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Determining the mixing height using a tracer can improve the information obtained using traditional techniques. Here we provide an improved box model based on radon progeny measurements, which considers the vertical entrainment of residual layers and the variability in the soil radon exhalation rate. The potential issues in using progeny instead of radon have been solved from both a theoretical and experimental perspective; furthermore, the instrumental efficiency and the counting scheme have been included in the model. The applicability range of the box model has been defined by comparing radon-derived estimates with sodar and lidar data. Three intervals have been analyzed (“near-stable”, “transition” and “turbulent”), and different processes have been characterized. We describe a preliminary application case performed in Rome, Italy, while case studies will be required to determine the range limits that can be applied in any circumstances.

This paper examines the mass balance in calculations with the Regional Atmospheric Modelling System (RAMS). An error is pointed out that concerns the calculation of the surface fluxes on slopes. This error affects all the prognostic variables in RAMS when sloping terrain is involved. Here we explain how the error can be corrected. To study the impact of the error, we compared simulations with the uncorrected and corrected model. The model contains CO2 transport, and online mass balance calculations were performed for this tracer. Without correction, effective surface CO2-fluxes on mountain slopes were found to be enhanced under certain common conditions to several times the parameterized fluxes. Neglecting this error may cause substantial deviations in both forward and inverse model calculations. After the correction a very good closure of the mass balance is obtained. The correction also modifies the meteorological parameters, although the consequences were limited compared to the CO2-fluxes.

Astigmatism particle imaging is an optical method to determine the instantaneous volumetric position of spherical particles in a volume of transparent medium using only a single camera view. The method is mainly applied in microfluidics to measure the velocity and trajectories of tracer particles that follow the fluid motion. However, recently it could be shown that this measurement principle without bias errors due to the depth of correlation and spatial averaging is well suited to reconstruct the arbitrary-shaped interface of mixing layers in a micromixer with extended high precision.

Carbon Carbon (chemical symbol C) is an element with six protons in a nucleus circled by six electrons. In addition, the nucleus may contain six, seven, or eight neutrons, which leads to three forms of carbon having 12, 13, and 14 mass units (C,C, C) with a natural relative abundance of 98.9 %, 1.1 %, and ca. 10 10 %, respectively. These three natural forms of carbon, called isotopes, have the same chemical properties but slightly different, mass-dependent, physical properties. The isotope carbon-14 (C) is also called radiocarbon, because it is radioactive, showing beta decay. Carbon is a key building block for life on earth, and its isotopes can be used to study physiological and environmental processes.

Experiments comparing the use of an organic dye and sodium chloride as tracers were evaluated for their effectiveness in describing the hydrological conditions in a pilot-scale constructed channel wetland in semiarid South Texas, USA. This paper summarizes the significance, complexity, and challenges concerning the accuracy of the residence time distribution (RTD) determinations using organic and inorganic tracers in a pilot scale wetland evaluations. It was hypothesized that while an organic tracer had a much lower detection limit, its mass recovery due to sorption to organic surfaces might inhibit its performance and reliability. The pilot-scale RTD experiments were conducted using the organic Rhodamine WT (RWT) dye and sodium chloride (NaCl) as a tracers. Breakthrough curves were interpreted and differences in mass recovery suggested a slightly improved resolution of the wetland dispersive behavior when using RWT than when using NaCl as a tracer in these channel wetland applications. Mass recovery using RWT as a tracer was 67 % for the vegetated channel. Using NaCl, mass recovery was only 43 % in the vegetated channel. The calculated dispersion numbers were slightly higher using RWT (0.20 in the vegetated channel) than when using NaCl as a tracer (0.10 in the vegetated channel). Results from this research suggest some advantages of RWT as a tracer over NaCl due to the high mass recovery; however, both tracers gave similar quantitative results for wetland dispersion estimates.

Traditional monitoring networks measure only total elemental carbon (EC) and organic carbon (OC) routinely. Diagnosing model biases with such limited information is difficult. Measurements of organic tracer compounds have recently become available and allow for more detailed diagnostic evaluation of CMAQ modeling results, which allow for more explicit representation of secondary organic aerosols. An enhanced version of the model makes it possible to track contributions from various sources of primary organic aerosols and elemental carbon, providing more in-depth evaluation of model biases. An ambient PM2.5 measurement campaign conducted in four Midwestern U.S. cities in March 2004 February 2005 allows for direct comparison of modeled and measured organic carbon concentrations by primary and secondary source category.

