Investigating Measurement Variation of Modified Low-Cost Particle Sensors

Particulate matter (PM) has demonstrably increased rates of cardiovascular and respiratory related disease; thus, a low-cost sensor that accurately measures PM is desirable including for smaller and more private environments such as residential homes. The low-cost Dylos and the Utah Modified Dylos Sensor (UMDS) have been shown to be highly correlated with references instruments for measuring particle counts and aerosol concentrations, which makes them useful tools for air quality studies. An analytical calibration equation (calibration) is used to describe the linear relationship between the UMDS and a reference instrument, providing the best estimate of PM concentrations when the UMDS is operated. In this study, an investigation of measurement variation of a UMDS was performed using a low-cost calibration technique to determine differences between the brand new UMDS pre-calibration equation (Prec), a contaminated UMDS post-calibration equation (Postc), and a cleaned UMDS clean calibration equation (CC). The UMDS were calibrated against a high-grade aerosol spectrometer (Grimm model 1.109) as a reference instrument. Calibrations took place in a home or office environment. Counts per volume units from the UMDS were matched to the Grimm's for comparison. The investigation of the UMDS for measurement variation was performed for the approximate estimates of PM2.5 by using the small bin (i.e. ≥0.50μm) subtracted from the large bin (i.e. ≥2.5μm), and for total particulates by using the large bin. Linear regressions were performed between the UMDS and the Grimm per calibration event, which produced R2 values and slopes that were indicative of measurement variation. Data exceeding the upper limit of quantification (ULOQ) of 106,000 particles/liter and the lower limit of quantification (LLOQ) of 4 particles/liter were excluded from statistical comparison. R2 values greater or equal to 0.70 were used to assess measurement variation as a quality control standard for valid comparisons. A rank sum statistical test between calibration comparisons was performed. Prec/Postc and Prec/CC had significant differences indicating measurement variation. Postc/CC did not have any significant differences; cleaning the UMDS had no effect and did not demonstrate measurement variation. Reasons for measurement variation may include instrument contamination (dust/dirt), hardware degradation, altered fan flow rates, and potentially inadequate cleaning of the UMDS. Future work may investigate the rate of measurement variation in order to develop a recommended re-calibration schedule in order to maintain the most accurate estimates of PM for UMDS in long-term operation.

Characterization of CO and NO2 exposures of ice skating rink maintenance workers

Air quality is a common concern among indoor ice rink facilities due to the use of gasoline/propane ice resurfacing equipment. Although previous studies have investigated spectator, guest, and skater exposures, a review of the literature revealed little published research regarding ice maintenance employees' exposures. Ice maintenance includes edging and resurfacing. The resurfacer is commonly referred to as a Zamboni®. Edging is almost always followed by resurfacing, but resurfacing frequently happens independently of edging. The purpose of this study was to characterize ice rink maintenance employees' exposures to CO and NO₂. Employees from four ice rinks in Salt Lake County, Utah were sampled using direct reading instruments during routine ice maintenance activities. Maintenance was divided into four activities: 1) Edging only, 2) Resurfacing after edging (not including edging), 3) Edging and resurfacing (Activities 1 and 2 combined), and 4) Resurfacing only (independent of edging). Activities 1, 2 and 3 were sampled twenty-four (n = 24) times. Activity 4 was sampled eight times. Sampling results were graphed and summarized using descriptive statistics. The highest measured CO concentration was 202 ppm, which occurred during edging. Average CO concentrations for all activities ranged from 0 ppm to 60.4 ppm. Minimal CO exposure was observed when resurfacing occurred without edging, which implies that elevated CO exposure measured while using the resurfacer may be residual CO from prior edging activities. NO₂ concentrations were negligible for all rinks and all activities. Results confirmed that gasoline edgers significantly contribute to indoor CO levels, with peak levels exceeding some recommended exposure levels. Indoor ice rink facilities should monitor employees' CO exposures and implement procedures to limit exposures. This may be achieved by limiting the number of laps taken with the edger or replacing gasoline powered edgers with electric edgers.

Performance of prototype high-flow inhalable dust sampler in a livestock production facility

A high-flow inhalable sampler, designed for operational flow rates up to 10 L/min using computer simulations and examined in wind tunnel experiments, was evaluated in the field. This prototype sampler was deployed in collocation with an IOM (the benchmark standard sampler) in a swine farrowing building to examine the sampling performance for assessing concentrations of inhalable particulate mass and endotoxin. Paired samplers were deployed for 24 hr on 19 days over a 3-month period. On each sampling day, the paired samplers were deployed at three fixed locations and data were analyzed to identify agreement and to examine systematic biases between concentrations measured by these samplers. Thirty-six paired gravimetric samples were analyzed; insignificant, unsubstantial differences between concentrations were identified between the two samplers (p = 0.16; mean difference 0.03 mg/m³). Forty-four paired samples were available for endotoxin analysis, and a significant (p = 0.001) difference in endotoxin concentration was identified: the prototype sampler, on average, had 120 EU/m³ more endotoxin than did the IOM samples. Since the same gravimetric samples were analyzed for endotoxin content, the endotoxin difference is likely attributable to differences in endotoxin extraction. The prototype's disposable thin-film polycarbonate capsule was included with the filter in the 1-hr extraction procedure while the internal plastic cassette of the IOM required a rinse procedure that is susceptible to dust losses. Endotoxin concentrations measured with standard plastic IOM inserts that follow this rinsing procedure may underestimate the true endotoxin exposure concentrations. The maximum concentrations in the study (1.55 mg/m³ gravimetric, 2328 EU/m³ endotoxin) were lower than other agricultural or industrial environments. Future work should explore the performance of the prototype sampler in dustier environments, where concentrations approach particulates not otherwise specified (PNOS) limits of 10 mg/m³, including using the prototype as a personal sampler.

