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There is great concern regarding the adverse health implications of engineered nanoparticles. However, there are many circumstances where the production of incidental nanoparticles, i.e., nanoparticles unintentionally generated as a side product of some anthropogenic process, is of even greater concern. In this study, metal-based incidental nanoparticles were measured in two occupational settings: a machining center and a foundry. On-site characterization of substrate-deposited incidental nanoparticles using a field-portable X-ray fluorescence provided some insights into the chemical characteristics of these metal-containing particles. The same substrates were then used to carry out further off-site analysis including single-particle analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Between the two sites, there were similarities in the size and composition of the incidental nanoparticles as well as in the agglomeration and coagulation behavior of nanoparticles. In particular, incidental nanoparticles were identified in two forms: submicrometer fractal-like agglomerates from activities such as welding and supermicrometer particles with incidental nanoparticles coagulated to their surface, herein referenced as nanoparticle collectors. These agglomerates will affect deposition and transport inside the respiratory system of the respirable incidental nanoparticles and the corresponding health implications. The studies of incidental nanoparticles generated in occupational settings lay the groundwork on which occupational health and safety protocols should be built. [ABSTRACT FROM AUTHOR]

Conventional methods to measure the metallic content of particles by size are time consuming and expensive, requiring collection of particles with a cascade impactor and subsequent metals analysis by inductively coupled plasma mass spectrometry (ICP-MS). In this work, we describe a rapid way to measure the size distribution of metal-containing particles from 10 nm to 20 µm, using a nano micro-orifice uniform-deposit impactor (nano-MOUDI) to size-selectively collect particles that are then analyzed with a field portable X-ray fluorescence (FP-XRF) device to determine metal composition and concentration. The nano-MOUDI was used to sample a stainless-steel aerosol produced by a spark discharge system. The particle-laden substrates were then analyzed directly with FP-XRF and then with ICP-MS. Results from FP-XRF were linearly correlated with results from ICP-MS (R2= 0.91 for Fe andR2= 0.84 for Cr). Although the FP-XRF was unable to effectively detect Fe particles at mass per substrate loadings less than 2.5 µg effectively, it produced results similar to those from ICP-MS at a mass per substrate loadings greater than 2.5 µg. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Porous polyurethane foam was evaluated to replace the eight nylon meshes used as a substrate to collect nanoparticles in the Nanoparticle Respiratory Deposition (NRD) sampler. Cylindrical (25 mm diameter by 40 mm deep) foam with 100 pores per inch was housed in a 25-mm-diameter conductive polypropylene cassette cowl compatible with the NRD sampler. Pristine foam and nylon meshes were evaluated for metals content via elemental analysis. The size-selective collection efficiency of the foam was evaluated using salt (NaCl) and metal fume aerosols in independent tests. Collection efficiencies were compared to the nanoparticulate matter (NPM) criterion and a semi-empirical model for foam. Changes in collection efficiency and pressure drop of the foam and nylon meshes were measured after loading with metal fume particles as measures of substrate performance. Substantially less titanium was found in the foam (0.173 µg sampler−1) compared to the nylon mesh (125 µg sampler−1), improving the detection capabilities of the NRD sampler for titanium dioxide particles. The foam collection efficiency was similar to that of the nylon meshes and the NPM criterion (R2= 0.98, for NaCl), although the semi-empirical model underestimated the experimental efficiency (R2= 0.38). The pressure drop across the foam was 8% that of the nylon meshes when pristine and changed minimally with metal fume loading (∼19 mg). In contrast, the pores of the nylon meshes clogged after loading with ∼1 mg metal fume. These results indicate that foam is a suitable substrate to collect metal (except for cadmium) nanoparticles in the NRD sampler. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) particles, including nanoparticles with diameters smaller than 100 nm, are used extensively in consumer products. In a 2011 current intelligence bulletin, the National Institute of Occupational Safety and Health (NIOSH) recommended methods to assess worker exposures to fine and ultrafine TiO2 particles and associated occupational exposure limits for these particles. However, there are several challenges and problems encountered with these recommended exposure assessment methods involving the accurate quantitation of titanium dioxide collected on air filters using acid digestion followed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, recommended digestion methods include the use of chemicals, such as perchloric acid, which are typically unavailable in most accredited industrial hygiene laboratories due to highly corrosive and oxidizing properties. Other alternative methods that are used typically involve the use of nitric acid or combination of nitric acid and sulfuric acid, which yield very poor recoveries for titanium dioxide. Therefore, given the current state of the science, it is clear that a new method is needed for exposure assessment. In this current study, a microwave-assisted acid digestion method has been specifically designed to improve the recovery of titanium in TiO2 nanoparticles for quantitative analysis using ICP-OES. The optimum digestion conditions were determined by changing several variables including the acids used, digestion time, and temperature. Consequently, the optimized digestion temperature of 210°C with concentrated sulfuric and nitric acid (2:1 v/v) resulted in a recovery of >90% for TiO2. The method is expected to provide for a more accurate quantification of airborne TiO2 particles in the workplace environment. [ABSTRACT FROM AUTHOR]

