Laboratory Evaluation of A Personal, Thermophoretic Sampler for Airborne Nanoparticles

Daniel Thayer (1), Kirsten Koehler (1), Amy Prieto (1), Anthony Marchese (1), JOHN VOLCKENS (1)

(1) Colorado State University, Fort Collins

     Abstract Number: 688
     Last modified: May 14, 2010

Abstract
This work describes laboratory tests of a personal, thermophoretic aerosol sampler designed to collect airborne nanoparticles in the breathing zone of exposed individuals. The objective was to make the device small, lightweight, and efficient at collecting airborne nanoparticles over a typical eight-hour workshift. A secondary objective was to challenge the device with a mixture of engineered and incidental nanoparticles and evaluate the ability to discriminate between these two types of particles using energy dispersive analysis in an electron microscope. The sampler measures 5.0 by 3.2 by 7.4 cm (LxWxH), weighs 220 g, and consumes about 7.2 W of power under normal operating conditions. The thermophoretic collection force is applied by a 1100 degree C/cm temperature gradient between two aluminum plates (0.1 cm separation distance) using a resistive heater, a thermoelectric cooler, a temperature controller, and two thermistor sensors. Aerosol was collected onto transmission electron microscopy and scanning electron microscopy substrates for subsequent analysis of particle size, concentration, surface chemistry, and morphology. Particle collection efficiency was determined by challenging the sampler with monodisperse aerosols of 15, 51, 100, and 240 nm at flow rates of 5 and 20 mL/min, respectively. A parallel test system, without the sampler in line, served as a reference control. Particle collection efficiency was near 100% at 5 mL/min and varied from 50-80% at 20 mL/min. Particle diffusion losses inside the device increased with decreasing particle size. Additional tests evaluated the uniformity of particle flux to the collection surface, which varied spatially, but was generally reproducible between tests. These results indicate that thermal precipitation is a feasible approach for efficient collection and analysis of airborne nanoparticles.