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In this study the mass transport through free turbulent liquid surfaces, or gas/liquid interfaces, is considered. The main direction of mass transfer is perpendicular to the interface, so that a one-dimensional point of view is followed. The equations for the interfacial gas/liquid transport are presented using the random square waves method (RSW), a statistical tool that models the fluctuations of physical variables as ideal signals. The method defines three statistical functions (partition, reduction, and superposition), related to fluctuations of concentration and velocity, which were introduced into the mass advection-diffusion equation generating a set of differential equations adequate for boundary layer problems. Solution profiles of the partition and reduction functions, and of turbulent fluxes across the boundary layer were obtained for transient situations. The solutions use Taylor series centered at the immersed border of the concentration boundary layer. For practical applications, the series were truncated and the coefficients were calculated in order to satisfy adequate physical conditions. The proposed procedure substitutes coefficients of the higher order parcels of the truncated series, enabling them to satisfy boundary conditions in the two borders of the domain of interest, which is the region of variation of the mass concentration. The theoretical profiles for concentration and turbulent fluxes close to the interface agree with measurements and predictions found in the literature. [ABSTRACT FROM AUTHOR]

Carbon (C) allocation and nonstructural carbon (NSC) dynamics play essential roles in plant growth and survival under stress and disturbance. However, quantitative understanding of these processes remains limited. Here we propose a framework where we connect commonly measured carbon cycle components (eddy covariance fluxes of canopy CO2 exchange, soil CO2 efflux, and allometry‐based biomass and net primary production) by a simple mass balance model to derive ecosystem‐level NSC dynamics (NSCi), C translocation (dCi), and the biomass production efficiency (BPEi) in above‐ and belowground plant (i = agp and bgp) compartments. We applied this framework to two long‐term monitored loblolly pine (Pinus taeda) plantations of different ages in North Carolina and characterized the variations of NSC and allocation in years under normal and drought conditions. The results indicated that the young stand did not have net NSC flux at the annual scale, whereas the mature stand stored a near‐constant proportion of new assimilates as NSC every year under normal conditions, which was comparable in magnitude to new structural growth. Roots consumed NSC in drought and stored a significant amount of NSC post drought. The above‐ and belowground dCi and BPEi varied more from year to year in the young stand and approached a relatively stable pattern in the mature stand. The belowground BPEbgp differed the most between the young and mature stands and was most responsive to drought. With the internal C dynamics quantified, this framework may also improve biomass production estimation, which reveals the variations resulting from droughts. Overall, these quantified ecosystem‐scale dynamics were consistent with existing evidence from tree‐based manipulative experiments and measurements and demonstrated that combining the continuous fluxes as proposed here can provide additional information about plant internal C dynamics. Given that it is based on broadly available flux data, the proposed framework is promising to improve the allocation algorithms in ecosystem C cycle models and offers new insights into observed variability in soil–plant–climate interactions. [ABSTRACT FROM AUTHOR]

The effects of walking speed, crowd density and human-to-source distance on pollutant dispersion in two scaled room models are investigated using simultaneous planar laser-induced fluorescence and particle-image velocimetry techniques. For a small 3 m high room, where the length-scales of the people and room are comparable, the walking motions significantly influenced the macro room mean flow patterns. This has a strong effect on the scalar dispersion properties as the magnitudes of the advective scalar fluxes are often comparable or larger than the turbulent scalar fluxes. As such, the scalar dispersion properties are case specific. For a large 9 m high room, the walking motion influenced only the local mean flow field. The increase in walking speed and crowd density improves the efficiency in which the scalar is transported and mixed with fresh ambient fluid out of the measurement plane (i.e. along the direction of the motion), leading to scalar-free zones observed on the opposite side of the room from the ventilation outlet. The area of the scalar-free zone increases with an increase in the walking speed and crowd density. The advective scalar fluxes are more sensitive to the human motion than the turbulent components, and as the mixing efficiency improves, the advective fluxes show a greater weakening with increased distance from source. The concentration PDFs in the near-source region can be described by the exponential function where the expected value at the 99% percentile can be derived as C 99 / c r m s ′ =4.61, which agreed well with the experimental measurements of 4.1 to 5.9. • Advective and turbulent scalar flux maps reveal underlying transport mechanism • Crowd effects can induce non-uniform and anisotropic scalar mixing • Scalar-free zone observed on the opposite side of the room from ventilation outlet • Dispersion patterns in small rooms are case specific due to non-linear interactions [ABSTRACT FROM AUTHOR]

Benthic fluxes refer to the exchange rates of nutrients and other compounds between the water column and the sediment bed in aquatic ecosystems. Their quantification contributes to our understanding of aquatic ecosystem functioning. Near-bed hydrodynamics plays an important role at the sediment-water interface, especially in shallow lakes, but it is poorly considered by traditional measuring techniques of flux quantification, such as sediment incubations. Thus, alternative sampling techniques are needed to characterize key benthic fluxes under in-situ hydrodynamic conditions. This study aimed to evaluate the performance of two promising methods: relaxed eddy accumulation (REA) and mass transfer coefficient (MTC). We applied them in a hyper-eutrophic shallow lake to measure the fluxes of ammonium, phosphate, iron, and manganese ions. For the first time, REA revealed hourly nutrient flux variations, indicating a strong lake biogeochemical dynamics at short time-scales. Daily average fluxes are of similar orders of magnitude for REA and MTC for ammonium (24 and 42 mmol m2 d−1), manganese (1.0 and 0.8), and iron (0.8 and 0.7) ions. They are one order of magnitude higher than fluxes estimated from sediment incubations, due to the difficulty in reproducing in-situ oxygen and hydrodynamic conditions in the laboratory. Although the accuracy of both techniques needs to be improved, the results revealed their potential: REA follows the short-term biogeochemical dynamics of sediments, while MTC could be widely used for lake monitoring because of its simpler implementation. [Display omitted] • Quantifying benthic fluxes is crucial for understanding aquatic ecosystem functioning. • Turbulence above the sediment-water interface makes it challenging to measure them. • We assessed the performance of two hydrodynamic-dependent methods in a shallow lake. • Fluxes agreed for ammonium, manganese and iron ion fluxes. • One method (REA) revealed short-term dynamics while the other (MTC) proved simple. [ABSTRACT FROM AUTHOR]

