Characterising single airborne particles by fluorescence emission and spatial analysis of elastic scattered light.

The use of intrinsic fluorescence to characterise airborne particles is often applied to the detection of biological materials, particularly micro-organisms. However, as a number of particles which are found in the atmosphere also fluoresce (whether natural or artificially generated), simple measures of particle fluorescence alone may not be sufficient to indicate the presence of biological agents in the atmosphere. An instrument has been developed for the real-time measurement of aerosols using UV induced fluorescence emission and elastic scattered light to characterise individual particles in terms of size, shape and fluorescence. Particles are detected as they scatter light from a CW red laser beam, which triggers a pulse of 266nm radiation to induce fluorescence. Elastic scatter from the red laser beam is used to measure particle size and shape parameters, and total fluorescence between similar to300 to 500nm is collected. The performance of the instrument has been investigated in laboratory tests and field trials, using a range of biological agent simulants and interferents. An automated classification technique has been applied to assess the ability of the instrument to recognise potential threats against the natural background environment.