AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Evaluation of the Alphasense Optical Particle Counter (OPC-N2) and the Grimm Portable Aerosol Spectrometer (PAS-1.108)
SINAN SOUSAN, Kirsten Koehler, Laura Hallett, Thomas Peters, University of Iowa
Abstract Number: 28 Working Group: Instrumentation and Methods
Abstract Although optical particle counters (OPCs) measure in real-time particle number concentration by size, their cost (e.g., >$15,000, PAS-1.108, Grimm Technologies) restricts their widespread use in exposure assessment. We compared the performance of a new, extremely low-cost (~$500) and compact OPC (OPC-N2, Alphasense) to the PAS-1.108. First, we measured detection efficiency by size from 0.5 µm to 5 µm for monodispersed polystyrene latex (PSL) spheres. Then we compared the output of the OPC-N2 to that of the PAS-1.108 and reference instruments for three aerosols (non-absorbing fine particles, nebulized salt solution; absorbing fine particles, welding fume; and coarse dust, aerosolized Arizona road dust) at concentrations up to 12,000 µg/m3. For particles larger than 0.8 µm, the detection efficiency of the OPC-N2 was similar to that of the PAS-1.108, ranging from 66% [1 µm] to 101% [3 µm]. For 0.5-µm particles, the efficiency of the OPC-N2 was 78%, whereas that for the PAS-1.108 was 183%. The number concentration measured with the two OPCs were under or overestimated compared to reference instruments, depending on aerosol type and size. The mass concentration output by the OPCs was highly linear with that measured with the reference instruments (r ≥ 0.97), but the slope and intercept depended strongly on aerosol type suggesting the need to develop a site-specific correction factor. Mass concentration was overestimated with the OPCs for Arizona road dust (OPC-N2, slope = 1.6; PAS, slope = 2.7) and underestimated for welding fume (OPC-N2, slope = 0.05; PAS, slope = 0.4). The coefficient of variation (CV, precision) for OPC-N2 for all experiments was between 4.2% and 16%. These findings suggest that the given site-specific calibrations OPC-N2 can provide similar information to the PAS-1.108 for particles larger than 1 µm.