Novel instrumental techniques have been conceived, developed and in one case, patented, which were employed to investigate various aspects of atmospheric dispersion and related topics. The first technique made use of unipolarly ionised air as the tracer 'material', and the results obtained formed the earliest direct experimental evidence of significant concentration fluctuations in vapour/particulate clouds dispersing in the lower atmosphere. Fluctuations are important because they are critical in determining the physiological response associated with exposures to toxic substances and those of importance in malodour nuisance. Later developments in technique included precision control of the unipolar ion current released; these were sufficiently novel to secure a patent. Subsequent innovations involved the development and substantial modification of an existing gas detection method to render its performance fully acceptable for pollution monitoring. This advance led to the invention of the UVIC® detector, described in Volume II, and generated the numerous patent applications referenced therein. Several papers discuss the nature and implications of the information obtained using the experimental methods developed. Examples are the open terrain atmospheric dispersion experiments and analyses, the work on insect pheromones and that on dispersion around an isolated building. From these papers, notably the first, the full impact of concentration fluctuations on the assessment of risks associated with exposure to toxic substances began to emerge. Two papers are included on the investigation of electric field effects arising from factory chimney plumes. Prior to publication, the existence of this phenomenon was not recognised. Papers on the use of electrically charged aerosols for improving deposition efficiency in crop spraying and on the examination of the effects of electrical charging on the behaviour of mildew spores, demonstrate the application of electrical techniques to novel areas of research. It is shown that the method may also have utility for wind tunnel investigations.