Use of a Condensation Particle Counter and an Optical Particle Counter to Assess the Number Concentration of Engineered Nanoparticles

Abstract

There is a need to evaluate nanoparticle (< 100 nm) exposures in occupational settings. However, portable instruments do not size segregate particles in that size range. A proxy method for determining nanoparticle count concentrations involves subtracting counts made with a condensation particle counter (CPC) from those of an optical particle counter/sizer (OPC), resulting in an estimation of "very fine" particles < 300 nm, where 300 nm is the OPC lower detection limit. However, to determine size distributions from which particles < 100 nm may be estimated, the resulting count of particles < 300 nm can be used as an additional channel of count data in addition to those obtained from the OPC. To test these methods, the very fine number concentrations determined using a CPC and OPC were compared with those from SMPS measurements and were used to verify the accuracy of a very fine particle number concentration determined by an OPC and CPC. Two "size-distribution" methods, weighted-average and log-probit, were applied to reproduce particle size distributions from OPC and CPC data and were then evaluated relative to their ability to accurately estimate the nanoparticle number concentrations. Various engineered nanoparticles were used to create test aerosols, including titanium dioxide (TiO(2)), silicon dioxide (SiO(2)), and iron oxide (Fe(2)O(3)). These materials were chosen because of their different refractive indices and therefore may be measured differently by the OPC. The count-difference method was able to estimate very fine particle number concentrations with an error between 10.9 to 58.4%. In estimating nanoparticle number concentrations using the size-distribution methods, the log-probit method resulted in the lowest percent errors that ranged from -42% to 1023%. Percent error was lower than the instrument manufacturer's indicated level of accuracy when the test aerosol refractive index was similar to that used for OPC calibration standards. Accuracy could be increased if there was an increase in the size resolution for number concentrations measured by the CPC of very fine particles and mitigation of optical effects.

Evaluation of the Potential Airborne Release of Carbon Nanofibers During the Preparation, Grinding, and Cutting of Epoxy-Based Nanocomposite Material

“…(21) Also, non-spherical particles and agglomeration state may cause variability in the precision and accuracy of optical-based counting instruments. (22) However, trends involving increases in particle number concentration or aerosol mass concentration associated with specific tasks can be identified.…”

Assessment of Two Portable Real-Time Particle Monitors Used in Nanomaterial Workplace Exposure Evaluations

“…Measurements obtained by the simultaneous use of both a CPC and an OPC have been used by researchers to calculate particle number concentrations less than 300 nm (referred to as very fine particles) by subtracting concentrations of 300 to 1000 nm particles measured by an OPC from particle concentrations from a CPC (10 to 1000 nm) [5], [21]. It was estimated that this count difference method was able to estimate very fine particle number concentrations with an error between 10.9 to 58.4% [22]. Our results showed similar agreement limits (7.6% to 52.9%) between measurements by the SMPS and the mean difference method in measuring very fine particle number concentrations.…”

Occupational Exposure to Airborne Nanomaterials: An Assessment of Worker Exposure to Aerosolized Metal Oxide Nanoparticles in Semiconductor Wastewater Treatment

“…(10) Exposure sampling data collected between February 2013 and April 2014 in the WWT area are reported and analyzed in this article. Air monitoring methodology draws from the framework proposed for distinguishing ENMs from incidental sources and determining number concentration, (33)(34) and applies exposure monitoring guidelines set forth by AIHA (32) and the Nanoparticle Emission Assessment Technique (NEAT) established by NIOSH. (35)(36) The sampling approach for airborne exposures is depicted in Figure 3.…”