Exploring Evaluation Variables for Low-Cost Particulate Matter Monitors to Assess Occupational Exposure

Abstract

(1) Background: Small, lightweight, low-cost optical particulate matter (PM) monitors are becoming popular in the field of occupational exposure monitoring, because these devices allow for real-time static measurements to be collected at multiple locations throughout a work site as well as being used as wearables providing personal exposure estimates. Prior to deployment, devices should be evaluated to optimize and quantify measurement accuracy. However, this can turn out to be difficult, as no standardized methods are yet available and different deployments may require different evaluation procedures. To gain insight in the relevance of different variables that may affect the monitor readings, six PM monitors were selected based on current availability and evaluated in the laboratory; (2) Methods: Existing strategies that were judged appropriate for the evaluation of PM monitors were reviewed and seven evaluation variables were selected, namely the type of dust, within- and between-device variations, nature of the power supply, temperature, relative humidity, and exposure pattern (peak and constant). Each variable was tested and analyzed individually and, if found to affect the readings significantly, included in a final correction model specific to each monitor. Finally, the accuracy for each monitor after correction was calculated; (3) Results: The reference materials and exposure patterns were found to be main factors needing correction for most monitors. One PM monitor was found to be sufficiently accurate at concentrations up to 2000 µg/m3 PM2.5, with other monitors appropriate at lower concentrations. The average accuracy increased by up to three-fold compared to when the correction model did not include evaluation variables; (4) Conclusions: Laboratory evaluation and readings correction can greatly increase the accuracy of PM monitors and set boundaries for appropriate use. However, this requires identifying the relevant evaluation variables, which are heavily reliant on how the monitors are used in the workplace. This, together with the lack of current consensus on standardized procedures, shows the need for harmonized PM monitor evaluation methods for occupational exposure monitoring.

Features and Practicability of the Next-Generation Sensors and Monitors for Exposure Assessment to Airborne Pollutants: A Systematic Review

“…To date, the use of NGMSs in occupational hygiene applications is less frequent, mainly because policy- and legislation-based decisions have the strictest performance requirements for precision, accuracy, completeness, and detection limit of data [ 95 ]. Nevertheless, NGMSs sensing devices can offer new opportunities in the field of occupational safety and health management [ 4 , 22 , 41 , 45 , 61 , 62 , 92 , 96 , 97 , 98 , 99 ]. Some of the most interesting applications of NGMSs are reported hereafter.…”

“…Furthermore, NGMSs can report and process the data as soon as they are collected and while the instrument is still deployed (i.e., real-time analysis). Therefore, due to their features (i.e., reduced cost, ease of deployment, direct reading capabilities together with the wireless network ability and the possibility of integrating them with other exposure estimation methods), new ways of collecting and sharing environmental and occupational exposure information has become possible using NGMSs [ 4 , 22 ]. For these reasons, both in environmental and occupational hygiene, not only is the need for accurate evaluation of human exposure to airborne pollutants confirmed and reiterated, but a step forward is required as regards the methods, techniques, and technologies to be used for this purpose.…”

“…Moreover, biases in the acquisition and interpretation of the data obtained with NGMSs can be derived from different sources of measurement error and interference, which arise once operating in the field and which cannot be completely covered in the development and calibration phases carried out in the laboratory [ 101 ]. For these reasons, NGSMs should be operated applying rigorous quality assurance and quality control protocols [ 4 , 49 ]. Focusing on the concept mentioned above, Fishbain et al [ 107 ] proposed a sensor evaluation toolbox (SET) for evaluating air quality micro sensing units, based on different performance measures and environments.…”

“…In any case, MMs are those devices having significantly lower dimensions than reference-grade instrumentation. Among MMs, a particular category of sensors and monitors are wearable monitors (WMs), i.e., small, lightweight monitors being used as wearables to provide real-time personal exposure measurements [ 3 , 4 ]. There is still a lack of a universally agreed upon definition of low-cost monitors (LCMs) [ 5 ].…”

“…There is still a lack of a universally agreed upon definition of low-cost monitors (LCMs) [ 5 ]. Although some different definitions are available [ 6 , 7 ], the scientific community generally defines them as those having significantly lower costs than reference-grade instrumentation [ 4 ], in such a way that the acquisition of a single unit has a minimal impact on the budget for monitoring activities. For the purpose of this study, an LCM is defined as a monitor, the cost of which does not exceed the order of magnitude of a few hundreds of dollars [ 7 , 8 ].…”