Ambient and laboratory evaluation of a low-cost particulate matter sensor

Low-cost, light-scattering-based particulate matter (PM) sensors are becoming more widely available and are being increasingly deployed in ambient and indoor environments because of their low cost and ability to provide high spatial and temporal resolution PM information. Researchers have begun to evaluate some of these sensors under laboratory and environmental conditions. In this study, a low-cost, particulate matter sensor (Plantower PMS 1003/3003) used by a community air-quality network is evaluated in a controlled wind-tunnel environment and in the ambient environment during several winter-time, cold-pool events that are associated with high ambient levels of PM. In the wind-tunnel, the PMS sensor performance is compared to two research-grade, light-scattering instruments, and in the ambient tests, the sensor performance is compared to two federal equivalent (one tapered element oscillating microbalance and one beta attenuation monitor) and gravimetric federal reference methods (FEMs/FRMs) as well as one research-grade instrument (GRIMM). The PMS sensor response correlates well with research-grade instruments in the wind-tunnel tests, and its response is linear over the concentration range tested (200-850 μg/m3). In the ambient tests, this PM sensor correlates better with gravimetric methods than previous studies with correlation coefficients of 0.88. However additional measurements under a variety of ambient conditions are needed. Although the PMS sensor correlated as well as the research-grade instrument to the FRM/FEMs in ambient conditions, its response varies with particle properties to a much greater degree than the research-grade instrument. In addition, the PMS sensors overestimate ambient PM concentrations and begin to exhibit a non-linear response when PM2.5 concentrations exceed 40 μg/m3. These results have important implications for communicating results from low-cost sensor networks, and they highlight the importance of using an appropriate correction factor for the target environmental conditions if the user wants to compare the results to FEM/FRMs.

Sampling efficiency of modified 37-mm sampling cassettes using computational fluid dynamics

In the U.S., most industrial hygiene practitioners continue to rely on the closed-face cassette (CFC) to assess worker exposures to hazardous dusts, primarily because ease of use, cost, and familiarity. However, mass concentrations measured with this classic sampler underestimate exposures to larger particles throughout the inhalable particulate mass (IPM) size range (up to aerodynamic diameters of 100 μm). To investigate whether the current 37-mm inlet cap can be redesigned to better meet the IPM sampling criterion, computational fluid dynamics (CFD) models were developed, and particle sampling efficiencies associated with various modifications to the CFC inlet cap were determined. Simulations of fluid flow (standard k-epsilon turbulent model) and particle transport (laminar trajectories, 1-116 μm) were conducted using sampling flow rates of 10 L min(-1) in slow moving air (0.2 m s(-1)) in the facing-the-wind orientation. Combinations of seven inlet shapes and three inlet diameters were evaluated as candidates to replace the current 37-mm inlet cap. For a given inlet geometry, differences in sampler efficiency between inlet diameters averaged less than 1% for particles through 100 μm, but the largest opening was found to increase the efficiency for the 116 μm particles by 14% for the flat inlet cap. A substantial reduction in sampler efficiency was identified for sampler inlets with side walls extending beyond the dimension of the external lip of the current 37-mm CFC. The inlet cap based on the 37-mm CFC dimensions with an expanded 15-mm entry provided the best agreement with facing-the-wind human aspiration efficiency. The sampler efficiency was increased with a flat entry or with a thin central lip adjacent to the new enlarged entry. This work provides a substantial body of sampling efficiency estimates as a function of particle size and inlet geometry for personal aerosol samplers.

A Simple and Disposable Sampler for Inhalable Aerosol

The state-of-the-art for personal sampling for inhalable aerosol hazards is constrained by issues of sampler cost and complexity; these issues have limited the adoption and use of some samplers by practicing hygienists. Thus, despite the known health effects of inhalable aerosol hazards, personal exposures are routinely assessed for only a small fraction of the at-risk workforce. To address the limitations of current technologies for inhalable aerosol sampling, a disposable inhalable aerosol sampler was developed and evaluated in the laboratory. The new sampler is designed to be less expensive and simpler to use than existing technologies. The sampler incorporates a lightweight internal capsule fused to the sampling filter. This capsule-filter assembly allows for the inclusion of particles deposited on the internal walls and inlet, thus minimizing the need to wash or wipe the interior sampling cassette when conducting gravimetric analyses. Sampling efficiency and wall losses were tested in a low-velocity wind tunnel with particles ranging from 9.5 to 89.5 μm. The results were compared to the proposed low-velocity inhalability criterion as well as published data on the IOM sampler. Filter weight stability and time-to-equilibrium were evaluated as these factors affect the practicality of a design. Preliminary testing of the new sampler showed good agreement with both the IOM and the proposed low-velocity inhalability curve. The capsule and filter assemblies reached equilibrium within 25h of manufacturing when conditioned at elevated temperatures. After reaching equilibrium, the capsule-filter assemblies were stable within 0.01mg.

Evaluation of respirable crystalline silica in high school ceramics classrooms

Air concentrations of respirable crystalline silica were measured in eleven (11) high school ceramics classrooms located in Salt Lake County, UT, USA. Respirable dust was collected on PVC filters using precision flow pumps and cyclone samplers (n = 44). Filters were subsequently analyzed for respirable dust and percent crystalline silica content. The geometric mean of the silica concentrations was 0.009 mg/m³ near the teacher’s work station and 0.008 mg/m³ near the kilns. The number of students in the classroom was correlated to the silica concentration in the ceramics classroom, but no correlation was found between the silica concentrations and either the size of the classroom or the age of the building. Results from this study indicate that ceramics teachers may be at an increased risk of exposure to crystalline silica based on the ACGIH TLV of 0.025 mg/m³, with an exceedance of 21%.