Sampling and Measurement for Respirable Particulates

Respirable Particulates Introduction Aerosol particle concentration is measured by means of aerosol sampler Two types of sampling: –Continuous sampling- provides a more statistically consistent result –Batch wise sampling

Respirable Particulates Continuous Sampling Air is drawn through a particulate sampler Types of particulate sampler: –Filters –Impactors –Direct reading samplers Flow rate in most cases is less than 2 lit/min

Respirable Particulates Filters Filters are used when sampling for total suspended particles Air sample is aspirated through one or more openings in the solid casing of the filter holder The particles are collected on the filter which is subsequently examined

Respirable Particulates Filters Factors affecting selection of filter –Collection efficiency –Pressure Drop –Background contamination –Compatibility with analytical methods Filters suitable for indoor particles –Cellulose –Fiber –Membrane

Respirable Particulates Cascade Impactors Used to determine total suspended particles and particle size distribution A multi stage impaction device used to separate airborne particles into size classes on the basis of their aerodynamic diameter Aerosol is drawn through a series of progressively narrower jets each of which is followed by an impaction surface

Respirable Particulates Calibration of test instruments Two types of test aerosols are generally used: –Monodispersed aerosols – Used to calibrate particle size measuring instruments and to determine the effect of particle size on sampling devices –Polydispersed aerosols- Used in the laboratory to simulate the conditions under which sampler would be used. Dioctyl phthalate (DOP) is frequently used in testing high efficiency particulate aerosol filters and for calibrating instruments

Respirable Particulates Sampling for ETS No satisfactory technique to measure the particulate matter and chemicals produced from ETS Method currently used to collect main stream (MS) smoke duplicates the process of puffing a cigarette –Burning end of a cigarette is held under conditions comparable to that of a cigarette being smoked Most frequently used instrument to generate Side Stream (SS) smoke is the modified Neurath chamber

Respirable Particulates Types of Samplers Traditionally fixed stations (area sampler) has been used Personal air samplers have been introduced lately Direct reading particle samplers currently in use are : –Electric aerosol analyzers –Optical particle counters –Integrating nephelometer