic tracers and as models of pathogenic virus removal in waste stabilisation ponds was determined in vitro. The bacteriophages investigated included Serratia marcescens, Pseudomonas syringae, Erwinia amanas, and two phages of Erwinia amylovora. The study modeled the survival of these bacteriophages under the physico-chemical conditions typically encountered in WSP systems. This demonstrated that the selected phages, were greatly affected by increased pH and sunlight, but survived for sufficient time at moderate pH levels (6.5-8.5) to justify their use as tracers in full-scale WSPs. Furthermore, their survival/removal in adjusted physico-chemical conditions, suspended solids concentration and temperature, was comparable to human pathogenic viruses. It was concluded that these phages are potentially useful tracers and indicators for pathogenic viruses in WSPs.

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50

Griffin, Debora, Kaley A. Walker, Ingo Wohltmann, Sandip S. Dhomse, Markus Rex, Martyn P. Chipperfield, Wuhu Feng, Gloria L. Manney, Jane Liu e David Tarasick. "Stratospheric ozone loss in the Arctic winters between 2005 and 2013 derived with ACE-FTS measurements". Atmospheric Chemistry and Physics 19, n. 1 (16 gennaio 2019): 577–601. http://dx.doi.org/10.5194/acp-19-577-2019.

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Abstract (sommario):

Abstract. Stratospheric ozone loss inside the Arctic polar vortex for the winters between 2004–2005 and 2012–2013 has been quantified using measurements from the space-borne Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). For the first time, an evaluation has been performed of six different ozone loss estimation methods based on the same single observational dataset to determine the Arctic ozone loss (mixing ratio loss profiles and the partial-column ozone losses between 380 and 550 K). The methods used are the tracer-tracer correlation, the artificial tracer correlation, the average vortex profile descent, and the passive subtraction with model output from both Lagrangian and Eulerian chemical transport models (CTMs). For the tracer-tracer, the artificial tracer, and the average vortex profile descent approaches, various tracers have been used that are also measured by ACE-FTS. From these seven tracers investigated (CH4, N2O, HF, OCS, CFC-11, CFC-12, and CFC-113), we found that CH4, N2O, HF, and CFC-12 are the most suitable tracers for investigating polar stratospheric ozone depletion with ACE-FTS v3.5. The ozone loss estimates (in terms of the mixing ratio as well as total column ozone) are generally in good agreement between the different methods and among the different tracers. However, using the average vortex profile descent technique typically leads to smaller maximum losses (by approximately 15–30 DU) compared to all other methods. The passive subtraction method using output from CTMs generally results in slightly larger losses compared to the techniques that use ACE-FTS measurements only. The ozone loss computed, using both measurements and models, shows the greatest loss during the 2010–2011 Arctic winter. For that year, our results show that maximum ozone loss (2.1–2.7 ppmv) occurred at 460 K. The estimated partial-column ozone loss inside the polar vortex (between 380 and 550 K) using the different methods is 66–103, 61–95, 59–96, 41–89, and 85–122 DU for March 2005, 2007, 2008, 2010, and 2011, respectively. Ozone loss is difficult to diagnose for the Arctic winters during 2005–2006, 2008–2009, 2011–2012, and 2012–2013, because strong polar vortex disturbance or major sudden stratospheric warming events significantly perturbed the polar vortex, thereby limiting the number of measurements available for the analysis of ozone loss.

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