For the purpose of characterizing geologically stored $$\text{ CO}_{2}$$ including its phase partitioning and migration in deep saline formations, different types of tracers are being developed. Such tracers can be injected with $$\text{ CO}_{2}$$ or water, and their partitioning and/or reactive transfer from one phase to another can give information on the interactions between the two fluid phases and the development of their interfacial area. Kinetic rock–water interactions and geochemical reactions during two-phase flow of $$\text{ CO}_{2}$$ and brine have been incorporated in numerical simulators (e.g., Xu et al., TOUGHREACT User’s Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media. LBNL Report 55460, V.1.2., Berkeley, CA, 2004). However, chemical equilibrium between the fluid phases is typically assumed, and multi-component, multiphase, non-isothermal codes for $$\text{ CO}_{2}$$–brine systems that incorporate kinetic mass transfer of tracers between the two fluid phases are not readily available. New models or further developments of existing models are therefore needed to provide the capability for interpreting the signals of novel tracers, including tracers with kinetic/time-dependent interface transfer. This paper presents such new numerical model of tracer transport in a non-isothermal two-phase flow system. The model consists of five different governing equations describing liquid phase (aqueous) flow, gas ($$\text{ CO}_{2})$$ flow, heat transport and the movement of the tracers within the two phases, as well as allowing kinetic transport of the tracers between the two phases. A finite element method is adopted for the spatial discretization and a finite difference approach is used for temporal discretization. Some special technologies and solution strategies are adopted for increasing the convergence, ensuring the numerical stability and eliminating non-physical oscillations. The new numerical model is validated against the code TOUGH2/ECO2N as well as some analytical/semi-analytical solutions. Good agreement between the simulated and analytical results indicates that the model has capability to simulate two-phase flow and tracer transport in a non-isothermal two-phase flow system with high confidence. Finally, the capability to model transport and kinetic mass transfer of tracers between the two fluid phases is demonstrated through examples. peerReviewed

Among the environmental radioisotopes, tritium is the most attractive to those researchers who are studying the principles of water circulation in nature . It is a constituent of water molecules and, therefore, is a perfect water tracer . The interest in application of tritium for hydrological and meteorological purposes was increased greatly during the period of thermonuclear tests in 1953–1962, and also subsequently when a large amount of this artificially produced isotope had been injected into the atmosphere. The bomb-tritium, injected into the atmosphere by installments after each nuclear test , is a kind of fixed time mark of water involved in water cycling .

A common approach to characterizing aquifer mass transfer properties is the use of tracer tests. Our focus is mostly on tracer tests that employ a forced flow field induced by injection and/or withdrawal wells. Such tests offer advantages for estimating transport properties in porous and fractured media over natural gradient tracer tests (Hydraulic and tracer testing…, 1996). We also will focus on the analysis of models describing the vertical movement of natural saltwater–freshwater interface in thick groundwater systems. The interpretation of the latter process also results in useful information about solute transport properties of systems featuring natural hydrogeochemical stratification. Those models are next modified to account for density difference between the fluids in contact (see Secs. 12.3 and 14.2).

Tracers are defined as chemical substances (inorganic or organic molecules, including isotopes), present naturally or introduced in the environment. A variety of tracers are used in geohydrological investigations for estimating the rate and direction of groundwater movement, groundwater recharge and its residence time. Tracers are also used for the study of origin of groundwaters including saline and geothermal waters, contaminant transport including site characterisation of repositories for nuclear waste, interconnection between surface water and groundwater, stream discharge measurement and sediment transport. There are reports of the use of tracers viz. chloride, fluorescein and bacteria in karst aquifers in Europe even in the late 1800s and early 1900s.

