An automated system for producing uniform surface deposits of dry particles

A laboratory system has been constructed that uniformly deposits dry particles onto any type of test surface. Devised as a quality assurance tool for the purpose of evaluating surface sampling methods for lead, it also may be used to generate test surfaces for any contaminant that uses particles or dust as a transport mechanism. Additionally, it may be used to spike surfaces for studies concerning particle transport, resuspension, reentrainment, and exposure. The electromechanical system includes a rugged aluminum chamber housing deposition equipment, a computer-controlled positioning system, and a 0.61 x 0.61 m target surface area (2 x 2 ft). Media used to evaluate the system have included glass beads of various size fractions (physical diameters between 30 and 500 microm), and Arizona Test Dust (aerodynamic diameters between 1 and 80 microm). Presieved particle size fractions may be used individually to study the effects of monodisperse particles, or may be mixed to create custom polydisperse size distributions. Using arrays of 16 coupons placed on the surface to collect representative samples from every test, the uniformity of the particle deposition can be quantified. The system achieved an average coefficient of variation of less than 20% for the 16 coupons for the particle types and sizes mentioned above and for a variety of total surface loadings (0.3-19 g/m2). Calculations of the system's repeatability (as the average coefficient of variation of mass gains for individual coupon locations compared across multiple identically configured runs) yielded approximately 10 +/- 5% (one standard deviation). Tests of the system's accuracy, defined as the absolute percentage difference between predicted surface loadings and actual loadings, yielded 3.7 +/- 1.3% (one standard deviation).