Abstract. Estimates of methane (CH4) emissions from slurry tanks or lagoons in the past have been made primarily by using chamber techniques, which are point specific and interfere with conditions at the slurry-atmosphere interface. This study is based on the use of sulphur hexafluoride (SF6) as a tracer gas to estimate CH 4 transport from the slurry

Abstract. Comparisons of observations of concentration or flux from platforms at various heights, such as tower and aircraft, must take into account differences in the location and extent of upwind surface source or sink areas which affect the individual observations, with their physical and biological characteristics. Such "footprint" estimates are based on solutions of the diffusion/advection equation which have not previously been evaluated over a boreal ecosystem. In order to adjust an analytical footprint model within the surface layer above forest canopies typical for the Boreal Ecosystem-Atmosphere Study (BOREAS) sites, 29 tracer gas release experiments were carried out between August 30 and September 9, 1994, at three tower sites in the northern study area (NSA). Sulphur hexafluoride (SF6) was released from point sources at various upwind distances from the towers under various meteorological, terrain, and release conditions. Wind, temperature, and stability parameters, during each release period, were used as input into calculations of vertical concentration profiles sampled at the towers, based on a three-dimensional diffusion model. Predictions of concentration profiles, or back calculation of source strength from observed profiles, were in good agreement with observed concentrations or actual release rates, respectively. The diffusion model was then used to compute footprint estimates for stable to unstable conditions, for tower and aircraft-based observation platforms. They show spatially constrained footprints in the surface layer, due to effective vertical coupling, so observations from towers and low-flying aircraft must be expected to be very site specific, and scaling up to larger areas will have to be done with careful consideration of surface mosaics. Our study also included footprint estimates made for airborne observations above the surface layer, based on large-eddy simulations over "BOREAS-like" terrain, for boundary layer structures comparable to those observed in BOREAS. They document the progressive decoupling of airborne observations from the surface features at these heights.

Riddle, C. 2006. Towards standards for measuring greenhouse gas fluxes from agricultural fields using instrumented towers. Can. J. Soil Sci. Can. J. Soil Sci. 86: 373-400. This is a discussion of the available technology for measuring turbulent fluxes using instrumented towers. This review focuses on the flux measurements of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) for agricultural systems and the development of standards and protocols for measuring them. Agroecosystems present unique challenges because they undergo large leaf area index (LAI) and canopy architecture changes in a relatively short period of time (i.e., months) coupled with the fact that many of the greenhouse gas sources are diffuse. This review examines all aspects of the theory and application of the micrometeorological techniques, with focus on the flux gradient, eddy accumulation and eddy covariance techniques. Instrument placement, sensor response and noise characteristics are also explored. Innovative applications of micrometeorological methods are discussed for closed-and open-path trace gas sensors and commonly used meteorological instrumentation. The use of fastresponse single-pass optical tunable diode laser (i.e., CH 4 , N 2 O) and infrared gas analyzers (i.e., CO 2 , H 2 O) is described. Consideration is also taken of the trace gas sensors' flow system design, mixing ratio measurement, and data acquisition and reduction requirements for micrometeorological flux measurement. Procedures are outlined for the meteorological instrumentation necessary for eddy covariance-based energy budget measurement including ultrasonic anemometry. Les écosystèmes agricoles présentent des contraintes spécifiques du fait que l'indice foliaire et l'architecture du couvert végétal subissent d'importants changements durant la saison de croissance (quelques mois) et que la plupart des sources de gaz à effet de serre sont diffuses. Les auteurs examinent les principes et les applications de la micrométéorologie sous toutes leurs facettes, en insistant sur les techniques des gradients de flux, d'accumulation des tourbillons et la covariance des fluctuations. Ils abordent aussi l'installation des instruments, la sensibilité des capteurs et les caractéristiques du bruit de fond. Les auteurs présentent des applications novatrices de la micrométéorologie pour les capteurs de gaz à l'état de traces à parcours ouvert et fermé ainsi que des instruments employés couramment en météorologie. Ils décrivent l'utilisation de diode laser accordable à parcours optique unique et à réponse rapide (pour le CH 4 et le N 2 O) et d'analyseurs de gaz à infrarouge (pour le CO 2 et H 2 O). Enfin, ils tiennent compte de la conception du système captant les gaz à l'état de traces, des mesures du rapport de mélange ainsi que de l'acquisition des données et de leur réduction afin de mesurer les flux micrométéorologiques. Suit la description des méthodes servant aux instruments nécessaire à la mesure du bilan énergétique par la covariance des fluctuations, tels que...

Methane emissions from a barn and feedlot/paddock housing dairy cattle were estimated using a tracer gas (SF 6 ) to simulate the dispersion of CH 4 . The tracer gas was released from 16 point sources distributed within the barn or feedlot to simulate the CH 4 sources (cows). Using a two-dimensional (y, z) sampling grid, the observed downwind SF 6 /CH 4 crosswind concentration field was integrated to give the portion of the SF 6 /CH 4 plume that was captured by the sampling grid. Assuming that both SF 6 and CH 4 underwent similar turbulent atmospheric transport, the ratio of the respective captured plumes was then used to estimate the emission strength of methane from the known release rate of SF 6 . The predicted source strength of CH 4 from the barn was within 6% of the estimate made using a different technique whereby the entire barn was used as an enclosed chamber. The methane emissions predicted in the barn and feedlot experiments were 542 (( 30%) L CH 4 d -1 cow -1 and 631 (( 30%) L CH 4 d -1 cow -1 , respectively. Using census data on the population of dairy cattle in Canada, a national estimate of 0.245 (( 50%) Tg CH 4 yr -1 was made.

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