Antarctica contains 90% of the Earth's ice; if it melts, it can significantly contribute to the rise in global sea levels. Over Antarctica, short-term atmospheric warming events have led to significant surface melt in summer. Understanding the conditions of such warming events and subsequent surface melt is highly prioritized in Polar Research. The austral summer of 2016-17 witnessed the largest melt duration of the 21st century over Ingrid Christensen Coast (ICC), East Antarctica. Being situated on the grounded ice near four research stations, understanding the melt over the region has both scientific and operational importance. Here, we investigate the drivers of four major melt events identified over ICC for the austral summer of 2016-17 using the reanalysis dataset, ERA5. The first melt event, coinciding with the season's highest air temperature, was triggered by high turbulent heat flux from strong katabatic winds, while the rest of the events were triggered by low-level, liquid cloud-induced longwave radiation. During the melt events, anomalous high pressure ridges were present over the continent causing low pressure systems to remain stationary for an extended period and direct warm, moist air towards the ICC, facilitating melting. The present study observed melting occurring above the grounding zone, and if such melting extends to a larger scale beyond ice shelves, it could raise significant concerns regarding the hydrodynamics and stability of ice sheets in the future. [ABSTRACT FROM AUTHOR]

Copyright of Tecnología y Ciencias del Agua is the property of Instituto Mexicano de Tecnologia del Agua (IMTA) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The scalar dispersion from point sources in indoor spaces is experimentally investigated using simultaneous particle–image velocimetry and planar laser-induced fluorescence techniques in a 20:1 and a 60:1 full-to-model scale room model. The ventilation inlets dominate turbulence production, with magnitudes of the velocities and Reynolds stresses observed to increase with air changes per hour (ACH). Mean concentration maps show a dependence on the ACH and source location which is attributed to the flow field at the near-source region. The peak-to-mean concentration shows a weak dependence on the mean concentration and concentration variance maps, indicating risk for toxic chemicals may be underpredicted if based only on these information. The concentration PDFs are generally well-described by exponential distributions with C 99 / c r m s ′ values never exceeding 5.0. The magnitudes of the advective and turbulent scalar fluxes are strongly dependent on the ACH and source location, neither of which are able to dominate the other by more than an order of magnitude. The eddy diffusivity tensor was measured and a conditional-averaging based method is proposed to approximate it to an isotropic eddy diffusion coefficient, K. For real applications where K is used to estimate magnitudes of the turbulent scalar flux using the gradient transport model, the assumption of isotropic turbulence can introduce an uncertainty of around 17.8%. • Full 2D maps of the scalar fluxes and non-diagonal turbulent diffusivity tensor. • Scalar transport mechanism is dependent on the ACH and source locations. • Anisotropic turbulence contributes to turbulent diffusion coefficient uncertainties. • Implications of inconsistent 'turbulent diffusion coefficient' terminology. [ABSTRACT FROM AUTHOR]

Highlights • An empirical GPP model based on the remotely-sensed plant phenology index (PPI) outperformed three commonly used GPP models. • The PPI-based GPP model was able to explain 77% of the variability in in situ GPP at four arid and semi-arid sites in Africa. • PPI is a new and promising tool for the estimation of GPP in the semi-arid ecosystems of Africa. Abstract The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO 2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO 2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness (T-G) model, the greenness and radiation (GöR) model and a light use efficiency model (MOD17). The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3–65%). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation (R2), root-mean-square error (RMSE), and Bayesian information criterion (BIC). The GöR model produced R2 = 0.73, RMSE = 1.45 g C m−2 d−1, and BIC = 678; the T-G model produced R2 = 0.68, RMSE = 1.57 g C m−2 d−1, and BIC = 707; the MOD17 model produced R2 = 0.49, RMSE = 1.98 g C m−2 d−1, and BIC = 800. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models (R2 = 0.77, RMSE = 1.32 g C m−2 d−1, and BIC = 631). These results show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa. [ABSTRACT FROM AUTHOR]

The effects of a stably-stratified boundary layer on flow and dispersion in a bi-dimensional street canyon with unity aspect ratio have been investigated experimentally in a wind tunnel in combination with differential wall heating. Laser-Doppler anemometry together with a fast flame ionisation detector and cold-wire anemometry were employed to sample velocities, concentration, temperatures and fluxes. A single-vortex pattern was observed in the isothermal case, preserved also when leeward wall was heated, but with a considerable increment of the vortex speed. Heating the windward wall, instead, was found to generate a counter-rotating vortex, resulting in the reduction of velocity within the canopy. The stable stratification also contributes reducing the speed, but only in the lower half of the canyon. The largest values of turbulent kinetic energy were observed above the canopy, while inside they were concentrated close to the windward wall, even when the leeward one was heated. An incoming stable stratification produced a significant and generalised turbulence reduction in all the cases. Windward heating was found to produce larger temperature increments within the canopy, while in the leeward case heat was immediately vacated above the canopy. A stable approaching flow reduced both the temperature and the heat fluxes. A passive tracer was released from a point source located at ground level at the centre of the street canyon. The resulting plume cross-section pattern was mostly affected by the windward wall heating, which produced an increment of the pollutant concentration on the windward side by breaking the main vortex circulation. The application of an incoming stable stratification created a generalised increment of pollutant within the canopy, with concentrations twice as large. Turbulent pollutant fluxes were found significant only at roof level and close to the source. On the other hand, in the windward wall-heated case the reduction of the mean flux renders the turbulent component relevant in other locations as well. The present work highlights the importance of boundary layer stratification and local heating, both capable of creating significant modifications in the flow and pollutant fields at microscale range. • Thermal effects can strongly affect flow and dispersion around buildings. • Both incoming stratified boundary layer and local heating are considered. • A simplified 2D street canyon configuration was investigated in a wind tunnel. • Strong effects of both upwind and local stratification are found. • Extensive dataset produced can be used for model validation and development. [ABSTRACT FROM AUTHOR]

Urban atmospheric flows are vital to the global ecology. This study characterizes urban canopy layer (UCL) dynamics and parameterizes the flows in the atmospheric surface layer (ASL) over heterogeneous urban surfaces. Large-eddy simulations (LESs) are used to transiently calculate the winds over a real, dense city. A linear function of eddy diffusivity of momentum K M is applied to the lower UCL. Analogous to its mixing-layer counterpart, the strong UCL top shear manifests an inflected mean wind speed profile which aligns well with the exponential law. The solutions to the mixing length l m and the turbulent momentum flux are analytically derived by consolidating the mixing-layer type shear and the form drag from the explicitly resolved roughness elements. The behavior of l m in the lower UCL, especially its peaked level, is captured well. Based on the balance between shear and form drag, an aerodynamic effective roof level H ae is designated where the ground effect is alleviated under shear dominance. Results reveal that a rougher urban surface generates eddies with a larger shear length scale, thus enhancing momentum transport. In-canopy turbulence mixing, which slows down wind decay, is also enhanced, resulting in stronger street-level breezes. The newly developed ASL flow model will be beneficial to urban planning by offering reliable predictions, effectuating the management of urban sustainability. [Display omitted] • Model the eddy dynamics and turbulent transport in the atmospheric flows over a city. • Use the mixing-layer analogy to diagnose the winds in urban canopy layers (UCLs). • Parameterize the mixing length and turbulent momentum flux of UCL flows. • Incorporate urban-surface heterogeneity into UCL flow indicators. • Formulate urban morphological factors for UCL winds and pedestrian-level ventilation. [ABSTRACT FROM AUTHOR]

