Measurement of Airborne Particles

Abstract only: This chapter examines instrumental methods for the determination of particle physical properties. The main properties which are considered include particle mass and number concentrations, number and mass size distribution, and to a lesser extent, particle surface area. Some of the methods discussed require sample collection on a medium, for further analyses and determination of the property under investigation. An example of this is the collection of particles on a filter, from the sampled airflow, for further gravimetric determination of particle mass or chemical composition. In cases like this only the mechanisms and instrumentation for capturing the particles are discussed, not the further analytical methods for microscopic, gravimetric, chemical or biological analyses. Methods for chemical and biological characterization of particles are discussed in more detail in chapters 3.1 and 2.4. Many of the methods available for characterization of particle physical properties yield real-time data and do not require capture of the analyzed particles. Such methods are particularly desirable for indoor investigations as they usually enable shorter measurement times and provide information relating to time variation of the properties investigated. However, a shortcoming of some of these methods is that they do not directly measure the property of interest, but recalculate its value based on another measured property. For example, an optical instrument does not measure particle mass, and if the reading of the instrument indicates mg m-3, without previous calibration of the instrument for the specific measured aerosol, the quantity measured must be regarded as a very crude approximation. To ensure the proper application of instruments and to avoid misinterpretation of the results it is thus important to understand the principles of operation of the instruments used for particle characterization; their advantages and shortcomings for specific applications; as well as the properties which are measured directly and those which are determined indirectly, . This chapter briefly discusses principles of operation of the most common methods for characterization of particle physical properties and provides an overview of measurement devices and methods and their features, for indoor measurements.