Atmospheric Tracer Experiments Research Articles

Observation of turbulent dispersion of artificially released SO<sub>2</sub> puffs with UV cameras

Abstract. In atmospheric tracer experiments, a substance is released into the turbulent atmospheric flow to study the dispersion parameters of the atmosphere. That can be done by observing the substance's concentration distribution downwind of the source. Past experiments have suffered from the fact that observations were only made at a few discrete locations and/or at low time resolution. The Comtessa project (Camera Observation and Modelling of 4-D Tracer Dispersion in the Atmosphere) is the first attempt at using ultraviolet (UV) camera observations to sample the three-dimensional (3-D) concentration distribution in the atmospheric boundary layer at high spatial and temporal resolution. For this, during a three-week campaign in Norway in July 2017, sulfur dioxide (SO2), a nearly passive tracer, was artificially released in continuous plumes and nearly instantaneous puffs from a 9 m high tower. Column-integrated SO2 concentrations were observed with six UV SO2 cameras with sampling rates of several hertz and a spatial resolution of a few centimetres. The atmospheric flow was characterised by eddy covariance measurements of heat and momentum fluxes at the release mast and two additional towers. By measuring simultaneously with six UV cameras positioned in a half circle around the release point, we could collect a data set of spatially and temporally resolved tracer column densities from six different directions, allowing a tomographic reconstruction of the 3-D concentration field. However, due to unfavourable cloudy conditions on all measurement days and their restrictive effect on the SO2 camera technique, the presented data set is limited to case studies. In this paper, we present a feasibility study demonstrating that the turbulent dispersion parameters can be retrieved from images of artificially released puffs, although the presented data set does not allow for an in-depth analysis of the obtained parameters. The 3-D trajectories of the centre of mass of the puffs were reconstructed enabling both a direct determination of the centre of mass meandering and a scaling of the image pixel dimension to the position of the puff. The latter made it possible to retrieve the temporal evolution of the puff spread projected to the image plane. The puff spread is a direct measure of the relative dispersion process. Combining meandering and relative dispersion, the absolute dispersion could be retrieved. The turbulent dispersion in the vertical is then used to estimate the effective source size, source timescale and the Lagrangian integral time. In principle, the Richardson–Obukhov constant of relative dispersion in the inertial subrange could be also obtained, but the observation time was not sufficiently long in comparison to the source timescale to allow an observation of this dispersion range. While the feasibility of the methodology to measure turbulent dispersion could be demonstrated, a larger data set with a larger number of cloud-free puff releases and longer observation times of each puff will be recorded in future studies to give a solid estimate for the turbulent dispersion under a variety of stability conditions.

Project Sagebrush: Revisiting the Value of the Horizontal Plume Spread Parameter σy

AbstractThe first phase of an atmospheric tracer experiment program, designated Project Sagebrush, was conducted at the Idaho National Laboratory in October 2013. The purpose was to reevaluate the results of classical field experiments in short-range plume dispersion (e.g., Project Prairie Grass) using the newer technologies that are available for measuring both turbulence levels and tracer concentrations. All releases were conducted during the daytime with atmospheric conditions ranging from neutral to unstable. The key finding was that the values of the horizontal plume spread parameter σy tended to be larger, by up to a factor of ~2, than those measured in many previous field studies. The discrepancies tended to increase with downwind distance. The values of the ratio σy/σθ, where σθ is the standard deviation of the horizontal wind direction, also trend near the upper limit or above the range of values determined in earlier studies. There was also evidence to suggest that the value of σy began to be independent of σθ for σθ greater than 18°. It was also found that the commonly accepted range of values for σθ in different stability conditions might be limiting, at best, and might possibly be unrealistically low, especially at night in low wind speeds. The results raise questions about the commonly accepted magnitudes of σy derived from older studies. These values are used in the parameterization and validation of both older stability-class dispersion models as well as newer models that are based on Taylor’s equation and modern PBL theory.

