Martin Fierz

Design, Calibration, and Field Performance of a Miniature Diffusion Size Classifier

Due to the increasingly widespread use of engineered nanoparticles and the increasing number of persons handling them, there is a need to monitor the personal exposure of these persons. Current gravimetric and optic methods are rather insensitive for nanoparticles ( <∼ 100 nm), and therefore not suitable for this task. To help solve this problem, we have miniaturized an instrument capable of measuring nanoparticles developed earlier by our group; the diffusion size classifier (DiSC). The instrument is now handheld (4 × 9 × 18 cm), and can easily be used for personal exposure monitoring, opening up applications for workplace exposure monitoring (for engineered nanoparticles but also for traditional workplace aerosols such as welding fumes or combustion exhaust) and medical studies. The DiSC measures the particle number concentration and the average particle diameter of an aerosol, however, like most simple instruments, it is nonspecific, i.e., it detects all nanoparticles and cannot distinguish between background aerosol and specific engineered nanoparticles. In this paper, we first present the instrument design and the calibration procedure for the miniature DiSC, followed by some results from comparisons with traditional aerosol instruments in the field.

Pushing the spatio-temporal resolution limit of urban air pollution maps

Up-to-date information on urban air pollution is of great importance for health protection agencies to assess air quality and provide advice to the general public in a timely manner. In particular, ultrafine particles (UFPs) are widely spread in urban environments and may have a severe impact on human health. However, the lack of knowledge about the spatio-temporal distribution of UFPs hampers profound evaluation of these effects. In this paper, we analyze one of the largest spatially resolved UFP data set publicly available today containing over 25 million measurements. We collected the measurements throughout more than a year using mobile sensor nodes installed on top of public transport vehicles in the city of Zurich, Switzerland. Based on these data, we develop land-use regression models to create pollution maps with a high spatial resolution of 100m × 100 m. We compare the accuracy of the derived models across various time scales and observe a rapid drop in accuracy for maps with subweekly temporal resolution. To address this problem, we propose a novel modeling approach that incorporates past measurements annotated with metadata into the modeling process. In this way, we achieve a 26% reduction in the root-mean-square error-a standard metric to evaluate the accuracy of air quality models-of pollution maps with semi-daily temporal resolution. We believe that our findings can help epidemiologists to better understand the adverse health effects related to UFPs and serve as a stepping stone towards detailed real-time pollution assessment.

Real-time measurement of aerosol size distributions with an electrical diffusion battery

Abstract The ‘electrical diffusion battery’ is a new device for measuring aerosol size distributions with low size resolution but with a time resolution of a few seconds. The device consists of a diffusion charger, followed by a screen-type diffusion battery with electronically insulated stages. We present results and comparisons with SMPS data from both laboratory experiments and from emission measurements of a diesel vehicle on a chassis dynamometer. A fairly good agreement between the two results is obtained.

Field Measurement of Particle Size and Number Concentration with the Diffusion Size Classifier (Disc)

The Diffusion Size Classifier (DiSC) is a new instrument to measure number concentration and average diameter of nanometer sized particles in the size range 10 200nm. It is small, easily portable and battery operated and therefore well suited for field measurements. The measurement range is suitable for ambient air concentrations (1000 – 500000 particles/cm); together with a diluter it can be used for emission measurements. The number concentrations measured with DiSC agree well with those measured with a condensation particle counter. The response time is short enough to measure transient engine operation. The DiSC is therefore a useful instrument for number concentration measurements in non-laboratory settings.

Theoretical and Experimental Evaluation of a Portable Electrostatic TEM Sampler

In this study, we present the design, calibration, and performance evaluation of a portable TEM sampler to collect ultrafine particles on TEM grids. The sampler is based on electrostatic deposition. We performed calibration experiments with monodisperse model particles of different size, morphology, and chemistry to evaluate the efficiency of the device. Additionally, we modeled the performance of the TEM sampler using finite element calculations to calculate the sampling efficiency as function of particle size. We find a good agreement between the model calculations and calibration experiments, but with a systematic deviation of about 30%. We present further experiments with polydisperse particles and derive particle size distributions and absolute number concentrations from TEM images. The shape of the size distribution is very similar to the corresponding SMPS measurements, while the total number concentration has a larger uncertainty. Thanks to the compact design of the sampler, it can be used to collect ultrafine particles even in remote or hostile environments, where no electric power is available.

Exposure to engineered nanoparticles: Model and measurements for accident situations in laboratories

In the life cycle of engineered nanoparticles (ENP), their manufacturing requires particular attention because of unwanted potential ENP emissions to workplaces. We simulated three scenarios of equipment failure during gas phase production of nanoparticles in a laboratory. The emission plume of nanoparticles was tracked with high spatial and temporal resolution by 10 measurement devices. While under normal production conditions, no elevated ENP concentrations were observed, worst case scenarios led to homogeneous indoor ENP concentrations of up to 10(6)cm(-3) in a 300m(3) production room after only 60s. The fast dispersal in the room was followed by an exponential decrease in number concentration after the emission event. Under conditions like those observed - rapid dispersal and good mixing - a single measurement device alone can provide valuable information for an ENP exposure assessment. A one-box model adequately reflected measured number concentrations (r(2)>0.99). The ENP emission rates to the workplace were estimated between 2.5·10(11) and 6·10(12)s(-1) for the three emission scenarios. The worst case emission rate at the production zone was also estimated at 2·10(13)s(-1) with a stoichiometric calculation based on the precursor input, density and particle size. ENP intake fractions were 3.8-5.1·10(-4) inhaled ENP per produced ENP in the investigated setting. These could only be substantially lowered by leaving the production room within a few minutes after the emission event.