A granular bed was designed to collect nanoparticles as an alternative to nylon mesh screens for use in a nanoparticle respiratory deposition (NRD) sampler. The granular bed consisted of five layers in series: a coarse mesh, a large-bead layer, a small-bead layer, a second large-bead layer, and a second coarse mesh. The bed was designed to primarily collect particles in the small-bead layer, with the coarse mesh and large-bead layers designed to hold the collection layer in position. The collection efficiency of the granular bed was measured for varying depths of the small-bead layer and for test particles with different shape (cuboid, salt particles; and fractal, and stainless steel and welding particles). Experimental measurements of collection efficiency were compared to estimates of efficiency from theory and to the nanoparticulate matter (NPM) criterion, which was established to reflect the total deposition in the human respiratory system for particles smaller than 300 nm. The shape of the collection efficiency curve for the granular bed was similar to the NPM criterion in these experiments. The collection efficiency increased with increasing depth of the small-bead layer: the particle size associated with 50% collection efficiency,d50, for salt particles was 25 nm for a depth of 2.2 mm, 35 nm for 3.2 mm, and 45 nm for 4.3 mm. The best-fit to the NPM criterion was found for the bed with a small-bead layer of 3.2 mm. Compared to cubic salt particles, the collection efficiency was higher for fractal-shaped particles larger than 50 nm, presumably due to increased interception. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

This study introduces a spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and concentration of the fume produced and the concentration of ozone (O3) and nitrogen oxides (NOX) were characterized. The number median diameter (NMD) and total number concentration (TNC) of fresh fume particles were ranged 10–23 nm and 3.1×107− 6×107particles/cm3, respectively. For fresh fume particles, the total mass concentration (TMC) measured gravimetrically ranged 85–760 μg/m3. The size distribution was stable over a period of 12 h. The NMD and TNC of aged fume particles were ranged 81–154 nm and 1.5×106−2.7×106particles/cm3, respectively. The composition of the aged fume particles was dominated by Fe and O with an estimated stoichiometry between that of Fe2O3and Fe3O4. Concentrations of O3and NOXwere ranged 0.07–2.2 ppm and 1–20 ppm, respectively. These results indicate that the SDS is capable of producing stable fumes over a long-period that are similar to actual welding fumes. This system may be useful in toxicological studies and evaluation of instrumentation. Copyright 2014 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Aerosols are important atmospheric constituents as they impact the Earth's energy balance and climate. An analysis of the impact of aerosols depends on the detailed knowledge of aerosol optical properties. However, there is a lack of refractive index data for atmospherically relevant organic compounds in the infrared (IR) region which complicates the quantitative estimation of the aerosol influence on the radiative balance. In this study, we investigate the optical properties of atmospherically relevant carboxylic acids and HUmic-LIke Substances (HULIS) proxies. Aerosol size distributions are measured simultaneously with Fourier transform infrared (FTIR) extinction spectra to calculate the complex refractive index. Scanning electron microscopy (SEM) images are also collected to investigate particle shape. Analysis of SEM images shows evidence for agglomeration in some cases. The experimentally measured IR resonances do not appear to be highly sensitive to agglomeration effects. However, there is an increase in the scattering efficiency at shorter wavelengths as the result of larger overall particle size of the agglomerates. Refractive indices are retrieved from the IR extinction spectra of organic acids and HULIS proxies. Mie simulation results confirm the quality of the retrieved optical constants. Interestingly, the optical constants determined for the acids are in agreement with the published data for fire smoke plumes. Copyright 2014 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Inhalation toxicity studies of nanoparticles require production of test aerosols with a number of acceptable characteristics. Five different generation methods for producing a nanoparticle aerosol from the bulk powder were evaluated with the goal of producing an acceptable aerosol that is homogenous, has a consistent concentration over time in which the magnitude may be intentionally varied, and has a size distribution that is both unimodal and has a small geometric mean diameter relative to the primary particle size of the nanoparticle bulk powder. Four types of bulk powders were evaluated including titanium dioxide, silicon dioxide, polymer-coated silver, and single walled carbon nanotubes. A nebulizer was the only tested method able to produce a consistent aerosol of sufficient magnitude. However, the resulting aerosol contains particles derived from the carrier water. Prior sonication of the nanoparticle suspension alone was found to be not useful for deagglomerating nanoparticles. [ABSTRACT FROM AUTHOR]

We examined pulmonary inflammatory responses of mice following whole-body inhalation exposure to copper and iron nanoparticles in acute and sub-acute studies. Concentrations for sub-acute copper and iron exposures were 3.6 mg m-3. No significant pathology was found following acute exposure. Immediately following sub-acute exposure, both iron- and copper-exposed mice showed increased inflammation compared to sentinels. Copper nanoparticle-exposed mice had significantly higher lavage cytokines as well as perivasculitis and alveolitis. Three weeks post-exposure, all inflammatory markers decreased for iron nanoparticle-exposed mice, however, some remained elevated for copper-exposed mice. At biologically relevant pHs, in vitro studies showed that copper nanoparticles displayed a greater propensity for dissolution compared to iron. We conclude that the presence of dissolved ions, the concomitant formation of smaller nanoparticles and the absence of particles in stained lung sections immediately postexposure (inferring either translocation or more dispersed aerosol distribution) contributed to the increased inflammation observed in copper nanoparticle-exposed mice. [ABSTRACT FROM AUTHOR]