A new Lagrangian method for modelling the buoyant plume rise

A new method for the buoyant plume rise computation is proposed. Following Alessandrini and Ferrero (Phys A 388:1375–1387, 2009) a scalar transported by the particles and representing the temperature difference between the plume and the environment air is introduced. As a consequence, no more particles than those inside the plume have to be released to simulate the entrainment of the background air temperature. A second scalar, the vertical plume velocity, is assigned to each particle. In this way the entrainment is properly simulated and the plume rise is calculated from the local property of the flow. The model has been tested against data from two laboratory experiments in neutral and stable stratified flows. The comparison shows a good agreement.Then, we tested our new model against literature analytical formulae in a simple uniform neutral atmosphere, considering either the case of a single plume or the one of two plumes from adjacent stacks combining during the rising stage. Finally, a comparison of the model against an atmospheric tracer experiment (Bull Run), characterized by vertically non-homogeneous fields (wind velocity, temperature, velocity standard deviations and time scales), was performed. All the tests confirmed the satisfactory performance of the model.

Source Reconstruction of Unknown Model Parameters in Atmospheric Dispersion Using Dynamic Bayesian Inference

A source reconstruction capability driven by time-evolving data is tried out by coupling the observed data and predictive model through dynamic Bayesian inference to obtain solutions to inverse problem. Solutions are determined by posterior probability distributions describing unknown model parameters and the Markov Chain Monte Carlo method with the Metropolis-Hastings sampling algorithm is employed to obtain the solutions. The posterior distributions of model parameters are obtained by performing stochastic sampling by the likelihood function test indicating the agreements between the measurements and the predictions from Gaussian plume model. The Yonggwang atmospheric tracer experiment in Korea is selected to testify the source reconstruction algorithm. The simulation has shown that the posterior modes of the release point and the released source rate for this experiment obviously converged to their true values.

Convergence Monitoring of Markov Chains Generated for Inverse Tracking of Unknown Model Parameters in Atmospheric Dispersion

The dependency within the sequential realizations in the generated Markov chains and their reliabilities are monitored by introducing the autocorrelation and the potential scale reduction factor (PSRF) by model parameters in the atmospheric dispersion. These two diagnostics have been applied for the posterior quantities of the release point and the release rate inferred through the inverse tracking of unknown model parameters for the Yonggwang atmospheric tracer experiment in Korea. The autocorrelations of model parameters are decreasing to low values approaching to zero with increase of lag, resulted in decrease of the dependencies within the two sequential realizations. Their PSRFs are reduced to within 1.2 and the adequate simulation number recognized from these results. From these two convergence diagnostics, the validation of Markov chains generated have been ensured and PSRF then is especially suggested as the efficient tool for convergence monitoring for the source reconstruction in atmospheric dispersion.

Atmospheric Dispersion from a Point Source in Four Southern Pine Thinning Scenarios: Basic Relationships and Case Studies

An atmospheric tracer experiment using SF6 was designed to assess changes in the dispersive environment in the trunk space of a southern pine forest through four thinning regimes. Over 6000 mean half-hourly tracer samples were collected and analyzed along with a high-frequency time series of tracer concentration sampling at 1 Hz over the course of the trials. The experimental plot was thinned in four stages, from a state of dense boles and thick understory, >32.1 m2 ha-1 (140 ft2 ac-1) basal area, to a final basal area of 16.1 m2 ha-1 (70 ft2 ac-1) with understory removed. In this study, plume dilution in the unthinned stand followed previously observed relationships; however, thinned stands deviated from expectations. The in-canopy atmosphere was largely coupled with the above-canopy atmosphere once a basal area of 23.0 m2 ha-1 (100 ft2 ac-1) or lower was attained, so additional tree removal had less effect in changing the in-canopy environment. Dispersion exhibited surprisingly strong, near-linear relationships with stand density.

長距離逆大気輸送計算による放出源情報推定法

A new method to estimate the location and the relative rate of an accidental atmospheric release from the input of environmental monitoring data such as concentration of contaminants has been developed and its performance has been verified using the long-range atmospheric tracer experiment data. This method employs an inverse transport calculation of a mass of marker particles released from monitoring points. The source terms are evaluated from the statistics on the position of marker particles. The objective domain is about 1, 000 km or more from a release point. The verification showed that the location and the rate of release were fairly estimated by the method. It was also pointed out that the combination of this method with a normal atmospheric dispersion simulation would be effective.

