Development of a calibration chamber to evaluate the performance of low-cost particulate matter sensors

Abstract

Low-cost particulate matter (PM) air quality sensors are becoming widely available and are being increasingly deployed in ambient and home/workplace environments due to their low cost, compactness, and ability to provide more highly resolved spatiotemporal PM concentrations. However, the PM data from these sensors are often of questionable quality, and the sensors need to be characterized individually for the environmental conditions under which they will be making measurements. In this study, we designed and assessed a cost-effective (∼$700) calibration chamber capable of continuously providing a uniform PM concentration simultaneously to multiple low-cost PM sensors and robust calibration relationships that are independent of sensor position. The chamber was designed and evaluated with a Computational Fluid Dynamics (CFD) model and a rigorous experimental protocol. We then used this new chamber to calibrate 242 Plantower PMS 3003 sensors from two production lots (Batches I and II) with two aerosol types: ammonium nitrate (for Batches I and II) and alumina oxide (for Batch I). Our CFD models and experiments demonstrated that the chamber is capable of providing uniform PM concentration to 8 PM sensors at once within 6% error and with excellent reliability (intraclass correlation coefficient > 0.771). The study identified two malfunctioning sensors and showed that the remaining sensors had high linear correlations with a DustTrak monitor that was calibrated for each aerosol type (R² > 0.978). Finally, the results revealed statistically significant differences between the responses of Batches I and II sensors to the same aerosol (P-value<0.001) and the Batch I sensors to the two different aerosol types (P-value<0.001). This chamber design and evaluation protocol can provide a useful tool for those interested in systematic laboratory characterization of low-cost PM sensors.

Keywords: Air quality; Calibration chamber; Evaluation of calibration chamber; Low-cost sensors; Particulate matter.

Fig. 1.

Schematic of the calibration system. Note the dimensions are not to scale.

Fig. 2.

Volume fraction distribution at the inlet location, a ±10 mm radial margin from the centerline of the sensors’ inlets. The two smaller concentric circles in the figure represent the inlet of the DustTrack. The larger concentric circle indicates the chamber outlet.

Fig. 3.

Concentration time-series for the ammonium nitrate stability tests.

Fig. 4.

Frequency distribution of slopes, intercepts, coefficients of determination, and bias for 154 Batch I sensors for calibration with ammonium nitrate (A) and alumina oxide (B) aerosols. Note that the scales in the x-axes are different.