Site characterization, small-scale

For a small-scale retrospective study, participants enter and study a field in which a pesticide has been used over a period of time. The purposes of small-scale retrospective studies are to determine whether the pesticide(s) in question has leached to ground water in certain fields, and to characterize the leaching pattern in the soil profile at a given point in time. This section contains discussions on site selection, site characterization, the number and location of observation wells, well construction and sampling, and soil sampling. 

In Copenhagen, another major city of the whole network, street sites (sites 3b and 3c) were also characterized by significantly higher trace element concentrations in grass cultures than most other sites in the municipal area (Fig. Ic, d). Urban sites such as sites 1 and 4 also showed somewhat higher elements levels than suburban and reference locations. On the example of sites 3b and 3c in Copenhagen, also the small-scale spatial differentiation of biomonitoring results can be demonstrated. Both these sites were installed at a major square in the city... 

To understand heterogeneous catalysis it is necessary to characterize the surface of the catalyst, where reactants bond and chemical transformations subsequently take place. The activity of a solid catalyst scales directly with the number of exposed active sites on the surface, and the activity is optimized by dispersing the active material as nanometer-sized particles onto highly porous supports with surface areas often in excess of 500m /g. When the dimensions of the catalytic material become sufficiently small, the properties become size-dependent, and it is often insufficient to model a catalytically active material from its macroscopic properties. The structural complexity of the materials, combined with the high temperatures and pressures of catalysis, may limit the possibilities for detailed structural characterization of real catalysts. 

High Resolution Electron Energy Loss Spectroscopy has been "discovered" at about the same time as the previous cited techniques - die first reported experiment is related to a study of small molecules adsorbed on a (100)W surface and is dated from 1967 (1). During the last 15 years, the characterization of adsorption states of molecules on metal and semiconductor surfaces was the principal attribute of HREELS information on the elemental composition, on the chemistry, and the kinetics of surface reactions (versus temperature and/or time) were studied. One significant "plus" of HREELS is its ability to identify adsorption sites on a metal, by using the "dipole-selection rule" it is therefore possible to gain information on the short-scale structure or morphology of a surface with HREELS. 

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