Optimal sampler siting for atmospheric tracer experiments taking into account uncertainties in the wind field

Abstract The problem of sampling sites for atmospheric tracer experiments were considered in Federov and Pitorvranov (working paper WP-85-65, International Institute for Applied Systems Analysis, Laxenburg, Austria, 1988). There it was assumed that the wind direction during an experimental tracer release could be accurately predetermined and would remain constant for the duration of the experiment. In general, this assumption of a constant wind field is not met. In this work we develop an approach which overcomes this deficiency. The monitoring network design problem is considered for cases which include prior uncertain wind fields during a designed experiment.

Tagging In-Stack Suspended Particles from a Coal-fired Power Plant with an Enriched Isotopic Tracer

A device was constructed for tagging coal fly-ash particles with enriched isotopes of Nd for use in atmospheric tracer experiments by thermally degrading vapor of the 2,2,6,6-tetramethyl 3,5-heptanedione chelate of the metal in the presence of fly-ash laden flue gas. Microanalysis measurements of individual fly-ash particles verify the surface residence of the tracer material and show that particle surfaces are devoid of individual Nd particles. The prototype device was used to release 148Nd- and 145Nd-tagged fly-ash particles for an urban-scale field test at isotope delivery rates of 25–54 mg/h.

Morning Transition Tracer Experiments in a Deep Narrow Valley

Abstract Three sulfur hexafluoride atmospheric tracer experiments were conducted during the post-sunrise temperature inversion breakup period in the deep, narrow Brush Creek Valley of Colorado. Experiments were conducted under clear, undisturbed weather conditions. A continuous elevated tracer plume was produced along the axis of the valley before sunrise and the behavior of the plume during the inversion breakup period was detected down-valley from the release point using an array of radio-controlled sequential bag samplers, a vertical SF6 profiling system carried on a tethered balloon, two portable gas chromatographs operated on a sidewall of the valley, and a continuous real-time SF6 monitor operated from a research aircraft. Supporting meteorological data came primarily from tethered balloon profilers. The nocturnal elevated plume was carried and diffused in down-valley flows. After sunrise, convective boundary layers grew upward from the sunlit valley surfaces, fumigating the elevated plume onto the ...

Antarctic atmospheric tracer experiments

Although the Antarctic circulation cell is a statistical construct, its ability to transport trace gases and aerosols to the continent has been discerned experimentally by the use of deuterated methane atmospheric tracers. Atmospheric tracer experiments were conducted in 1984 to study transport from the mid‐latitudes of the southern hemisphere to Antarctica. The tracer was transported to the polar plateau within a few days following tracer releases that took place in the summer and spring. However, in winter, poleward transport of the tracer was inhibited by the winter circumpolar vortex. The tracer concentration pattern was consistent with a “lumpy, streaky” distribution produced by a numerical model of global circulation.

Estimating the Tritiated Hydrocarbon Decontamination Factor by Heavy Methane

As part of the start up of Los Alamos National Laboratory’s new tritium-handling facility, the efficiency of a catalytic oxidation tritium decontamination system was investigated using deuterated methane. The tests were performed during the start up of the facility to confirm the operability of the system before introducing tritium and to provide a baseline for comparison. Techniques and instruments normally used for atmospheric tracer experiments using deuterated methane were applied virtually without modification. The sensitivity of this method allowed preliminary checks at the sub-ppm (v/v) level.

The transport and dispersion of airborne contaminants in boundary layers over the ocean and an isolated island cape

A series of sixteen atmospheric tracer experiments using sulfur hexafluoride (SF6), chemical smoke and meteorological balloons was conducted to explore the transport of airborne contaminants in the boundary layer over the ocean surface and in the separating boundary layer over an isolated island cape. The immediate objective of the tests was to determine the impact of local pollutant sources on a background air quality sampling program conducted in the South Pacific from elevated towers on Tutuila Island, American Samoa. In addition to satisfying this objective, the tests are of interest in that they illustrate the local behavior of pollutants in a complex natural atmospheric flow. Offshore tracer tests indicated that the crosswind dispersion of pollutants over the ocean surface can be approximately modeled using the simple Gaussian plume model. The observed crosswind dispersion of the tracer corresponded to that expected under neutrally stable atmospheric conditions, consistent with the near equilibration of the ocean surface and air temperature in the South Pacific. Local, or near-field, tests indicated that tracer released into the wake downwind of the leading edge of the cape mixed rapidly to a height of about 8 m above the surface (i.e., 30–40% of the cape height). Due to decoupling between the boundary layer over the cape and the freestream flow, however, very little of the tracer was observed above this height. This suggests that the impact of local pollutant sources (i.e., on the cape) would be minimized if the proposed sampling towers were elevated significantly above an 8 m altitude (e.g., twice that height).

