Evaluation of the Alphasense optical particle counter (OPC-N2) and the Grimm portable aerosol spectrometer (PAS-1.108)

We compared the performance of a low-cost (∼500), compact optical particle counter (OPC, OPC-N2, Alphasense) to another OPC (PAS-1. 108, Grimm Technologies) and reference instruments. We measured the detection efficiency of the OPCs by size from 0. 5 to 5 μm for monodispersed, polystyrene latex (PSL) spheres. We then compared number and mass concentrations measured with the OPCs to those measured with reference instruments for three aerosols: salt, welding fume and Arizona road dust. The OPC-N2 detection efficiency for monodispersed was similar to the PAS-1. 108 for particles larger than 0. 8 μm (minimum of 79% at 1 μm and maximum of 101% at 3 μm). For 0. 5-μm particles, the detection efficiency of OPCN2 was underestimated at 78%, whereas PAS-1. 108 overestimated concentrations by 183%. The mass concentrations from the OPCs were linear (r ≥ 0. 97) with those from the reference instruments for all aerosols, although the slope and intercept were different. The mass concentrations were overestimated for dust (OPC-N2, slope = 1. 6; PAS-1. 108, slope = 2. 7) and underestimated for welding fume (OPC-N2, slope = 0. 05; PAS-1. 108, 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, given site-specific calibrations, the OPC-N2 can provide number and mass concentrations similar to the PAS-1. 108 for particles larger than 1 μm.