Typical field study scenario

The third need is standardization. The receptor model applications need to be written as standard computer routines, common data structures that can accomodate uncertainties of the observables need to be created, and sampling and analysis equipment and procedures must produce equivalent results. Field study "scenarios" for typical situations should be proposed. 

Future development efforts in field study design and data management should 1) develop methodologies for choosing sampler location, sampling schedule, and sampling devices 2) measure the collection efficiency of available samplers as a function of particle size, windspeed and wind direction 3) create a series of "typical" design scenarios which can be specified for different aerosol study objectives 4) develop standardized data bases from which ambient and source information can be recovered. 

Although the influence of relevant biotic and abiotic variables on the fate and effects of chemicals can, to a certain extent, be explored through controlled experiments and observations of natural systems, the combinations of factors that can be tested in practice are very limited. Mesocosm and field studies are often expensive to perform, can be difficult to replicate sufficiently, and are frequently complicated to interpret. Because they typically represent one unique scenario (species composition and density, temperature, light, nutrient level, and timing of pesticide application in relation to the environmental conditions), questions are often raised about the generality and robustness of the results. Likewise, unexpected or uncontrollable events may occur (e.g., it may have been an unusually rainy, sunny, hot, or cool season), the influence of which on the estimate of risk can be difficult to assess. 

While the importance of the breakdown of the BOA in thermal chemistry is still controversial, the time-reversed process of creating chemistry from hot electrons is well established. Because experiments are generally performed under conditions where there is no adiabatic chemistry, hot electron induced chemistry is easily identified and studied, even when the cross-section for the chemistry is very small. Typical scenarios involve photochemistry, femtochemistry and single molecule chemistry on surfaces. A few well-studied examples are discussed briefly in Section 4.8. Because a detailed discussion of these active fields would take this chapter far from its original purpose, they are only treated briefly to illustrate the relationship to other aspects of bond making/breaking at surfaces. 

Matching dose to anticipated field exposnres is difficnlt as, even when the area dose levels are expected to bracket anticipated exposnre levels, the nature of the exposure is different. In the experimental study, the full dose of the compound is applied at the beginning of the exposure period, whereas in the typical exposure scenario, the dose is received incrementally over the course of, for instance, the... 

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