Christian Monz

Comparability of Portable Nanoparticle Exposure Monitors

Five different portable instrument types to monitor exposure to nanoparticles were subject to an intensive intercomparison measurement campaign. Four of them were based on electrical diffusion charging to determine the number concentration or lung deposited surface area (LDSA) concentration of airborne particles. Three out of these four also determined the mean particle size. The fifth instrument type was a handheld condensation particle counter (CPC). The instruments were challenged with three different log-normally distributed test aerosols with modal diameters between 30 and 180 nm, varying in particle concentration and morphology. The CPCs showed the highest comparability with deviations on the order of only ±5%, independent of the particle sizes, but with a strictly limited upper number concentration. The diffusion charger-based instruments showed comparability on the order of ±30% for number concentration, LDSA concentration, and mean particle size, when the specified particle size range of the instruments matched the size range of the aerosol particles, whereas significant deviations were found when a large amount of particles exceeded the upper or lower detection limit. In one case the reported number concentration was even increased by a factor of 6.9 when the modal diameter of the test aerosol exceeded the specified upper limit of the instrument. A general dependence of the measurement accuracy of all devices on particle morphology was not detected.

On the effect of wearing personal nanoparticle monitors on the comparability of personal exposure measurements

Personal inhalation exposures to airborne agents, including nanomaterials, are ideally measured in the breathing zone, using personal monitors or samplers. It is known from previous studies that the available personal monitors can measure airborne nanomaterial concentrations under laboratory conditions with an accuracy and comparability of ±30% or better. However, it is unclear whether this level of accuracy and comparability can also be achieved when these instruments are used as personal monitoring devices by individuals carrying out a wide variety of activities. In the present study, we investigated the reliability of DiSCmini and Partector during simulated exposure measurements. Two individuals were equipped with two identical instruments each, one mounted near the left and the other near the right collarbone. Both individuals went through a sequence of pre-determined and controlled activities, while simultaneously being exposed to well-defined NaCl aerosols within a 23 m3 chamber. A third specimen of both instruments was placed on a table in the middle of the chamber. The results of the Partector, mounted directly on the left or right side lapel within the personal breathing zone, agreed very well with each other and with the results from the third Partector on the table. The deviations were typically within ±10%. The scatter of the data was found to be larger when the individuals were walking than when they were sitting but the average concentrations remained unaffected by the activities. It can hence be concluded that the positioning of the sampling inlet within the breathing zone does not affect the measurement result, independent of personal activities and whether the carrying person is left- or right-handed. In contrast, the DiSCmini results showed very large deviations of up to a factor of three. However, this was caused by the use of silicone tubes in order to sample air from the personal breathing zone and transport to the belt mounted instruments. Siloxanes degas from the tubes into the airflow and are ionized in the unipolar diffusion charger of the DiSCmini and hence change the charging characteristics significantly affecting the measurement results.

Inter-comparison of personal monitors for nanoparticles exposure at workplaces and in the environment

Personal monitors based on unipolar diffusion charging (miniDiSC/DiSCmini, NanoTracer, Partector) can be used to assess the individual exposure to nanoparticles in different environments. The charge acquired by the aerosol particles is nearly proportional to the particle diameter and, by coincidence, also nearly proportional to the alveolar lung-deposited surface area (LDSA), the metric reported by all three instruments. In addition, the miniDiSC/DiSCmini and the NanoTracer report particle number concentration and mean particle size. In view of their use for personal exposure studies, the comparability of these personal monitors was assessed in two measurement campaigns. Altogether 29 different polydisperse test aerosols were generated during the two campaigns, covering a large range of particle sizes, morphologies and concentrations. The data provided by the personal monitors were compared with those obtained from reference instruments: a scanning mobility particle sizer (SMPS) for LDSA and mean particle size and a ultrafine particle counter (UCPC) for number concentration. The results indicated that the LDSA concentrations and the mean particle sizes provided by all investigated instruments in this study were in the order of ±30% of the reference value obtained from the SMPS when the particle sizes of the test aerosols generated were within 20-400nm and the instruments were properly calibrated. Particle size, morphology and concentration did not have a major effect within the aforementioned limits. The comparability of the number concentrations was found to be slightly worse and in the range of ±50% of the reference value obtained from the UCPC. In addition, a minor effect of the particle morphology on the number concentration measurements was observed. The presence of particles >400nm can drastically bias the measurement results of all instruments and all metrics determined.

Development and Evaluation of a Nanoparticle Generator for Human Inhalation Studies with Airborne Zinc Oxide

In the EU there is an increasing need for regulatory agencies to derive health based threshold limits based on human inhalation studies with airborne particles. A necessary prerequisite for such projects is the development of a suitable generator system to produce nanoparticle test aerosols for human whole-body inhalation studies. We decided to use a generator with flame-based heating of aqueous precursor solutions. Validation of the test system was done by generating zinc oxide (ZnO) nanoparticles with minimal contamination of trace gases, i.e., nitric oxides or carbon monoxide that could confound the effects seen in exposed subjects. ZnO was selected based on the uncertainties surrounding its health effects after exposure at the workplace. The generation process of the developed flame generator yields ZnO nanoparticles with monomodal size distribution and very good temporal stability. The maximum target exposure mass concentration of 2 mg/m3 ZnO, with a resulting median particle diameter of 57 nm, is attainable in our human exposure laboratory. The morphological examination shows typical agglomerates and aggregates formed by high temperature processes. Overall, the performed experiments confirm that a constant exposure can be provided for all subjects at all times. Copyright 2014 American Association for Aerosol Research