Abstract
Deployment of low-cost sensors in the field is increasingly popular. However, each sensor requires on-site calibration to increase the accuracy of the measurements. We established a laboratory method, the Average Slope Method, to select sensors with similar response so that a single, on-site calibration for one sensor can be used for all other sensors. The laboratory method was performed with aerosolized salt. Based on linear regression, we calculated slopes for 100 particulate matter (PM) sensors, and 50% of the PM sensors fell within ±14% of the average slope. We then compared our Average Slope Method with an Individual Slope Method and concluded that our first method balanced convenience and precision for our application. Laboratory selection was tested in the field, where we deployed 40 PM sensors inside a heavy-manufacturing site at spatially optimal locations and performed a field calibration to calculate a slope for three PM sensors with a reference instrument at one location. The average slope was applied to all PM sensors for mass concentration calculations. The calculated percent differences in the field were similar to the laboratory results. Therefore, we established a method that reduces the time and cost associated with calibration of low-cost sensors in the field.
Highlights
The Occupational Safety and Health Administration (OSHA) requires that a worker’s exposure to respirable particulate matter (PM), those particles that can penetrate to the alveolar regions of the lungs [1], is less than 5 mg/m3 in an 8-h, time-weighted, average concentration
We evaluated the limit of detection (LOD) for our lowest concentration generated inside the chamber based on Zikova, et al [29] method
We found that the sensor responses were similar in the three experiments, where the coefficient of variation was less than 10%
Summary
The Occupational Safety and Health Administration (OSHA) requires that a worker’s exposure to respirable particulate matter (PM), those particles that can penetrate to the alveolar regions of the lungs [1], is less than 5 mg/m3 in an 8-h, time-weighted, average concentration. Respirable particulate matter is measured with a gravimetric filter or federal equivalent methods [2,3]. High-accuracy, gravimetric methods are expensive and only provide time-weighted average measurements [4]. Increasing the number of filter measurements spatially and temporally allows exploration of exposure variability to establish appropriate control methods. The regulatory framework discourages additional sampling due to the increasing probability of measuring an exceedance of the occupational exposure limits [5]
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