Presented by: Jen Brown, Met One Instruments, Inc. 

Summary: This experimental study compares regulatory PM1.0, PM2.5, and PM10 mass concentration measurements with results from real-time optical particle counter (OPC) mass measurement devices.  Total mass in the form of PM1.0, PM2.5, and PM10 was continuously measured during the event using US-EPA FEM designated beta attenuation mass monitors “BAM”.  Three “BAM” units were collocated with three OPC  mass measurement devices at each of three different locations:  Elizabeth NJ, Salt Lake City UT, and Riverside CA.  Data comparisons include hourly and 24-hour averages.  Analysis of data from May 2019-June 2020 reveal excellent PM10 linear correlation coefficients of 0.79, 0.90, and 0.91; PM2.5 linear correlation coefficients of 0.65, 0.77, and 0.75; and PM1.0 linear correlation coefficients of 0.51, 0.72, and 0.64 for each respective site (NJ, UT, CA).  OPC versus “BAM” slopes differ between mass size concentrations at each site, as well as when comparing the same mass size cut point between different sites.  This provides evidence of the importance of a k factor to accommodate for dissimilar ambient conditions at different sites.  Flow is critical to the accuracy of optical particle counters; flow stability is vital to minimize drift.  The OPC mass measurement units maintained excellent intra-model precision across the study, and this is attributed to its enhanced internal flow system.  Meteorological parameters have been investigated to explain occasional large shifts from FEM reported particulate concentration measurements.

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