Atmospheric water vapor is a major component of the global hydrological cycle and the isotope ratio of that vapor is a key tracer for both hydrological and biological processes. Yet little is known of the isotopic composition of vapor over any spatial scale and through time because of challenges associated with collecting water vapor samples. Here we discuss alternate methods for measuring water vapor isotopes. The first approach capitalizes on the unique physiology and broad distribution of the epiphytic plant Tillandsia usneoides (Spanish Moss) to reconstruct a growing-season-integrated isotope ratio of water vapor. The second approach utilizes infrared spectroscopy to measure the isotopic composition without sample collection. In situ laser-absorption instruments and emission spectrometers aboard satellites employ similar optical measurement approaches, and while the former lends itself to developing very detailed time series the latter offers resolution of global-scale spatial distributions. These new approaches, while highly disparate, represent novel methods that complement existing collection techniques and enable improved knowledge of both the spatial mean and variation of isotopes in atmospheric water vapor.

Naturally occurring 210 Pb and 210 Po are important tracers used in marine environment studies. In this study, 210 Po and 210 Pb measurements in marine samples (sediment, sea water and biota) were performed using alpha spectrometry. Chemical recoveries are obtained using 209 Po tracer. Two different approaches for 210 Pb determinations are also compared. First, to keep the original samples for about 1 year to eliminate the excess 210 Po and to reach 210 Po- 210 Pb equilibrium before radiochemical separation of 210 Po. The second is to extract the excess 210 Po in the samples, then wait for attaining 210 Pb- 210 Po equilibrium in the solution to obtain 210 Pb activities. In samples, time corrections for excess 210 Po originated from radioactive decay of grand parent are discussed.

The effects of slurry application method and weather conditions after application on ammonia volatilisation are well documented, however, the effect on slurry N recovery in herbage is less evident due to large variability of results. The objective of this field experiment was to determine the recovery of cattle slurry NH4-N in herbage and soil in the year of application as affected by application method (trailing shoe versus broadcast) and season of application (spring versus summer), using 15N as a tracer. In 2007 and 2008, 15N enriched slurry was applied on grassland plots. N recovery in herbage and soil during the year of application was determined. Both spring and trailing shoe application resulted in significantly higher herbage DM yields, N uptake and an increased recovery of 15NH4-N in herbage. Additionally, the recovery of slurry 15NH4-N in the soil at the end of the growing season was increased. Spring and trailing shoe application reduced the losses of slurry 15NH4-N by on average 14 and 18 percentage points, respectively, which corresponded closely to ammonia volatilisation as predicted by the ALFAM model. It was concluded that slurry N recovery in temperate pasture systems can be increased by adjusting the slurry application method or timing. peerReviewed

The principles and survey procedure of the identification of past radiation events on the basis of antedated layers of pond bottom sediments are described. Results of experimental investigations (2005–2006) of sediment samples taken in the Timiryazev Garden pond in Moscow and in the pond of a village Podkhozheye in Moscow district are presented. Dating of bottom layers have been carried out using 210Pb. This radionuclide is used as a tracer to estimate the sedimentation rate in ponds (0.3–0.4 cm/year.). It is shown that the content of 137Cs, the main anthropogenic radionuclide in all fallout of the second part of the 20th century, is relatively higher at the depth 7–8 cm below the bottom surface. This can be explained by the Chernobyl fallout. A second maximum of 11–13 and 17–22 cm (for each of the ponds) can be explained by a global origin. The origin of both of these maxima is confirmed by radionuclide ratios, which are typical for global and Chernobyl depositions at the Moscow region.

To understand ecosystem functioning in coastal zones it is essential to identify the main pathways and magnitude of nutrient and organic matter fluxes. The different methods that have been applied to quantify material fluxes in tropical coastal ecosystems can be categorized into two fundamentally distinct approaches: direct flux measurements (Section 12.2) and chemical tracer techniques (Section 12.3). For direct flux measurements, the bidirectional flow of water is determined and multiplied with concentrations to obtain fluxes of inorganic nutrients or organic constituents. Water discharge can be measured directly with help of current meters and gauges, or indirectly through use of water tracers. The source of nutrients and organic matter can then be identified with help of specific chemical tracers, mainly isotopes or molecular properties. A combination of tracer techniques and direct flux measurements is most powerful to obtain quantitative information on the fluxes of organic matter and nutrients from the various sources in coastal systems but has very rarely been applied. Regarding source assessments of suspended and sedimentary organic matter, a large number of molecular biomarkers are readily available (Section 12.4). For dissolved organic matter, emerging molecular fingerprinting techniques including ultra-high resolution mass spectrometry may lead to major advances in the future.