Understanding the detailed mechanism of pollutant dispersion in urban areas is a critical aspect of air quality control in residential areas. In this study, wind tunnel measurements and high-resolution computational fluid dynamic (CFD) based on large eddy simulation (LES) were used for the detailed analysis of the pollutant dispersion around a high-rise building for an isolated case and also a case when the central high-rise building was surrounded by several low-rise buildings. The pollutant was released on the leeward façade of the high-rise building at the pedestrian height. It was shown that the presence of the surrounding buildings significantly alters the pollutant transfer mechanism around the high-rise building. In the surrounded case, the pollutant in the wake region shifted vertically toward the roof of the high-rise building. As a result, at a location of 2/3 of the high-rise building height, the mean concentration is five times larger than the isolated case, which means the residents on higher floors experience more pollution concentration in the case of the surrounded case even though they are located much higher than the canyon rooftop and the pollutant source. In both cases, the contribution of the turbulent diffusive flux in the streamwise direction is comparable with the mean convective flux while they have opposite directions. Detailed analyses of the pollutant mass transfer rate budget around different control volumes around the high-rise buildings highlighted the effect of the surrounding buildings. It is concluded that there is a risk of underestimating pollutant concentrations around a high-rise building, especially near the upper floors if the surrounding buildings are not properly considered. • Impact of surrounding buildings on pollution dispersion was studied numerically. • Pollutant transfer mechanism altered in the presence of surrounding buildings. • Surrounding buildings moved the pollutant vertically toward the higher floors. • Contribution of pollutant streamwise turbulent flux was notable in the wake region. • Turbulent and mean fluxes had opposite directions on some CVs around the builidng. [ABSTRACT FROM AUTHOR]

Due to the practical space limitation, the control valve in industrial utilities is usually immediately followed by a short flow passage, which would introduce considerable complexity into highly unsteady flow behaviors, along with the flow noise and structure vibration. In the present study, the unsteady behaviors of the steam flow inside a control valve with a T-junction discharge, when the valve operates under the choked condition, are numerically simulated. Toward this end, the detached eddy simulation (DES) is used to capture the spatiotemporally varying flow field in the serpentine flow passage. The results show periodic fluctuations of the aerodynamic forces on the valve spindle and periodic fluctuations of the pressure and flow rate at the two discharge outlets. Subsequently, proper orthogonal decomposition (POD) analysis is conducted using the velocity field and pressure field, identifying, respectively, the dominant coherent structures and energetic pressure fluctuation modes. Finally, the extended-POD method is used to delineate the coupling between the pressure fluctuations with the dominant flow structures superimposed in the highly unsteady flow field. The fourth velocity mode at St = 0.1, which corresponds to the alternating oscillations of the annular wall-attached jet, is determined to cause the periodic flow imbalance at the two discharge outlets, whereas signatures of the first three modes are found to be dissipated in the spherical chamber. Such findings could serve as facts for vibration prediction and optimization design. Particularly, the POD and extended-POD techniques were demonstrated to be effective methodologies for analyzing the highly turbulent flows in engineering fluid mechanics. [ABSTRACT FROM AUTHOR]

Pollutant mass fluxes are rarely measured in the laboratory, especially their turbulent component. They play a major role in the dispersion of gases in urban areas and modern mathematical models often attempt some sort of parametrisation. An experimental technique to measure mean and turbulent fluxes in an idealised urban array was developed and applied to improve our understanding of how the fluxes are distributed in a dense street canyon network. As expected, horizontal advective scalar fluxes were found to be dominant compared with the turbulent components. This is an important result because it reduces the complexity in developing parametrisations for street network models. On the other hand, vertical mean and turbulent fluxes appear to be approximately of the same order of magnitude. Building height variability does not appear to affect the exchange process significantly, while the presence of isolated taller buildings upwind of the area of interest does. One of the most interesting results, again, is the fact that even very simple and regular geometries lead to complex advective patterns at intersections: parametrisations derived from measurements in simpler geometries are unlikely to capture the full complexity of a real urban area. [ABSTRACT FROM AUTHOR]

Accurate measurement of ammonia (NH 3 ) emissions from livestock pens is challenging. Two micrometeorological techniques, the integrated horizontal flux (IHF) and the backward Lagrangian stochastic (bLS) dispersion techniques were used to measure NH 3 emissions from an isolated cattle pen (20 × 20 m) in Victoria, Australia. The bLS technique is simple and insensitive to the presence of animals, but typically gives discontinuous measurements due to the need for target wind directions and wind conditions above accepted thresholds. In contrast, the IHF technique as implemented here gives near-continuous measurements with no restriction on wind directions. However, IHF needs more complex field measurements, and there are ambiguities when applied to an animal pen due to the presence of animals. Over the 29 days of our experiment, we collected 124 coincidental bLS and IHF emission measurements from the pen (30−min each). We found no statistical difference in the bLS and IHF calculations when the IHF turbulent flux correction factor ( TF cor ) was set to 15%. Our results confirm that the IHF and bLS techniques, using independent sensors and having very different equipment layouts, gives nearly equivalent results. This suggests the choice of the two methods in future experiments can focus on their different strengths and weaknesses. [ABSTRACT FROM AUTHOR]

An adaptive method for detached-eddy simulation (DES) is tested by simulations of flow in a family of three-dimensional (3D) diffusers. The adaptive method either adjusts the model constant or defaults to a bound if the grid is too coarse. On the present grids, the adaptive method adjusts the model constant over most of the flow, without resorting to the default. Data for the diffuser family were created by wall-resolved, large-eddy simulation (LES), using the dynamic Smagorinsky model, for the purpose of testing turbulence models. The family is a parameterized set o f geometries that allows one to test whether the pattern of separation is moving correctly from the top to the side wall as the parameter increases. The adaptive DES model is quite accurate in this regard. It is found to predict the mean velocity accurately, but the pressure coefficient is underpredicted. The latter is due to the onset of separation being slightly earlier in the DES than in the LES. [ABSTRACT FROM AUTHOR]