Overwater Atmospheric Diffusion: Measurements and Parameterization

Abstract A series of ten atmospheric tracer experiments provided 62 hours of overwater atmospheric dispersion data. Sulfur hexafluoride (SF6) was released as the tracer gas at a height of 13 m from a ship positioned about 7 km off the central California coast in the vicinity of Pismo Beach. Surface and upper air meteorological measurements were made at the release point and near the shoreline. Horizontal crosswind tracer concentration profiles were obtained at the shoreline, both at the surface and multiple levels aloft through the mixed layer. Tracer data were analyzed to determine the lateral diffusion parameter σy for hourly periods as the best fit to a Gaussian distribution. The vertical diffusion parameter σz was determined from the vertical profile of the hourly crosswind-integrated tracer concentration. Four classification schemes of atmospheric stability were intercompared and showed wide variation in their estimates. The lateral diffusion measurements are reasonably well gratified by three of the...

Sensitive determination of perfluorocarbon tracers in air by intermediate trapping and GC‐ECD analysis

AbstractThis paper reports on the development of a simple method for the determination of two perfluorinated hydrocarbons (C7F14 and C8F16) in air down to 0.2 ng/m3, for long range atmospheric tracer experiments. The organic vapors are adsorbed on graphitized carbon black, desorbed thermally and determined by capillary GC‐ECD at subambient temperature. Optimization of the experimental conditions is described. The tracers were tested in a field experiment where SF6 was also released and the agreement was satisfactory.

A literature survey on tracer experiments for atmospheric dispersion modelling studies

After the boom of purely theoretical work on the dispersion of pollutants in the atmosphere, considerable efforts are now invested in the experimental measurement of atmospheric dispersion and in model validation using tracer techniques. The actual state of the art is sketched by a literature survey. The available references are classified under four headings: (i) experimental papers describing sampling and analytical possibilities; (ii) qualitative atmospheric tracer experiments without mathematical treatment; (iii) tracer experiments for the determination of model parameters and (iv) tracer experiments for model validation. SF 6 is now the most popular tracer but perfluorocarbons are gaining interest for long-range dispersion experiments. Among the several dispersion parameter sets for the bi-Gaussian dispersion theorem, only few are strongly based on systematic tracer experiments. Many papers describe tracer dispersion experiments, but the comparison of measured with calculated concentrations for model validation is a research area where much work remains to be done.

Technique for Elevated Release of Sulfur Hexafluoride Tracer

Study of the dispersion of atmospheric pollutants has benefited greatly in the past from the use of artificial tracers. The study described in this paper used tethered balloons which carry one end of a hose aloft, through which a gaseous tracer can be dispensed. From the field tests it was concluded that the tandem balloon system is useful in atmospheric tracer experiments where a single balloon has insufficient lift to provide a release at the desired elevation. The SF/sub 6/ release system proved to be portable, easy to use, and suitable for simulating continuous elevated pollutant releases. 3 figures. (DP)

Characterization of the transport and dispersion of pollutants in a narrow mountain valley region by means of an atmospheric tracer

