JSM 2004 - Toronto

Abstract #301577

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Activity Number: 314
Type: Contributed
Date/Time: Wednesday, August 11, 2004 : 9:00 AM to 10:50 AM
Sponsor: Section on Physical and Engineering Sciences
Abstract - #301577
Title: Fitting Lognormal Distributions to Data from a Size-sorting Particle Device
Author(s): Stanley A. Shulman*+ and Paul A. Baron and Dawn M. Ramsey
Companies: National Institute for Occupational Safety and Health and National Institute for Occupational Safety and Health and National Institute for Occupational Safety and Health
Address: 4676 Columbia Pkwy., MS R-3, Cincinnati, OH, 45226,
Keywords: nonlinear optimization

The cascade impactor is a device for sampling airborne particles to determine the particle mass-weighted aerodynamic-diameter distribution. The particles enter at the top of the device and deposit by decreasing particle diameter on one of the nine stages. Past experimental data has established the fraction of each particle size expected to deposit on each stage. From the nine masses, estimates of the parameters of the lognormal distribution (either a single distribution or a mixture of two) must be obtained. Procedures based on weighted least squares are evaluated for fitting one or two lognormal distributions to both actual and simulated data. For the simulated data, several different scenarios are considered: geometric means and standard deviations producing distinct peaks or indistinct peaks; distributions with substantial mass in the largest particle size stage. A main conclusion is that the weighted least squares solutions produce imprecise estimates of the lognormal parameters.

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