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

Using low cost open-face passive samplers to sample PM concentration and elemental composition in childcare facilities

Effective, low noise and low-cost samplers for airborne particulate matter (PM) in indoor environments are needed. In 15 northern California childcare facilities, we deployed open-faced polycarbonate substrate passive aerosol samplers and analyzed them using computer-controlled scanning electron microscopy to measure indoor PM particle size, number, and elemental concentration. Particle concentrations were compared to PM concentrations measured by filter-based active samplers. The PM mass concentrations measured after open-faced passive sampling were in good agreement with the PM concentrations obtained using co-located active samplers. The measured PM2.5 concentrations inside of the childcare facilities were in the range of 6-31 μg m-3, while the PM10 concentrations were in the range of 17-96 μg m-3. For PM10, 93.3% of the passive sampler results were within ±30% of those determined with the active sampler, and 67% of the PM2.5 results fell within ±30% of the active sampler measurements. The Pearson's correlation coefficient between PM mass concentrations estimated from the open-faced passive aerosol sampler (OPS) versus gravimetric (active sampler) methods was 0.77 for PM2.5 and 0.95 for PM10, respectively, indicating a strong correlation between the passive and active sampler results. PM and elemental composition varied by facility location and interior characteristics of the childcare facilities such as floor type, presence of combustion sources, occupant density, and the level of activity. The rich carbon content in the polycarbonate substrate produced positive bias in the carbon concentration analysis. Based on the carbon concentration, determined using a copper substrate, a correction factor was needed to determine the total carbon concentrations in the sampled PM for the polycarbonate substrate passive sampler. Overall, the results demonstrated that the OPS collected enough aerosol particles in one business day (6-8 hours) to assess PM levels.

Passive personal air sampling of dust in a working environment-A pilot study

The aim of this study was to make a preliminary evaluation of the University of North Carolina passive aerosol sampler (UNC sampler) for personal air sampling of particles. Nine personal air samplings of respirable fraction were conducted in an open-pit mine, with pairwise UNC samplers and a respirable cyclone mounted on the chest of workers. UNC samples were analyzed with scanning electron microscopy (SEM) and to some extent energy dispersive X-ray spectroscopy (EDS). Respirable cyclone filter samples were weighed. Correlations and particle elemental compositions were described. Microscopic imaging of the collection surface showed that the particles were heterogeneously deposited across the surface of the UNC sampler. Collected particles were shaped as gravel particles and the resulting particle size distribution in air showed a peak at ca. 3 µm aerodynamic diameter, similarly to what has previously been reported from the same mine. The elemental composition indicated mineral origin. All correlations between the airborne mass concentrations from UNC samplers and respirable cyclones (Pearson = 0.54 and Spearman = 0.43) and between pairs of parallel UNC samplers (Pearson = 0.55 and Spearman = 0.67) were weak. The UNC sampler mass concentrations were approximately 30 times higher than those measured with the respirable cyclone. In conclusion, the UNC sampler, when used for personal sampling in a mine, provides a reasonable particle size distribution and the deposited particles appeared to be of mineral origin and not from textile or skin but the approximately 30-fold overestimation of mass concentrations when comparing with respirable cyclone sampling indicates that further improvements are necessary. Positioning of the sampler may be critical and moving the UNC sampler from the chest to e.g. the top of a helmet might be an improvement. Grounding of the sampler in order to avoid static electricity might also be useful. The UNC sampler should continue to be researched for personal sampling, as passive sampling might become a useful alternative to more laborious sampling techniques.

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

The University of North Carolina passive aerosol sampler (UNC sampler) could be an alternative when measuring occupational dust exposure, but the time required for microscopic imaging of the sampler needs to be reduced to make it more attractive. The aims of this study were to (1) characterize the effect on precision when reducing imaging, in order to shorten analysis time and (2) assess if the position of the images makes a difference. Eighty-eight samplers were deployed in different locations of an open pit mine. Sixty images were captured for each UNC sampler, covering 51% of its collection surface, using scanning electron microscopy. Bootstrapped samples were generated with different image combinations, to assess the within-sampler coefficient of variation (CV_ws) for different numbers of images. In addition, the particle concentration relative to the distance from the center of the sampler was studied. Reducing the number of images collected from the UNC sampler led to up to 8.3% CV_ws for 10 images when calculating respirable fraction. As the overall CV has previously been assessed to 36%, the additional contribution becomes minimal, increasing the overall CV to 37%. The mean concentrations of the images were modestly related to distance from the center of the sampler. The CV_ws changed from 8.26% to 8.13% for 10 images when applying rules for the image collection based on distance. Thus, the benefit of these rules on the precision is small and the images can therefore be chosen at random. In conclusion, reducing the number of images analyzed from 60 to 10, corresponding to a reduction of the imaged sampling area from 51% to 8.5%, results in a negligible loss in precision for respirable fraction dust measurements in occupational environments.