Three atmospheric tracer experiments using sulfur hexafluoride (SF6), were conducted in a narrow mountain valley from 29 January–3 February 1982. These tests were performed in order to characterize the transport and dispersion of airborne pollutants around Telluride, Colorado which lies near the head of the San Miguel Valley. Particular attention was given to the influence of flow reversals upon pollutant dispersion, for which adequate numerical simulation is not yet available. Data from surface wind stations, pilot balloons and from an acoustic sounder were used to characterize the local meteorology. In this case, an upslope flow followed by a downslope drainage is required for emissions from a site on the slope to reach the upper valley about 10 km away. On the other hand, a downvalley flow followed by an upslope flow is required for emissions from the upper valley to reach the slope site. Certain aspects of the transport and dispersion characteristics associated with the mesoscale winds in the area appear to be relatively insensitive to changes in the synoptic winds. For example, even though the synoptic wind patterns in Tests One and Two were different, the 24-h average concentrations in the upper valley were found to be about 15 and 17 (kg-mole) −1h −1, respectively at the slope site. Test Three involved releasing the tracer from Telluride. The 24-h average concentration of tracer at Telluride was used, along with an estimate of the particulate emission rate, to predict the average ambient concentration of total suspended particulates. The value predicted was 71 μgm −3, which is in excellent agreement with the measured value of 63 μgm −3. After the downvalley flow gave way to the midday upslope flow, tracer concentrations were measured along a ski lift. The tracer concentration decreased linearly with increasing distance up the slope. Estimates of concentrations based upon the Gaussian model, (the parameters of which were determined from meteorological data), were in general higher than those observed. In addition to allowing direct prediction of impacts of pollutants emitted within this region, these data can be used to test the validity of numerical models.

Uncertainties Associated with the Estimation of Mass Balances and Gaussian Parameters from Atmospheric Tracer Studies

Data resulting from two atmospheric tracer experiments in the land-sea breeze winds in Los Angeles, CA are used to compare the observed and released amounts of tracer (a mass balance). The mass balance calculation indicated that essentially all of the tracer transported to sea during the land breeze was transported back across the shore during the subsequent sea breeze. A methodology for calculating a mass balance and the associated uncertainties is presented. The experimental and calculation procedures presented allowed mass balance estimates with less uncertainty than is present in individual measurements of concentration or mixing height. Similarly, a methodology for calculating dispersion parameters for the gaussian plume model from tracer data is discussed and applied to the results of two atmospheric tracer studies conducted during the afternoon sea breeze in the Santa Barbara Channel of California. The method presented involves the integral definitions of the statistical quantities. By considering only tracer concentrations greater than 10% of the maximum concentration, and by considering sufficiently many data points, the uncertainty associated with the parameter estimation was again less than the relative uncertainties in any individual data point. These studies were primarily designed to relate the uncertainties in estimates of mass balances and in estimations of gaussian parameters to the uncertainties inherent within field data.

Atmospheric transport of visibility degrading pollutants into the California mojave desert

Three atmospheric tracer experiments using SF 6 and fine aerosol measurements were conducted in California to determine the relative impact of pollutant sources in the San Fernando Valley area of Los Angeles and the southern San Joaquin Valley on visibility in a portion of the Mojave Desert. Dilution ratios calculated for SF 6 and various gaseous and aerosol chemical species were used to indicate atmospheric transformation processes between source and receptor. The evolution of the aerosol sulfur mass distribution resulting from transport and transformation was measured. The SF 6 data were compared with predictions based upon the Gaussian dispersion model. SF 6 released in the San Fernando Valley was found to impact the southern Mojave Desert including the towns of Palmdale and Adelanto. SF 6 released at Oildale in the southern San Joaquin Valley was found to directly impact the northern Mojave Desert including the towns of Mojave and China Lake. Some SF 6 released in the San Joaquin Valley was also detected in the southern Mojave Desert. SF 6 was found to be diluted by factors of only 2–3 during passage over the mountains separating the source and receptor areas. The SF 6 dispersion during the San Fernando Valley experiment could be modeled with the Gaussian plume model if the experimentally determined mixing height, transport speed and plume trajectory were used, and the stability class was chosen to give good agreement with the data. A simple Gaussian plume model could not provide an adequate description of the San Joaquin Valley test because of the complexities of the wind reversal that occurred during the transition from morning to afternoon flow conditions during this test. Dilution ratios for conserved fine aerosols between Oildale and China Lake were found to be about 3. in excellent agreement with the SF 6 data. The timing of the diurnal degradation in visibility at China Lake was found to coincide with the arrival of SF 6, thus indicating that the southern San Joaquin Valley was the source of visibility degrading aerosol. The aerosol sulfur mass distribution was found to be essentially conserved between Oildale and China Lake and substantially different from Los Angeles-Palm Springs sulfur mass distributions. Our data indicate that pollutants from both the southern San Joaquin Valley and the Los Angeles Basin can impact the Mojave Desert during their transport eastward by the predominantly westerly summertime winds; consequently, both “plumes” should be taken into account when considering the impact of southern California pollutants upon the southwestern United States.