In a tunnel fire, the production of smoke and toxic gases remains the principal prejudicial factors to users. The heat is not considered as a major direct danger to users since temperatures up to man level do not reach tenable situations that after a relatively long time except near the fire source. However, the temperatures under ceiling can exceed the thresholds conditions and can thus cause structural collapse of infrastructure. This paper presents a numerical analysis of smoke hazard in tunnel fires with different aspect ratio by large eddy simulation. Results show that the CO concentration increases as the aspect ratio decreases and decreases with the longitudinal ventilation velocity. CFD predicted maximum smoke temperatures are compared to the calculated values using the model of Li et al. and then compared with those given by the empirical equation proposed by kurioka et al. A reasonable good agreement has been obtained. The backlayering length decreases as the ventilation velocity increases and this decrease fell into good exponential decay. The dimensionless interface height and the region of bad visibility increases with the aspect ratio of the tunnel cross-sectional geometry. [ABSTRACT FROM AUTHOR]

This study focuses on interactions of vortices generated by a family of eddy-promoting upstream rectangular cylinders (of different heights a* and widths b*) with the shear layers of a downstream square cylinder (of height A*) placed near a plane in an in-line tandem arrangement under the incidence of Couette-Poiseuille flow based nonuniform linear!nonlinear velocity profile. The dimensionless operational parameters are cylinders spacing distance S, ratio of heights r2 = a*/A* (≤1), aspect ratio rl = b*/a* (≤1), Reynolds number Re (based on the velocity at height A* for Couette flow), ReU2 (based on the velocity at height 10A* for Couette-Poiseuille flow), and nondimensional pressure gradient P at the inlet. The governing equations are solved numerically through a pressure correction- based iterative algorithm (SIMPLE) with the quadratic upwind interpolation for convective kinematics (QUICK) scheme for convective terms. The major issue of appearing multiple peaks in the spectrum of the fluctuating lift coefficient of the downstream cylinder is addressed and justified exhibiting the flow patterns. While considering the rectangular shape (for the upstream cylinder) and nonlinear velocity (at the inlet), the possibility of generating the unsteadiness in the steady wake flow of the downstream cylinder at a Re (based on height a*) less than the critical Re for the downstream cylinder is documented here. The dependence of flow characteristics of the downstream cylinder on the angle of incident linear velocity at specific S and rl is also demonstrated here. It is observed that the discontinuous jump in the aerodynamic characteristics (due to a sudden change from one distinct flow pattern to the other in the critical spacing distance regime) is directly proportional to the height of the vortex generator. Increasing P under the same characteristic velocity causes the steady flow of cylinder)s) to convert to a periodic flow and reduces the critical spacing distance for the vortex generator [ABSTRACT FROM AUTHOR]

Copyright of Atmosphere -- Ocean (Taylor & Francis Ltd) is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For the first time, emission/deposition fluxes of volatile organic compounds (VOCs) and H 2 S from a historic closed landfill site in Southern Italy were determined by Eddy Covariance (EC) using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). This was done in two field campaigns of one week performed in July and October 2016, where fluxes of CO 2 and CH 4 were also measured. Many compounds not previously identified in the biogas were detected by PTR-TOF-MS, but only in July some of them produced positive fluxes exceeding the flux limit of detection. Methanol was the most emitted compound with an average flux of 44.20 ± 4.28 μg m−2 h−1, followed by toluene with a mean flux of 18.97 ± 2.47 μg m−2 h−1. Toluene fluxes were 10 times higher than those of benzene, fitting rather well with values previously measured in the biogas. VOCs emission fluxes of monoterpenes and highly reactive arenes did not reflect, however, the biogas composition. This, combined with tiny emissions of VOC oxidation products, suggests that landfill emissions underwent some photochemical degradation before being dispersed in the atmospheric boundary layer (ABL). Deposition fluxes of some VOCs emitted from the sea was also observed in July. No relevant VOC fluxes were instead measured in October, suggesting that temperature was the variable controlling most landfill emission. Albeit small, summer landfill emissions from the investigated site can have an impact on the population living nearby, because they contain or still generate compounds that causing nuisance. [Display omitted] • VOCs from landfills by Proton Transfer Reaction Time-of-Flight Mass Spectrometer. • Eddy Covariance turbulent fluxes of VOCs, CO 2 and CH 4 from landfills. • Summer fluxes of VOCs and H 2 S not previously identified in the biogas were measured. • No relevant fluxes of VOCs and H 2 S were measured in autumn. • Methanol was the most emitted compound followed by toluene. [ABSTRACT FROM AUTHOR]

A detached eddy simulation of Reentry-F flight vehicle is conducted to investigate its base flow structure. The result shows that DES predicts more accurate heat transfer rates compared to the flight experiment data than laminar and RANS (Spalart-Allmaras model) simulations. The initial vortex surface of base flow field is of toroidal shape, but the decrease of recirculation region cross section area forces the vortex surface first to shrink, then breakdown and reunite, and finally curl to several x-axis elongated vortex surfaces. These x-axis elongated vortex surfaces are origin for the strips distribution of temperature contour on the z=0 plane. [ABSTRACT FROM AUTHOR]

Copyright of Atmosphere -- Ocean (Taylor & Francis Ltd) is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cities constitute an important source of greenhouse gases, but few results originating from long-term, direct CO 2 emission monitoring efforts have been reported. In this study, CO 2 emissions were quasi-continuously measured in an urban center in Sakai, Osaka, Japan by the eddy covariance method from 2010 to 2021. Long-term CO 2 emissions reached 22.2 ± 2.0 kg CO 2 m−2 yr−1 from 2010 to 2019 (± denotes the standard deviation) in the western sector from the tower representing the densely built-up area. Throughout the decade, the annual CO 2 emissions remained stable. According to an emission inventory, traffic emissions represented the major source of CO 2 emissions within the flux footprint. The interannual variations in the annual CO 2 flux were positively correlated with the mean annual traffic counts at two highway entrances and exits. The CO 2 emissions decreased suddenly, by 32% ± 3.1%, in April and May 2020 during the period in which the first state of emergency associated with COVID-19 was declared. The annual CO 2 emissions also decreased by 25% ± 3.1% in 2020. Direct long-term observations of CO 2 emissions comprise a useful tool to monitor future emission reductions and sudden disruptions in emissions, such as those beginning in 2020 during the COVID-19 pandemic. [Display omitted] • The urban center in Sakai, Japan, was a net source of CO 2 on multiple timescales. • The annual CO 2 emissions remained stable from 2010 to 2019. • Interannual variations in the CO 2 emission were correlated with traffic counts. • The annual CO 2 emissions decreased by 25% in 2020 associated with COVID-19. • Inventory suggests traffic CO 2 emissions contributed to 60% of the total emissions. [ABSTRACT FROM AUTHOR]

