True Release Rate Research Articles

Evaluating the Performance of Soil Flux Surveys and Inversion Methods for Quantification of CO2 Leakage

Understanding the near surface migration patterns and rates of efflux of CO2 is important for developing effective monitoring and verification programs for the geological storage of CO2. Soil flux surveys are a well-established technique for characterising surface CO2 emission sources from controlled release sites, CO2 storage sites or natural CO2 seeps. The performance of four interpolation methods; arithmetic mean (AM), two minimum variance unbiased estimators (MVUE), and a newly developed geostatistical cubic surface were evaluated using 21 soil flux surveys conducted over two controlled release experiments in 2012 and 2013, at the Ginninderra controlled release facility, Australia. Data was binned to approximate a regular sampling grid for improved performance of the whole-of-field AM and MVUE averaging techniques. The AM and MVUE methods were highly sensitive to deviations in the statistical distribution of the data, and performed inconsistently across the two experiments. These two methods proved ill-suited for application to CO2 leak quantification due to their inflexible sampling and distribution requirements. The cubic technique provided the best net emission estimates across both experiments, and when applied at different bin sizes, estimating the true release rate to within 20% for the 2012 experiment and 45% below the release rate for the 2013 experiment. The cubic method is well-suited for CO2 leak quantification because it is not limited by assumptions of the data's spatial or statistical distribution. Net H2O emissions of 29 kg/d were observed coincident with the high CO2 flux zones in the field. The interpolation methods were applied with similar results on soil flux surveys taken from a natural seepage site in Qinghai, China. Gravity currents appear to describe the observed soil flux and soil gas behavior at Ginninderra, i.e. the observed lateral migration of CO2 in the subsurface. Subsurface migration was also strongly influenced by the relative depth of the groundwater. Thus the low water table and greater vadose zone in the 2013 experiment is suspected to facilitate greater lateral CO2 migration and explain the poor closure of the CO2 balance.

Reconstruction of an atmospheric tracer source in an urban‐like environment

AbstractThis study describes a methodology combining a recently proposed renormalization inversion technique with a building‐resolving computational fluid dynamics (CFD) approach for source retrieval in the geometrically complex urban regions. It presents the first application of the renormalization inversion approach to estimate an unknown continuous point release in real situations at an urban scale. The renormalization inversion approach is based on an adjoint source‐receptor relationship and is purely deterministic in nature. The source parameters (i.e., source location and release rate) are reconstructed from a finite set of point measurements of concentration acquired from some sensors and the adjoint functions computed from a CFD model fluidyn‐PANACHE that is able to represent the geometric and flow complexity inherent in the urban regions. The inversion procedure is evaluated for a point source reconstruction using measurements from the Mock Urban Setting Test (MUST) field experiment. Source reconstructions are performed for 20 trials of the MUST experiment of a continuous point release in an idealized urban geometry consisting of a regular array of shipping containers. The steady state flow fields are computed by solving the three‐dimensional Reynolds‐averaged Navier‐Stokes equations by using a finite volume scheme. Then, in each MUST trial adjoint functions are obtained and used for the source identification. Inversion results are presented with both synthetic and real measurements in various atmospheric stabilities varying from neutral to stable and very stable conditions. With real concentration measurements, the point source is retrieved within an average Euclidean distance of 14.6 m from the actual source location. The estimated source intensity is overpredicted by an average factor of 1.37 of the true release rate. In a posterior uncertainty analysis with 10% random noise in measurements, it is demonstrated that standard deviation in the location error and release strength, respectively, varies by 5.22 m and ∼21% from their mean value for all 20 trials. A sensitivity analysis shows that the use of nonzero measurements helps in reducing the uncertainties involved in the source reconstruction. The source reconstruction results in various stability conditions exhibit the reliability of the renormalization inversion methodology coupled with the CFD approach in an urban area. The present methodology can be used by emergency regulators as a tool to detect the unknown accidental or deliberated releases in the complex urban environments.

Measurement of fugitive volatile organic compound emissions from a petrochemical tank farm using open-path Fourier transform infrared spectrometry

Fugitive emission of air pollutants is conventionally estimated based on standard emission factors. The Vertical Radial Plume Mapping (VRPM) technique, as described in the US EPA OTM-10, is designed to measure emission flux by directly monitoring the concentration of the plume crossing a vertical plane downwind of the site of interest. This paper describes the evaluation results of implementing VRPM in a complex industrial setting (a petrochemical tank farm). The vertical plane was constructed from five retroreflectors and an open-path Fourier transform infrared spectrometer. The VRPM configuration was approximately 189.2 m in width × 30.7 m in height. In the accompanying tracer gas experiment, the bias of the VRPM estimate was less than 2% and its 95% confidence interval contained the true release rate. Emission estimates of the target VOCs (benzene, m-xylene, o-xylene, p-xylene, and toluene) ranged from 0.86 to 2.18 g s−1 during the 14-day field campaign, while estimates based on the standard emission factors were one order of magnitude lower, possibly leading to an underestimation of the impact of these fugitive emissions on air quality and human health. It was also demonstrated that a simplified 3-beam geometry (i.e., without one dimensional scanning lines) resulted in higher uncertainties in the emission estimates.