Aerosol Measurement by Induced Currents

We introduce a new electrical measurement technique for aerosol detection, based on pulsed unipolar charging followed by a non-contact measurement of the rate of change of the aerosol space charge in a Faraday cage. This technique, which we call “aerosol measurement with induced currents,” has some advantages compared to the traditional method of collecting the charged particles on either an electrode or with a particle filter. We describe the method and illustrate it with a simple and miniature (shirt-pocket-sized) instrument to measure lung-deposited surface area. Aerosol measurement by induced currents can also be applied to more complex devices. Copyright 2014 American Association for Aerosol Research

Limitations in the Use of Unipolar Charging for Electrical Mobility Sizing Instruments: A Study of the Fast Mobility Particle Sizer

A comparison between three different types of particle sizing instruments (fast mobility particle sizer, FMPS; electrical low pressure impactor, ELPI; and scanning mobility particle sizer, SMPS) and one condensation particle counter (CPC) was made to compare instrument response in terms of size distributions and number concentration. Spherical oil droplets in 39 different sizes, with geometric mean diameter (GMD) ranging from 50 nm to 820 nm, were used as test particles. Furthermore, a characterization of the FMPS unipolar charger behavior was made to analyze the measured size distributions and number concentrations. The results show that all three sizing-instruments agree well for particle sizes below 200 nm, both in terms of size and number concentration, but the FMPS deviates clearly when particle sizes exceed 200 nm. Above this, the FMPS underestimates the particle size throughout the remainder of the size range, with an apparent upper limit for GMD of 300 nm. It also estimates a higher particle number concentration as compared to the other instruments. Analysis of the 22 FMPS electrometer currents and calculation of average number of charges per particle show a diameter dependence of response of for the FMPS unipolar charger. The resulting calculated electrical mobility showed a minimum in mobility for spherical particles at 577 nm, which indicates an interfering range of particles above the measurement range, but below the cut-off of the inlet pre-separator (1 μm). The study concludes that particle distributions with a true GMD above 200 nm cannot be measured reliably with the FMPS. Copyright 2015 American Association for Aerosol Research

Nano Aerosol Chamber for In-Vitro Toxicity (NACIVT) studies

Abstract Inhalation of ambient air particles or engineered nanoparticles (NP) handled as powders, dispersions or sprays in industrial processes and contained in consumer products pose a potential and largely unknown risk for incidental exposure. For efficient, economical and ethically sound evaluation of health hazards by inhaled nanomaterials, animal-free and realistic in vitro test systems are desirable. The new Nano Aerosol Chamber for in-vitro Toxicity studies (NACIVT) has been developed and fully characterized regarding its performance. NACIVT features a computer-controlled temperature and humidity conditioning, preventing cellular stress during exposure and allowing long-term exposures. Airborne NP are deposited out of a continuous air stream simultaneously on up to 24 cell cultures on Transwell® inserts, allowing high-throughput screening. In NACIVT, polystyrene as well as silver particles were deposited uniformly and efficiently on all 24 Transwell® inserts. Particle–cell interaction studies confirmed that deposited particles reach the cell surface and can be taken up by cells. As demonstrated in control experiments, there was no evidence for any adverse effects on human bronchial epithelial cells (BEAS-2B) due to the exposure treatment in NACIVT. The new, fully integrated and transportable deposition chamber NACIVT provides a promising tool for reliable, acute and sub-acute dose-response studies of (nano)particles in air-exposed tissues cultured at the air–liquid interface.

Review of measurement techniques and methods for assessing personal exposure to airborne nanomaterials in workplaces

Exposure to airborne agents needs to be assessed in the personal breathing zone by the use of personal measurement equipment. Specific measurement devices for assessing personal exposure to airborne nanomaterials have only become available in the recent years. They can be differentiated into direct-reading personal monitors and personal samplers that collect the airborne nanomaterials for subsequent analyses. This article presents a review of the available personal monitors and samplers and summarizes the available literature regarding their accuracy, comparability and field applicability. Due to the novelty of the instruments, the number of published studies is still relatively low. Where applicable, literature data is therefore complemented with published and unpublished results from the recently finished nanoIndEx project. The presented data show that the samplers and monitors are robust and ready for field use with sufficient accuracy and comparability. However, several limitations apply, e.g. regarding the particle size range of the personal monitors and their in general lower accuracy and comparability compared with their stationary counterparts. The decision whether a personal monitor or a personal sampler shall be preferred depends strongly on the question to tackle. In many cases, a combination of a personal monitor and a personal sampler may be the best choice to obtain conclusive results.