Abstract: Water and suspended sediment fluxes are considered during the period 2000–2008 in a region including the full Amazon River from the confluence of the Negro River to Santarém, the end part of the Solimões River, and the lower part of the Madeira River. Three types of data are used: water discharge estimated from field measurements, and suspended sediment obtained from field measurements and derived from MODIS satellite data. A generalized least square method including a propagating term is developed in order to propagate the signal upward and downward the river. The approach is introduced and tested. Several experiments are considered in order, first, to estimate the ability to propagate the signal from stations located before the confluences of Negro and Madeira Rivers to stations located on the Amazon River; second to investigate the possibility to propagate the signal along the Amazon River which dynamics is coupled with floodplains dynamics; and third to produce optimal solutions of water and sediment fluxes. For each experiment, the influence of field and satellite data is compared. The approach is efficient in the upper part of the region of study where the Solimões, the Negro and the Madeira Rivers meet and fails in the lower part of the region where interactions between Amazon River and floodplains play an important role on the fluxes’ dynamics. The optimal experiment includes in situ and satellite data from all the stations available and is used to analyse the recent evolution of suspended sediment flux along the Amazon River and its interaction with the large coupled floodplains. A high accumulation rate is observed during the 2000–2002 period, followed by decreasing rates until 2005 and by increasing values in 2006 and 2007. Our results suggest that floodplains extending along a river reach of 390km-long between Itacoatiara and Óbidos trap about 15% of the suspended sediment flux passing at Óbidos. The simulated deposition rate is of about 0.3Mtkm−1 yr−1 corresponding to an accretion rate of about 27mmyr−1. [Copyright &y& Elsevier]

The basic dynamic and diffusion characteristics in several types stable/neutral PBL turbulent regimes are determined on the basis of applied oriented complex method, which accounts for the influence of free-flow stability effects is demonstrated. In particular the results can be used for parameterisation of dynamic and diffusion processes in PBL under such conditions. [ABSTRACT FROM AUTHOR]

The article offers information on the study regarding the use of sediment trap to understand the downward particulate organic carbon (POC) export in the ice zone of eastern Fram Strait and the effect of Atlantic water on POC fluxes. It mentions that POC fluxes feature diatom fluxes, low fecal pellet fluxes from zooplankton, and coccolithophores which is caused by ice-edge eddy that brings warm Atlantic water. It says that Atlantic water contributes to magnitude and composition of fluxes.

This paper presents a unified slip model for axial, radial, and mixed-flow impellers. The core assumption of the model is that the flow deviation or the slip velocity at the impeller exit is mainly originated from the blade loading near the discharge of an impeller and its subsequent relative eddy in the impeller passage. The blade loading is estimated and then used to derive the slip velocity using Stodola's assumption. The final form of the slip factor model can be successfully related to Carter's rule for axial impellers and Stodola's slip model for radial impellers, making the case for this model applicable to axial, radial, and mixed-flow impellers. Unlike conventional slip factor models for radial impellers, the new slip model suggests that the flow coefficient at the impeller exit is an important variable for the slip factor when there is significant blade turning at the impeller discharge. This explains the interesting off-design trends for slip factor observed from experiments, such as the rise of the slip factor with flow coefficient in the Eckardt A impeller. Extensive validation results for this new model are presented in this paper. Several cases are studied in detail to demonstrate how this new model can capture the slip factor variation at the off-design conditions. Furthermore, a large number of test data from more than 90 different compressors, pumps, and blowers were collected. Most cases are radial impellers, but a few axial impellers are also included. The test data and model predictions of the slip factor are compared at both design and off-design flow conditions. In total, over 1650 different flow conditions are evaluated. The unified model shows a clear advantage over the traditional slip factor correlations, such as the Busemann-Wiesner model, when off-design conditions are considered. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents numerical simulations of the aerodynamic effects of trees on the flow field and dispersion of trafficoriginated pollutants in an urban street canyon of W/H = 1 with a perpendicular approach flow. Large Eddy Simulation (LES) is employed for the investigation and is validated against wind tunnel (WT) experiment. Comparisons is made between an empty street canyon and one containing avenue-like tree planting of pore volume, Pvol =96%. In the presence of trees, both measurements and simulations show considerably larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall in comparison to the tree-free case. [Copyright &y& Elsevier]

The article investigates the relative magnitude and contribution of parameter and driver uncertainty in predictions of forest carbon dynamics to separate driver error from model error. It concludes that models may be impractical to measure, while driver fields are rarely complete due to sensor failure and sparse observational networks. Also discussed is the generation of acceptable parameterizations using an ensemble Kalman filter and eddy covariance measurements of net carbon fluxes.

The article examines the information content of planetary boundary layer (PBL) measurements to demonstrate consistency between the coupled atmosphere-biosphere (CAB) model and to use this model in a set of Bayesian experiment. It reveals that the model will be demonstrated by comparing the model to eddy covariance flux tower measurements and PBL scalar profile measurements. It concludes the similarities of the abilities of the PBL profiles and the covariance data to constrain the parameters.

Abstract: In this paper, we study the impact of density ratio on turbulent liquid jet in crossflow penetration and atomization if all other characteristic parameters, i.e., momentum flux ratio, jet and crossflow Weber and Reynolds numbers, are maintained constant. We perform detailed simulations of the primary atomization region using the refined level set grid method to track the motion of the liquid/gas phase interface. We employ a balanced force, interface projected curvature method to ensure high accuracy of the surface tension forces, use a multi-scale approach to transfer broken-off, small scale nearly spherical drops into a Lagrangian point particle description allowing for full two-way coupling and continued secondary atomization, and employ a dynamic Smagorinsky large eddy simulation approach in the single phase regions of the flow to describe turbulence. We compare simulation results obtained previously using a liquid to gas density ratio of 10 for a momentum flux ratio 6.6, Weber number 330, and Reynolds number 14,000 liquid jet injected into a Reynolds number 740,000 gaseous crossflow to those at a density ratio of 100, a value typical for gas turbine combustors. The results show that the increase in density ratio results in a noticeable increase in jet penetration, change in drop size distribution resulting from primary atomization, change in drop velocities generated by primary atomization in the crossflow and jet direction, but virtually no change in drop velocities in the transverse direction. [ABSTRACT FROM AUTHOR]

