| Summary: | 博士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 88 === The ultimate goal of aerosol sampling is to evaluate the health hazard caused by the deposited particles in the human breathing system. The ideal sampler that can provide the accurate monitoring of the ambient aerosol is also used to estimate the contribution of the human health effects. Therefore, aerosol must enter the sampler and be deposited on the collection medium without loss. Currently conducting with a 25-mm diameter filter cassette, and a 50-mm long straight tubular inlet to sample for asbestos and other fibers requires that the sample be uniformly deposited on the filter. The asbestos fiber analytical methods require such uniform deposition because only small, randomly chosen locations on the filter are observed in the analysis. However, non-uniform fiber deposition can directly reduce the accuracy and precision of the fiber measurement method.
The latest performance standards, set by the American Conference of Governmental Industrial Hygienists (ACGIH), International Standards Organization (ISO), and Comite European de Normalisation (CEN), clearly define the aerosol size-selective characteristics of respirable convention (alveolar or gas exchange region), thoracic convention (tracheo-bronchial region), and inhalable convention (head-airways region). These penetration curves have been modeled. Application of the respirable criterion or the thoracic criterion to fiber sampling would restrict the measurement of fibers to those most likely to pose a hazard. For now, size-selective sampling has not been officially applied to fiber method, so one of the major objectives of this work is to develop a respirable sampler for fibrous aerosol particles. This size-selective device is expected to deliver an aerosol deposition with satisfactory uniformity.
An ultrasonic atomizing nozzle was used to generate challenge aerosol particles (methylene blue). A 25-mCi radioactive source, Po210, was used to neutralize the methylene blue particles to the Boltzmann charge equilibrium. An Aerodynamic Particle Sizer was used to measure the number concentrations and size distributions upstream and downstream of the size-selective devices. Both the precision and accuracy of the samplers to be tested was analyzed and revealed as a function of particle size. In addition to the fit to the internationally-defined convention, the filter deposit, after exposed to the water vapor, was examined visually or analyzed by using a MATLAB program for uniformity. All the currently commercially available aerosol samplers and the devices developed in this study were evaluated for not only the fit to the international standards but also whether the device(s) delivered a uniform distribution across the filter. The fiber measurement method was compared with the regular PCM (Phase Contrast Microscope) procedure.
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