Gas flux measurement

Denmead, O. T. (1995). Novel micrometeorological methods for measuring trace gas fluxes. Phil. Trans. Roy. Soc. Loud. A. 351,383-396. Denmead, O. X, Leuning, R., Griffith, D. W. X, and Meyer, C. P. (1999). Some recent developments in trace gas flux measurement techniques. In Approaches to Scaling of Trace Gas Fluxes in Ecosystems. (A. F. Bouwman, Ed.), pp. 69-84. Elsevier, Amsterdam. 

ILM Gas Flux Measurement. Several methods have been used to measure fluxes through ILMs a transient pressure measurement (24), a radioisotope tracer technique ( ), and a flow cell techniqueTsO, 34). 

A key issue in the research of our ecosystem and in atmospheric studies today is the ability to quantify even small concentrations of trace gases, and follow their evolution from a source to their final destination. For biosphere-atmosphere or air-sea exchange, trace gas flux measurements based on the eddy correlation technique in addition to high temporal resolution (sometimes less than 1 s) is required. Of the many... 

An important question to answer once an eruption is underway is when will it stop. The first sign may be the cessation of low-frequency seismicity, indicating that volatiles are no longer present in the system, which may be confirmed with gas flux measurements. More significant may be the occurrence of VT earthquakes at depth with fault-plane solutions consistent with magma withdrawal (Roman et al. 2006). Geodetic data may also indicate deflation of the volcanic edifice. 

Rinne, H. J. I., Guenther, A., Wameke, C. et al. (2001) Disjunct eddy covariance technique for trace gas flux measurements. Geophys. Res. Lett. 28, 3139. 

Fig. 1. Rates of CO2 assimilation, A (/miol s ) leaf conductance, g (mol m s ) intercellular partial pressure of CO2, Pi (Pa) soil water potential and leaf water potential, xp (MPa) during gas-exchange measurements of a 30-day-old cotton plant, plotted against day after watering was withheld. Measurements were made with 2 mmol m sec" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure difference between leaf and air (S.C. Wong, unpublished data).

The air-sea fluxes are inversely proportional to the thickness of the thin film. From the measurement of gas fluxes and concentration gradients, oceanographers have inferred that the stagnant-film thickness ranges from 10 to 60 gm. As mentioned earlier, direct flux measurements are difficult to make at sea, especially in the presence of... 

The integral permeability coefficient P may be determined directly from permeation steady-state flux measurements or indirectly from sorption kinetic measurements 27 521 activity is usually replaced by gas concentration or pressure (unless the gas deviates substantially from ideal behaviour and it is desired to allow for this) and a<>, ax (p0, Pi) are the boundary high and low activities (pressures) respectively in a permeation experiment, or the final (initial) and initial (final) activities (pressures) respectively in an absorption (desorption) experiment. 

We chose to use a modernized version of the manometric measuring technique both in our earlier work and in the present experiments. This approach offered good flexibility in that the electronic manometers used to monitor the gas flux respond to a wide variety of gases. It is also possible to calibrate the apparatus reliably using existing standards. By completely computerizing the measurement process (6) we were able to provide... 

Failing to incorporate soil-gas advection induced by barometric pumping into gas-phase subsurface transport models may, under certain conditions, under predict contaminant flux to the atmosphere. As previously described, Smith et al. (1996) compared TCE vapor fluxes measured with a chamber device to TCE in groundwater being removed by a pump-and-treat system and discharge into a surface-water receiving body at the same site. These researchers found VOC removal rates by flux to the atmosphere comparable in magnitude to both of the other attenuation pathways. 

The permeability of gases through membranes is most commonly measured in Barrer, defined as 10-10 cm3(STP)/cm2 s cmHg and named after R.M. Barrer, a pioneer in gas permeability measurements. The term ji/ pio — pit), best called the pressure-normalized flux or permeance, is often measured in terms of gas permeation units (gpu), where 1 gpu is defined as 10 6 cm3(STP)/cm2 s cmHg. Occasional academic purists insist on writing permeability in terms of mol m/m2 s Pa (1 Barrer = 0.33 x 10-15 mol m/m2 s Pa), but fortunately this has not caught on. 

Devol, A.H. (1991) Direct measurement of nitrogen gas fluxes from continental shelf sediments. Nature. 349 319-321. 

Nowicki, B.L. (1994) The effect of temperature, oxygen, salinity, and nutrient enrichment on estuarine denitrification rates measured with a modified nitrogen gas flux technique. Estuar. Coastal Shelf Sci. 38, 137-156. 

Both cold and hot inert gas pressure tests were performed on samples of brazed cermet membranes in advance of hydrogen flux measurements in order to ascertain the integrity of the Inconel 600-to-cermet seal under high temperature and pressure conditions. The procedure used in these tests has been described elsewhere [Rothenberger etal., 1999]. 

A study was carried out into the potential recovery of plasticiser and solvent from waste PVC plastisols using a ceramic multi-bore crossflow tube filter. The procedure employed to perform the test sequence involved clean water flux measurement, media acclimatisation, optimisation trial, concentration run, cleaning trial and final water flux measurement. Permeate samples were analysed using gas chromatography and compared with standards of diisononylphthalate(DINP)/white spirit mixtures. The ceramic membrane successfully recovered a clear mixture of DINP and white spirit. 

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