Scalar, eddy viscosity models are widely used for predicting engineering turbulent flows. System rotation, or streamline curvature, can enhance or reduce the intensity of turbulence. Methods to incorporate the effects of rotation and streamline curvature consist of introducing parametric variation of model coefficients, such that either the growth rate of turbulent energy is altered; or such that the equilibrium solution bifurcates from healthy to decaying solution branches. For general use, parameters must be developed in coordinate invariant forms. Effects of rotation and of curvature can be unified by introducing the convective derivative of the rate of strain eigenvectors as their measure. [ABSTRACT FROM AUTHOR]

The performance of some commonly used eddy-viscosity turbulence models has been evaluated using direct numerical simulation (DNS) and large-eddy simulation (LES) data. Two configurations have been tested, a two-dimensional boundary layer undergoing pressure-driven separation, and a square duct. The DNS and LES were used to assess the k - ϵ, ζ - f, k - ω, and Spalart-Alimaras models. For the two-dimensional separated boundary layer anisorropic effects are not significant and the eddy-viscosity assumption works well. However the near-wall treatment used in k - ϵ models was found to have a critical effect on the predictive accuracy of the model (and, in particular of separation and reattachment points). None of the wall treatments tested resulted in accurate prediction of the flow field. Better results were obtained with models that do not require special treatment in the inner layer (ζ -f, k - ω, and Spalart-Allmaras models). For the square duct calculation, only a nonlinear constitutive relation was found to be able to capture the secondary flow, giving results in agreement with the data. Linear models had significant error. [ABSTRACT FROM AUTHOR]

Abstract: Fluxes of CO2 (FCO2) and energy (latent heat, LE; sensible heat, H) exchange between ecosystems and atmosphere, as measured by the eddy covariance technique, represent a fundamental data source for global-change research. However, little is known about the uncertainties of flux measurements at an ecosystem level in China. Here, we use data from six eddy covariance tower sites in ChinaFLUX, including two forested sites, three grassland sites, and one agricultural site, to conduct a cross-site analysis of random flux errors (RFEs) of FCO2, LE, and H. By using the daily-differencing approach, paired observations are obtained to characterize the random error in these measurements. Our results show that: (1) The RFEs of FCO2, LE, and H in different ecosystems of ChinaFLUX closely follow a double-exponential (Laplace) distribution, presumably due to a superposition of Gaussian distribution for high flux magnitude. (2) The RFEs of FCO2, LE, and H are not homogeneous and appear to be a linear function of flux magnitude. (3) Except for H, the RFEs of FCO2 and LE exhibit a distinct seasonal pattern. For FCO2, the dependence of RFEs on wind speed varies somewhat according to vegetation type, whereas for LE and H, there is no such dependence. The effect of temperature on RFEs is not statistically significant (P <0.05). Both the distribution and the relationship of RFEs with flux magnitude in ChinaFLUX are essentially in accord with those in AmeriFlux and CarboEurope. [ABSTRACT FROM AUTHOR]

Turbulent flow and heat transfer in a rectangular duct with cross-sectional aspect ratio b/a =2 rotating along its spanwise direction were investigated by large eddy simulation. The unsteady N-S equations were discretized based on the inconsistent fixed scheme (Adams-Bashforth/Crank- Nicholson) with the second-order precision. And the dynamic subgrid-scale model was used to evaluate the Reynolds stresses. The simulations were performed for a Reynolds number of 400, while the Prandtl number (Pr) was assumed to be 0. 71. The rotation number was changed from 0 to 5. The averaged velocity, temperature and turbulent kinetic energy intensity distribution were analyzed in the cross section of the rectangular duct. The results show that the effects of system rotation with different rotating axes have an important influence on the turbulent flow and heat transfer. It is found that the turbulent flow structure is changed obviously near the stable wall and unstable wall at high rotation number. At the same rotation number, the average heat transfer coefficient of the rotation axis paralleling the y axis is greater than that of the rotation axis paralleling the z axis. [ABSTRACT FROM AUTHOR]

The turbulence effect of hot and cold fluids mixing in the tee-junction led to fluctuations of velocity, which is the essential cause of fluid flow inducing thermal fatigue of pipe. In order to reveal the cause, fluids mixing for the case with hot fluid in main duct and cold fluid in branch duct of a tee-junction was numerically simulated by large-eddy simulation. Numerical results of time-averaged and root-mean square velocities were compared with experimental results in a profile. The good agreement of numerical results with experimental ones indicates that large-eddy simulation can exactly predict the time-averaged velocity and velocity fluctuation of mixing process. Numerical results show that the profiles of time-averaged and root-mean square velocities in x and z directions along z direction have the trend of becoming uniform with the increase of x/db and decreasing with the increase of y/db. [ABSTRACT FROM AUTHOR]

To assess a density modify based turbulence model,the unsteady cloud cavitating flow around a Clark-y hydrofoil is investigated by coupled experimental and numerical methods. A high speed camera is used to visualize the flow structures, and laser Doppler velocity (LDV) is employed for velocity measurement. The numerical simulations are conducted on the two dimensional hydrofoil section, the different turbulence models including the density modify based turbulence model are used for computation. It is shown that the new model can predict successively the characteristic of cavitation and the detail process of the cavitation shedding through adjusting the eddy viscosities. The average flow velocity values accord basically with the experimental results. [ABSTRACT FROM AUTHOR]

The article presents the study of time-series estimates using the net ecosystem carbon exchange (NEE) model with the application of eddy covariance techniques and embedded in an ensemble Kalman filter (EnKF). Researchers employ a model testing in estimating the dynamic variables on the changes of leaf phenology in Alaska and uses two modifications of EnKF. It presents that there is a deficiency on the model due to the vapor pressure which affects the canopy conductance.