Heterogeneous reactions of trace gases with mineral dust aerosol not only impact the chemical balance of the atmosphere but also the physicochemical properties of the dust particle and the ability of the particle to act as a cloud condensation nuclei (CCN). Recent field studies have shown that carbonate minerals are preferentially associated with nitrates whereas aluminum silicates (i.e., clay minerals) are preferentially associated with sulfates. To better understand how this association can impact the climate effects of mineral dust particles, we have measured the CCN activity of a number of pure and internal mixtures of aerosols relevant to these recent field studies. The CCN activity of CaCO3-Ca(NO3)2 aerosol, simulating the activity of mineral dust aerosol that has been partially processed by nitrogen oxides in the atmosphere, is significantly enhanced relative to CaCO3 aerosol of the same diameter. Similar results are obtained for a clay mineral, kaolinite, internally mixed with (NH4)2SO4. For example, at 0.3% supersaturation, a 200 nm particle containing a soluble nitrate or sulfate component is 2 to 4 times more active than an unreacted particle. The results presented here show that when determining the contribution of mineral dust aerosol to the overall impact of the aerosol indirect effect on radiative forcing, changes in chemical composition due to atmospheric processing cannot be ignored. [ABSTRACT FROM AUTHOR]

TiO2 is a widely used manufactured nanomaterial and the opportunity for human exposure makes it necessary to study its health implications. Using murine models for inflammation, size effects of inflammatory response in instillation and acute inhalation exposures of TiO2 nanoparticles with manufacturers' average particles sizes of 5 and 21 nm were investigated. The properties of the primary nanoparticles, nanoparticle agglomerates aerosol and instillation solution for both sized nanoparticles were evaluated. Mice were acutely exposed in a whole-body exposure chamber or through nasal instillation and toxicity was assessed by enumeration of total and differential cells, determination of total protein, LDH activity and inflammatory cytokines in BAL fluid. Lungs were also evaluated for histopathological changes. Results show the larger TiO2 nanoparticles were found to be moderately, but significantly, more toxic. The nanoparticles had different agglomeration states which may be a factor as important as the surface and physical characteristics of the primary nanoparticles in determining toxicity. [ABSTRACT FROM AUTHOR]

Although atmospheric particles are often non-spherical, Mie theory is commonly used to acquire aerosol optical depth, composition, and transport information from satellite retrievals. In the infrared (IR) region, the radiative effects of aerosols, usually modeled with Mie theory, are subtracted from satellite spectral data to determine key atmospheric and oceanic properties. To gain a better understanding of the infrared radiative effects of aerosols and the methods used to model them, an instrument has been designed to simultaneously measure infrared extinction spectra and particle size distributions obtained from a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). Infrared extinction spectra are simulated with Mie theory using the measured particle size distributions and available literature optical constants. As a result, the errors associated with using Mie theory to model the infrared extinction of mineral dust aerosol can be quantitatively examined. Initial results for this instrument are presented here. For ammonium sulfate, the Mie theory simulation is in good agreement with our measured extinction spectrum. This is in accordance with the nearly spherical shape of ammonium sulfate particles. However, for illite, an abundant clay mineral, there is poor agreement between the experimental spectrum and the Mie simulation. This result is attributed to particle shape effects. [ABSTRACT FROM AUTHOR]

The role of heterogeneous reactions of trace atmospheric gases on solid aerosol surfaces in the troposphere is not well understood. In this review, the heterogeneous chemistry of nitrogen oxides and volatile organic compounds on the surface of atmospherically relevant particles such as oxides, soot, carbonates and mineral dust is discussed. The approach to unravelling both the molecular level details and the global significance of these reactions is one that combines laboratory investigations and atmospheric chemistry models. The laboratory investigation utilizes spectroscopic measurements to provide an understanding of the details of the chemistry that occurs in the gas phase and on the surface of the particle together with kinetic measurements in order to quantify the rates of these reactions. These fundamental measurements provide a basis for understanding the detailed molecular level physical chemistry of atmospheric processes. The kinetic data, together with the details provided by the spectroscopic studies, are incorporated into atmospheric chemistry models in order to gain a greater understanding of the role that heterogeneous chemistry plays in the chemical balance of the troposphere. Several examples from the present author's laboratory are discussed in this review. These examples include: (i) the heterogeneous uptake and reactivity of nitrogen oxides (nitrogen dioxide and nitric acid) on oxide and dust particles; (ii) the role of water in the heterogeneous uptake of nitric acid on oxide, carbonate and dust particles; (iii) the heterogeneous production of nitrous acid on silica and soot particles; and (iv) the heterogeneous uptake and reactivity of acetone and other carbonyl compounds on oxide and mineral dust particles. [ABSTRACT FROM AUTHOR]