Phosphorus release from coated monoammonium phosphate: Effect of coating thickness, temperature, elution medium, soil moisture and placement method

Coating fertilizer granules with a polymer slows the release of nutrients over a long period of time, so that the fertilizer uptake by plants may be enhanced. Two laboratory experiments were conducted to determine the effects of coating thickness, temperature, soil moisture, and placement method on the release rate of P from coated monoammonium phosphate (MAP) in soil; to compare the release rate of P from coated MAP in soil and in water; and to evaluate different kinetic equations for simulating the release of P from coated MAP. In exp. 1, release of P from 10 pre-weighed granules of a non-coated MAP and three polymer-coated MAP fertilizers (Coated I, 4%; Coated II, 4.5%; and Coated III, 5%) was determined in water at 10 and 23°C. In exp. 2, release of P from the four MAP fertilizers in soil was determined at two temperatures (10 and 23°C), two moisture levels (90 and 60% field capacity) and two placement methods (incorporation and banding). Four kinetic equations, i.e., simple Elovich, Parabolic diffusion, Power function, and First order kinetics, were evaluated to simulate the release of P from coated MAP. Activation energy of P release was calculated using the P release versus ln time plots of the simple Elovich equation. The release rate of P from coated MAP was strongly affected by coating thickness and temperature but was not affected by method of P placement and soil water content. The release of P from coated MAP was slower in soil than in water, and it decreased markedly with increasing thickness of polymer coating on MAP, whereas it increased with increasing temperature. The simple Elovich equation best described the release of P from coated MAP in both water and soil. The activation energy was not affected by elution medium and coating thickness but it was lower at the higher temperature. In conclusion, the test of P release rate from coated MAP in water may not represent the true release rate of P from coated MAP in soil, as it is influenced by elution medium, temperature and coating thickness. The simple Elovich equation best described the P release kinetics from coated MAP in soil and in water. Key words: Coating thickness, monoammonium phosphate, P release rate in water and soil, P release kinetics, placement method, soil moisture content, temperature

Method for evaluating drug release from liposomes in sink conditions

An in vitro method was developed for the evaluation of the drug release from disperse systems, such as liposomes, under sink conditions. Determination of in vitro release of lipophilic drugs from liposomes requires a dissolution medium that maintains sink conditions without damaging the lipid membrane and a method to separate the released drug from the liposomal drug. We propose a new in vitro technique for the evaluation of drug release from liposomes using a hydrophilic β-cyclodextrin derivative in the dissolution medium to maintain sink conditions. A liposomal drug dispersion was placed in a magnetically stirred dialysis bag (Mw cut-off 300 000) containing cyclodextrins to provide sink conditions. The released drug was sampled from the outside of the bag. Release of hydrocortisone and budesonide from different multilamellar liposomes was measured. True release rate was evaluated from the release data of liposomal and free drug from the dialysis bags, respectively. Release of steroids from the liposomes was relatively fast, but they were retained longer in gel-phase, distearoyl- l- α-phosphatidylcholine (DSPC) liposomes than in liquid-phase, l- α-phosphatidylcholine (EPC) liposomes. Leakage of encapsulated calcein from the liposomes was not affected by cyclodextrins suggesting that they do not disturb the structure of the lipid bilayers. This method is capable of distinguishing different true release rates of drugs from colloidal carriers and it is easy to perform.

PH‐stat methodology in continuous monitoring of the kinetics of hydrolysis of phosphate esters catalysed by alkaline phosphatase from human placenta: Limitations, advantages and theoretical aspects

AbstractThe appropriateness of pH‐stat methodology in the dynamic monitoring of the kinetics of hydrolysis of phosphate esters catalysed by alkaline phosphatase (from human placenta) has been studied. This methodology involves autotitration of the H+ released or consumed during a given reaction time. The lack of specificity of the method, titrating the total H+, together with the known effect of the dissolution of environmental CO2 on the reacting system, giving rise to carbonic acid, implies an overtitration of the H+ released in the hydrolysis reaction. Because of this, parallel to each series of reaction kinetics, the dissolution kinetics of environmental CO2 under working conditions are quantified with suitable blanks, thus enabling one to subtract them from the global kinetics of the release of H+. Although no background buffers are added to the reacting system in order to maintain a constant pH, the buffering capacity of the system itself obliges one to quantify it by calibrations in order to calculate the true release rate of H+ in the reaction. These two principal limitations of the pH‐stat methodology, the dissolution of environmental CO2 and the inherent buffering capacity of the system, can be partially mitigated by working within an inert atmosphere of N2 and having a good knowledge of the acid/base characteristics of the reagents and reaction products, which together will permit the choice of a working pH range in which the second limitation will be negligible. Having studied theoretically the acid/base balances of the system in reaction, it is concluded that optimum working conditions for the pH‐stat methodology are between pH 8·5 and 11·0, since over this pH range the buffering capacity is null (thus eliminating the need for calibrations) and the stoichiometry of H+ (nH+) is close to unity. These theoretical predictions have been confirmed experimentally with calibrations and measurements of nH+ at different pH values.

Effect of Varying Levels of Tapazole on Thyroidal-I131 Uptake in New Hampshire Pullets

Abstract IN THE routine determination of thyroxine secretion rate (TSR) in fowls, 0.05% tapazole (methimazole) has been added to the ration to prevent recycling of I131 resulting from the metabolism of thyroxine-I131. This has been done to obtain the true release rate of thyroidal-I131. In chicks under 4–6 weeks of age, the release rate is rapid and goitrogens are not necessary but in older birds the release rate generally slows down and prevention of recycling of I131 is necessary to indicate the end-point of TSR determination. At the level of 0.05% tapazole used up to this time, it has been noted that tapazole even with thyroxine administration tended to reduce egg production and feed consumption and birds sometimes began to molt. It has been suggested, also, that goitrogens may influence thyroxine secretion. Sell and Balloun (1960) reported an increased occurrence of capillary rupture in the thyroids of cockerels treated…