Time-dependent computational simulations on cavity filling process by cold gas dynamic spray and powder jet deposition process ranging from microscale to macroscale were carried out in order to give an insight for their advanced applications to joining, crack repair and dental treatment. Shock wave appears in front of the substrate due to under-expansion of jet and in-flight particles interact with the shock wave before their impact. The relation between shock wave, cavity configuration, and particle in-flight behavior in supersonic jet has been discussed in detail. Based on numerical and experimental studies, it was found that when the shock wave covers up the cylindrical cavity, the cavity cannot be filled at all by deposited powders. Moreover under the condition of shock wave appearing inside the cylindrical cavity, conical deposition was formed due to the secondary back flow jet along the cavity side wall. By adopting conical cavity, cavity can be filled completely resulting from the suppression of the secondary back flow jet along the cavity side wall. [ABSTRACT FROM AUTHOR]

In this paper the flow field of a rectangular synthetic jet driven by a piezoelectric membrane issuing into a quiescent environment is studied. The similarities exhibited by synthetic and continuous turbulent jets lead to the hypothesis that a rectangular synthetic jet within a limited region downstream of the orifice be modeled using similarity analysis just as a continuous planar jet. Accordingly, the jet is modeled using the classic two dimensional solution to a continuous jet, where the virtual viscosity coefficient of the continuous turbulent jet is replaced with that measured for a synthetic jet. The virtual viscosity of the synthetic jet at a particular axial location is related to the spreading rate and velocity decay rate of the jet. Hot-wire anemometry is used to characterize the flow downstream of the orifice. The flow field of rectangular synthetic jets is thought to consist of four regions as distinguished by the centerline velocity decay. The regions are the developing, the quasi-two-dimensional, the transitional, and the axisymmetric regions. It is in the quasi-two-dimensional region that the planar model applies, and where indeed the jet exhibits self-similar behavior as distinguished by the collapse of the lateral time average velocity profiles when scaled. Furthermore, within this region the spanwise velocity profiles display a saddleback profile that is attributed to the secondary flow generated at the smaller edges of the rectangular orifice. The scaled spreading and decay rates are seen to increase with stroke ratio and be independent of Reynolds number However, the geometry of the actuator is seen to additionally affect the external characteristics of the jet. The eddy viscosities of the synthetic jets under consideration are shown to be larger than equivalent continuous turbulent jets. This enhanced eddy viscosity is attributed to the additional mixing brought about by the introduction of the periodic vortical structures in synthetic jets and their ensuing break down and transition to turbulence. Further, a semi-empirical modeling approach is proposed, the final objective of which is to obtain a functional relationship between the parameters that describe the external flow field of the synthetic jet and the input operational parameters to the system. [ABSTRACT FROM AUTHOR]

Abstract: The call for environmentally compatible and economical vehicles, still satisfying demands for high performance, necessitates immense efforts to develop innovative engine concepts. Whereas direct injection gasoline engines promise considerable fuel savings, they are prone to large variations in the flow and mixing field. These fluctuations may result in combustion failures leading to a total loss of the energy stored in a full cylinder load and to the ejection of un-burnt hydrocarbons into the environment. The present work aims at investigating the impact of the phenomena of cycle-to-cycle variations on air–fuel mixing processes in a realistic IC-engine using LES. The configuration under study represents a generic four-stroke direct spray injection engine with variable charge motion system. To appraise the numerical predictions, available experimental data are first compared to LES achievements. The LES is then assessed by means of two index of quality. Finally, the impact of the cycle-to-cycle velocity fluctuations on the spray propagation and mixing processes is pointed out with emphasis on results close to the ignition point. [Copyright &y& Elsevier]

Abstract: While most academic set ups used to study combustion instabilities are limited to single burners and are submitted mainly to longitudinal acoustic modes, real gas turbines exhibit mostly azimuthal modes due to the annular shape of their chambers. This study presents a massively parallel Large Eddy Simulation (LES) of a full helicopter combustion chamber in which a self-excited azimuthal mode develops naturally. The whole chamber is computed from the diffuser outlet to the high pressure stator nozzle. LES captures this self-excited instability and results (unsteady pressure RMS and phase fields) show that it is characterized by two superimposed rotating modes with different amplitudes. These turning modes modulate the flow rate through the 15 burners and the flames oscillate back and forth in front of each burner, leading to local heat release fluctuations. LES demonstrates that the first effect of the turning modes is to induce longitudinal pulsations of the flow rates through individual burners. The transfer functions of all burners are the same and no mechanism of flame interactions between burners within the chamber is identified. [Copyright &y& Elsevier]

Abstract: A large-eddy simulation (LES) model with a new localized dynamic subgrid closure for the magnetohydrodynamics (MHD) equations is used to investigate plasma-assisted combustion in supersonic flow. A 16-species and 74-reactions kinetics model is used to simulate hydrogen-air combustion and high-temperature air dissociation. The numerical model is validated with experimental data for non-reacting and reacting supersonic flow over a rearward-facing step. The creation of a plasma source near the step corner is shown to have a strong localized effect with the high temperature region resulting in an increase of the radical species concentration in the mixing region. This has the potential for enhancing combustion. In addition, downstream fuel–air mixing is improved, primarily by the creation of a strong baroclinic torque effect in the near field of the plasma source. Furthermore, by adding an uniform external magnetic field, the Lorentz force effect helps to further enhance mixing by lifting the shear layer and increasing fuel penetration by approximately 20%. [Copyright &y& Elsevier]

Abstract: Large-eddy simulation of an atomizing spray issuing from a gas-turbine injector is performed. The filtered Navier–Stokes equations with dynamic subgrid scale model are solved on unstructured grids to compute the swirling turbulent flow through complex passages of the injector. The collocated grid, incompressible flow algorithm on arbitrary shaped unstructured grids developed by Mahesh et al. (J. Comp. Phys. 197 (2004) 215–240) is used in this work. A Lagrangian point-particle formulation with a stochastic model for droplet breakup is used for the liquid phase. Following Kolmogorov’s concept of viewing solid particle-breakup as a discrete random process, the droplet breakup is considered in the framework of uncorrelated breakup events, independent of the initial droplet size. The size and number density of the newly produced droplets is governed by the Fokker–Planck equation for the evolution of the pdf of droplet radii. The parameters of the model are obtained dynamically by relating them to the local Weber number and resolved scale turbulence properties. A hybrid particle-parcel is used to represent the large number of spray droplets. The predictive capability of the LES together with Lagrangian droplet dynamics models to capture the droplet dispersion characteristics, size distributions, and the spray evolution is examined in detail by comparing it with the spray patternation study for the gas-turbine injector. The present approach is computationally efficient and captures the global features of the fragmentary process of liquid atomization in complex configurations. [Copyright &y& Elsevier]

