Chapter 13 - Experimental design

Summary

How odd it is that anyone should not see that any observation must be for or against some view if it is to be of any service.

Charles Darwin (1861) in a letter to Henry Fawcett, quoted by S. J. Gould in Dinosaur in a Haystack.

Concepts

Many factors can contribute to theway in which observational programmes to measure concentrations of trace gases are established. These include factors such as

1. ▪ perceptions of scientific need,

2. ▪ recognition of the potential of new measurement technology,

3. ▪ availability of researchers with specific skills; and

4. ▪ funding.

Apart from the choices of which gases are measured and by what technique, an important question is the locations at which air is sampled or measurements are made. Often initial sampling, particularly in a development phase, is based on opportunity. Samples are collected, or measurements made, as close as possible to the home base of the researchers involved. Beyond this, ad hoc criteria are often used: remote sites may have good signal-to-noise ratios, but may undersample important regions.

In view of the considerable cost and effort required to establish measurement programmes, it is desirable to assess the likely utility of such programmes in advance. As well as the question of where to sample, there are issues such as the extent to which new measurements might duplicate existing measurements. Particular cases are the relative role of isotopes and other multi-tracer studies.

This chapter concerns the use of modelling of atmospheric transport in this type of ‘experimental-design’ mode.