A Beta Attenuation System for Mass Determination of Filter-Based Aerosol Samples
JULIAN PROBSDORFER, Emily Macqueene, Jack Kodros, Christian L'Orange, John Volckens, Colorado State University
Abstract Number: 172
Working Group: Instrumentation and Methods
Abstract
Beta attenuation is a reliable, accurate method for aerosol mass monitoring although it is historically limited to large, stationary, high-volume sampling systems. The goal of this work was to develop a laboratory beta-attenuation system for quantifying mass loading on time-integrated filters collected using low-flow (personal) samplers. This system uses a 12mm effective diameter scintillator, a 37MBq C14 source, and is automated with a LabView data-acquisition system. Initial system optimization evaluated the effects of filter size, beam diameter, air gap between the source and detector, temperature, pressure, and relative humidity – all of which had varying degrees of influence on the attenuation measurement. We then developed linear models to correct for this variation. The resultant models, which accounted for mass fluctuations up to 19μg/cm2 were highly linear (R2 = 0.99). Minimizing the air column is most beneficial to improving method detection limit, but a gap is unavoidable due to the need to be able to move filters in and out of the system. By applying our models to a 200-s measurement period, we achieved a lower limit of detection (LLD) of 33μg for a 37mm filter, and 3.5μg LLD for a 12mm filter - equivalent to sampling in a 2.4μg/m3 environment for a 24-hour sample at 1L/min. Additional refinement such as increasing the activity of the C14 source and optimizing the scintillator’s measurement area should allow for further reduction in the LLD and ability to measure smaller filters. With continued development, we expect that this system could out preform gravimetric analysis of miniature air sampling filters resulting in a sub-microgram LLD in the next generation of wearable aerosol sampling devices.