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FACTORS AFFECTING AEROSOL SAMPLING by Paul A. Baron, Ph.D., NIOSH/DART This chapter adapted from Baron [1]. Contents: 1. 2. 3. 4. 5. 6. 7. 8. 9.
10. 11. 12. 13.
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Inlet Efficiency of the Sampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Classifier Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Cassette Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Electrostatic Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Sample Deposition Uniformity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Sampler Wall Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Collection Media and Analytical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Sampler Field Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 a. Sampler Bias Affected by Internal Deposits . . . . . . . . . . . . . . . . . . . . . . . 194 b. Sampler Precision Affected by Internal Deposits . . . . . . . . . . . . . . . . . . . . 194 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
1. INTRODUCTION The American Conference of Governmental Industrial Hygienists (ACGIH) [2], the International Organization for Standardization (ISO) [3], and the European Standardization Organization (Comité Europeén de Normalisation, CEN) [2,3] have adopted identical particle size-selective sampling conventions for inhalable, thoracic, and respirable aerosols (Figure 1). The purpose of these conventions is to provide a scientific basis for a new generation of particle sizeselective occupational exposure limits (OELs) for aerosols. Such OELs can therefore be matched to the relevant sites of aerosol deposition after inhalation into the respiratory tract, and in turn to the health effects of interest in a given exposure assessment. These sampling conventions are used throughout this manual unless otherwise specified. The criteria presented in this manual are used to determine the most appropriate aerosol sampling equipment. The type of sampling to be performed determines which criteria are important for estimating the adequacy of the sampler and determining aerosol concentration levels. For example, “total dust” samplers generally do not have a size selective particle classifier preceding the filter media and fall under the inhalable sampling convention. Alternatively, sampling for regulatory or voluntary compliance with aerosol exposure standards usually requires greater accuracy, increased efficiency, size-specific selectivity, and good analytical precision. Furthermore, regulations may require the use of a specific sampler and sampling conditions to standardize sampling results (eliminate bias) and reduce uncertainty among laboratory reports. See Chapter P, Measurement Uncertainty and NIOSH Method Accuracy for further discussion on standardization and aerosol measurement error. Over the past two decades, researchers have pointed out strengths and weaknesses with several types of aerosol samplers (Figures 2a-j). Some of these samplers were adapted from
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NIOSH Manual of Analytical Methods
