Evaluation of nine low-cost-sensor-based particulate matter monitors

Due to their affordability, compact size, and moderate accuracy, low-cost sensors have been studied extensively in recent years. Different manufacturers employ different calibration methodologies and provide users with calibration factors for their models. This study assessed the performance of nine low-cost PM monitors (AirVisual, Alphasense, APT, Awair, Dylos, Foobot, PurpleAir, Wynd, and Xiaomi) in a chamber containing a well-defined aerosol. A GRIMM and a SidePak were used as the reference instruments. The monitors were divided into two groups according to their working principle and data reporting format, and a linear correlation factor for the PM_2.5 mass concentration measurement was calculated for each monitor. Additionally, the differences between the mass concentrations reported by the various monitors and those measured by the reference instruments were plotted against their average before and after user calibration to demonstrate the degree of improvement possible with calibration. Bin-specific calibration was also performed for monitors reporting size distributions to demonstrate coincidence errors that could bias the results. Since monitors designed for residential use often display the air quality index, typically illustrating it with a simplified, color-coded index, the color schemes of various monitors were evaluated against the U.S. EPA regulation to determine whether they could convey the overall air quality accurately and promptly. Although these residential monitors indicated the air quality moderately well, their differing color schemes made the evaluation difficult and potentially inaccurate. Altogether, the tested monitors offer low-cost sensors in packages that are convenient for use and ready for deployment without additional assembly. However, to improve the accuracy of the measurements, user-defined calibration for the target PM source is still recommended.