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Microsized particles play an important role in many diverse areas of science and technology, for example, surface reactions of micron-sized particles play a key role in astrochemistry, plasma reactors and atmospheric chemistry. To date much of our knowledge of such surface chemistry is derived from 'traditional' surface science-based research. However, the large surface area and morphology of surface material commonly used in such surface science techniques may not necessarily mimic that on the surface of micron/nano scale particles. Hence, a new generation of experiments in which the spectroscopy (e.g., albedo) and chemical reactivity of micron-sized particles can be studied directly must be developed. One, as yet underexploited, non-invasive technique is the use of ultrasonic levitation. In this article, we describe the operation of an 'ultrasonic trap' to store and study the physical and chemical properties of microparticles.

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Synchrotron radiation is a good mimic of solar radiation and therefore has been widely used to study photo-induced physics and chemistry in the terrestrial atmosphere. In this paper we review how synchrotron radiation is being used as a tool for investigating atmospheric physics and chemistry with particular emphasis on studies related to ozone depletion, global warming and ionospheric phenomena. The paper concludes with a discussion of the new possibilities that the next generation of synchrotron-based light sources will provide.