Characterisation Of Particulate Matter Using Microanalysis
Free (open access)
R. J. Odle, P. J. A. Burt & I. J. Slipper
High levels of airborne particulate matter have been implicated in respiratory and cardiovascular diseases, as well as in tumour and blood coagulation/liver function related mortality and morbidity. The exact causative processes are not well understood, but as an aid to epidemiological studies particulate matter of 10 pm and below has been monitored in bulk for some years. The appropriateness of this approach has been questioned, however, as our knowledge of particulate size, morphology and chemistry improves. Compared to those in the sub-micrometre range, larger particles tend to be more complex, containing mixes of agglutinated combustion and abraded mineral products, biological material, salts and metals. The use of cost-effective standard aerobiological methodologies (designed primarily for sampling biological particulates) has been investigated as an aid to improving the collection and rapid analysis of a broad range of particle types. Samples have been viewed in a scanning electron microscope (SEM) with the aim of obtaining morphological and chemical information. Image analysis protocols have been developed to remove background interference caused by the trapping surface and to aid the automatic identification of particles. Non-standard trapping media must be used to provide the necessary stability during sample preparation and in the SEM, due to the stresses caused by high vacuum, temperature and the interaction of the electron beam. The complexity of particle morphology, in particular for agglomerates, has proved to be a challenge and still requires further development work. Results have also highlighted important limitations to the generic applicability of SEM techniques (both in terms of software and hardware) to particulate study. A summary of the results obtained by the different approaches will be presented, and future research requirements summarised.