Evaluations of Three Low-Cost PM Monitors Against a Reference PM Instrument

In recent years, low-cost particulate matter (PM) monitors have significantly drawn scientific attention for their affordable cost and feasibility. These low-cost monitors are used to measure PM number and mass concentrations in various size ranges and compositions. One of the main objectives of the current study was to evaluate the accuracy of three different low-cost monitors (PupleAir, Dylos, Speck) against a reference instrument (Scanning Mobility Particle Sizer (SMPS)) in the presence of particles from grilling beef and candle burning under controlled laboratory conditions. We also evaluated the performance of the Purple Air monitor against the gravimetric mass measurement and a research level instrument, AQS1 (Aeroqual, New Zealand) in an on-campus residential apartment during several indoor activities including cooking, dishwashing, microwaving, vacuum cleaning, etc. The PurpleAir which showed good performance in the laboratory stage of the project for both candle burning and grilling beef. The correlation coefficients against SMPS were found to be 0.7 and 0.6 for grilling and candle burning, respectively. Also in the residential apartment, the average mass concentrations over 36 hours of continuous operation of Purple Air were 9.7, 14.1, and 15.0 µg/m³ for PM₁, PM_2.5, and PM_10, respectively, while the PM₁, PM_2.5, and PM₁₀ concentrations using the reference gravimetric measurements were 12.7, 20.8, 47.7 µg/m³, respectively. The performance of the Purple Air was better than the AQS1 compared to the reference method in terms of the average mass concentration over 32 hours of the continuous operation. However, when a source like cooking was performed in the apartment, the Purple Air showed the peak concentration with a delay and significantly less than the research level instrument (AQS1). Time and concentration averaging as well as the method of the experiments (locating the monitors near the source or away from the source) can significantly impact the accuracy of the monitors.