Abstract: Large-eddy simulation of an evaporating isopropyl alcohol spray in a coaxial combustor is performed. The Favre-averaged, variable density, low-Mach number Navier-Stokes equations are solved on unstructured grids with dynamic subgrid scale model to compute the turbulent gas-phase. The original incompressible flow algorithm for LES on unstructured grids by [Mahesh et al., J. Comp. Phys. 197 (2004) 215–240] is extended to include density variations and droplet evaporation. An efficient particle-tracking scheme on unstructured meshes is developed to compute the dispersed phase. Experimentally measured droplet size distribution and size-velocity correlation near the nozzle exit are used as the inlet conditions for the spray. The predictive capability of the LES approach on unstructured grids together with Lagrangian droplet dynamics models to capture the droplet dispersion characteristics, size distributions, and the spray evolution is examined in detail. The mean and turbulent quantities for the gas and particle phases are compared to experimental data to show good agreement. It is shown that for low evaporation rates considered in the present study, a well resolved large-eddy simulation together with simple subgrid models for droplet evaporation and motion provides good agreement of the mean and turbulent quantities for the gas and droplet phases compared to the experimental data. This work represents an important first step to assess the predictive capability of the unstructured grid LES approach applied to spray vaporization. The novelty of the results presented is that they establish a baseline fidelity in the ability to simulate complex flows on unstructured grids at conditions representative of gas-turbine combustors. [Copyright &y& Elsevier]

Abstract: The Large Eddy Simulation (LES) equations for multicomponent (MC) fuel single-phase (SP) flow and two-phase (TP) flow with phase change are derived from the Direct Numerical Simulation (DNS) equations by filtering the DNS equations using a top-hat filter. Additional to the equations solved for single-component (SC) fuels, composition equations enter the formulation. The species composition is represented through a Probability Distribution Function (PDF), and DNS equations for the PDF moments are solved to find the composition. The TP filtered equations contain three categories of subgrid-scale (SGS) terms: (1) SGS–flux terms, (2) filtered source terms (FSTs) and (3) terms representing the ‘LES assumptions’. For SP flows no FSTs exist. The SGS terms in the LES equations must be either shown negligible or modeled. It is shown that for the composition equations, two equivalent forms of the DNS equations lead to two non-equivalent forms of the LES equations. Criteria are proposed to select the form best suited for LES. These criteria are used in conjunction with evaluations based on a DNS database portraying mixing and phase change, and lead to choosing one of the LES forms which satisfies all criteria. It is shown that the LES assumptions lead to additional SGS terms which require modeling. Further considerations are made for reactive flows. [Copyright &y& Elsevier]

The present study investigates the impact of building façade geometrical details on the pollutant transport mechanism in long street canyons. Large-eddy simulations (LES), extensively validated with experiments, are performed for four cases: (i) street canyon without façade balconies, (ii) street canyon with balconies at both windward and leeward façades, (ii) street canyon with balconies only at the windward façade and (iv) street canyon with balconies only at the leeward façade. The results show that the building balconies can strongly affect the wind flow field and pollutant dispersion in long street canyons. The most significant impact is observed for the two street canyon cases with balconies at the windward façade, which strongly obstruct the airflow from penetrating deep into the bottom of the canyon. The presence of balconies only at the windward façade and at both façades can increase the area-weighted mean pollutant concentration in the vertical center plane inside the canyon by 80% and 106%, respectively, and reduce the mean pollutant exchange velocity (U e) by 46% and 54%, respectively. The analysis of the vertical mean convective and turbulent mass fluxes indicates that the presence of balconies mainly decreases the convective contribution to U e , while the impact on the turbulent contribution is smaller. [Display omitted] • Large-eddy simulations are performed for street canyons with balconies. • Wind flow field and pollutant dispersion inside street canyons are investigated. • Windward balconies strongly obstruct the airflow from entering the canyon. • Presence of balconies increases mean concentration within the canyon by up to 106%. • Presence of balconies reduces the pollutant exchange velocity by up to 54%. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dioxide was released from a shallow horizontal well for ten days at 0.1 t d−1 (Release 1) and for seven days at 0.3 t d−1 (Release 2) during Summer 2007. Net CO2 fluxes () were continuously monitored by eddy covariance during the summers of 2006 and 2007. To improve leakage detection ability, we removed ecosystem fluxes correlated with changes in soil temperature and light intensity from . The Release 2 leakage signal was enhanced in a time series of upper 95th percentile residual , while the Release 1 signal fell within the variability of unmodeled processes. [Copyright &y& Elsevier]

Abstract: The effects of global climate change due to increased greenhouse gas emissions are a growing concern. It is important that technology-based solutions be evaluated in the event they need to be implemented. One method of mitigating anthropogenic CO2 emissions is through geologic storage or sequestration. Most efforts involving Carbon Capture and Storage (CCS) focus on CO2 injection in deep geologic formations. Two issues that arise with CCS technology are public acceptance and monitoring of the horizontal and vertical movements of the CO2 plume. With most CCS sites the risk for leak will be extremely low; however, it will be critical to assure the public of their safety. One way to mitigate public concern is through an integrated surface monitoring campaign. Natural surface background CO2 fluxes must be understood to characterize potential leak sites. LI-COR Biosciences has developed the technology to aid researchers in monitoring potential surface leak sites in areas where CCS is implemented. The LI-8100 Automated Soil CO2 Flux System measures diffusion of CO2 from the soil into the atmosphere, and the LI-7500 Open Path CO2/H2O Analyzer, when integrated with a sonic anemometer, can measure the CO2 flux over a large area. In this paper we discuss these two monitoring methods in detail and present data that illustrates the need for natural surface flux measurements in areas where CCS will be implemented. We will also provide examples of how this technology is currently being used for monitoring CO2 injections at geologic storage sites. [Copyright &y& Elsevier]

Abstract: A field facility has been developed to allow controlled studies of near surface CO2 transport and detection technologies. The key component of the facility is a shallow, slotted horizontal well divided into six zones. The scale and fluxes were designed to address large scale CO2 storage projects and desired retention rates for those projects. A wide variety of detection techniques were deployed by collaborators from 6 national labs, 2 universities, EPRI, and the USGS. Additionally, modeling of CO2 transport and concentrations in the saturated soil and in the vadose zone was conducted. An overview of these results will be presented. [Copyright &y& Elsevier]

Abstract: The paper describes an experimental set-up designed to measure the volatilization of different pesticides after application under full-scale field conditions. The pesticides were sprayed around the circumference of a circle and measurements of meteorology and air concentrations of pesticides were taken in the centre of the circle. The paper describes how the dimensions like the radius of the circle and height of the mast in the experimental set-up are found from theoretical considerations. A method to increase the confidence of the flux calculations is described. It utilizes that several substances were applied simultaneously and that a certain parameter in the fitted concentration profiles depends on turbulence only and thus have the same value for all substances. The design was used during two campaigns, conducted on the same location, one during fall on bare soil and one in spring on a barley crop. [Copyright &y& Elsevier]