Improving the UNC Passive Aerosol Sampler Model Based on Comparison with Commonly Used Aerosol Sampling Methods

Abstract

ObjectivesIn an occupational environment, passive sampling could be an alternative to active sampling with pumps for sampling of dust. One passive sampler is the University of North Carolina passive aerosol sampler (UNC sampler). It is often analysed by microscopic imaging. Promising results have been shown for particles above 2.5 µm, but indicate large underestimations for PM2.5. The aim of this study was to evaluate, and possibly improve, the UNC sampler for stationary sampling in a working environment.MethodsSampling was carried out at 8-h intervals during 24 h in four locations in an open pit mine with UNC samplers, respirable cyclones, PM10 and PM2.5 impactors, and an aerodynamic particle sizer (APS). The wind was minimal. For quantification, two modifications of the UNC sampler analysis model, UNC sampler with hybrid model and UNC sampler with area factor, were compared with the original one, UNC sampler with mesh factor derived from wind tunnel experiments. The effect of increased resolution for the microscopic imaging was examined.ResultsUse of the area factor and a higher resolution eliminated the underestimation for PM10 and PM2.5. The model with area factor had the overall lowest deviation versus the impactor and the cyclone. The intraclass correlation (ICC) showed that the UNC sampler had a higher precision and better ability to distinguish between different exposure levels compared to the cyclone (ICC: 0.51 versus 0.24), but lower precision compared to the impactor (PM10: 0.79 versus 0.99; PM2.5: 0.30 versus 0.45). The particle size distributions as calculated from the different UNC sampler analysis models were visually compared with the distributions determined by APS. The distributions were obviously different when the UNC sampler with mesh factor was used but came to a reasonable agreement when the area factor was used.ConclusionsHigh resolution combined with a factor based on area only, results in no underestimation of small particles compared to impactors and cyclones and a better agreement with the APS’s particle size distributions. The UNC sampler had lower precision than the impactors, but higher than the respirable cyclone. The UNC sampler with area factor could be used for PM2.5, PM10 and respirable fraction measurements in this working environment without wind.

Choosing the number of images and image position when analyzing the UNC Passive Aerosol Sampler for occupational exposure assessment

“…Data for this study came from UNC sampler analyses made previously, [5] analyzing 60 images covering an area of 16.2 mm 2 . Brief descriptions of sampling and analysis are given below.…”

“…More details are provided in the previous article. [5] Sampling Stationary sampling was made at four locations in an open pit mine: crushing station, drive station, concentrator, and concentrate terminal. The sampling time at each location was 8 hr in the evening, night, and morning respectively to follow the workers' shifts.…”

“…The setup, storage, handling, and concentration calculations have previously been described by Shirdel et al [5] In short, the UNC samplers were placed in shelters (RJ Lee Group, Monroeville, PA), which were grounded. Before and after sampling, the UNC samplers were kept in protective holders.…”

“…[2][3][4] In a previous study, the UNC sampler was compared with commonly used aerosol sampling methods in a working environment and was found useful but one of the drawbacks was the analysis time. [5] Imaging the collection surface of one sampler with a manual scanning electron microscope (SEM) takes about 1.5 hr with Â500 magnification. [5] Computer-controlled SEM with energy dispersive spectroscopy (EDS) of the UNC sampler with x600 magnification has been reported to take about 1 hr.…”

“…[5] Imaging the collection surface of one sampler with a manual scanning electron microscope (SEM) takes about 1.5 hr with Â500 magnification. [5] Computer-controlled SEM with energy dispersive spectroscopy (EDS) of the UNC sampler with x600 magnification has been reported to take about 1 hr. [6] Previous studies have focused on the effect of particle count on precision.…”