Evaluation of PM2.5 measured in an urban setting using a low-cost optical particle counter and a Federal Equivalent Method Beta Attenuation Monitor

We present the results of a multi-season field evaluation of a low-cost optical particle counting sensor (Purple Air PA-II) that reports mass concentration of particulate matter with diameter less than 2.5 microns (PM2.5), and is part of a relatively large and growing network of microelectronic internet-of-things sensors. We assessed 16 months of PA-II PM2.5 data collected in a near-road urban setting in the humid climate of Charlotte, North Carolina. The PA-II was collocated with a Federal Equivalent Method Beta Attenuation Monitor (BAM model 1022), and with a weather station that monitored ambient relative humidity (RH) and temperature (T). We tested and used a multiple linear regression model with BAM PM2.5, RH, and T as predictors to model the reported PA-II PM2.5. The results show a 27-57% improvement in the accuracy of the PA-II PM2.5 data relative to the reference data from the BAM, with the highest percentage improvements for moderate to high RH. The methodologies in our study are broadly applicable to other field studies of low-cost monitors, and the results are a critical improvement that suggest that PA-II may indeed be suitable for air quality, health, and urban aerosol research. Copyright (c) 2019 American Association for Aerosol Research