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Size-segregated sampling of particulate matter (PM) using impactor suffers from D50 cutoff shift due to particle loading and re-entrainment problems. Cyclonic separation is a viable option to overcome the above problem. However, conventional reverse flow cyclone design having a single inlet and upward-facing outlet also presents a common issue of sample (particle) loss during sampling and requires several arrangements to convert it into an efficient PM sampler. Therefore, here we present a high-volume (HV) PM10 multi-inlet cyclone (MIC) design with a downward-facing outlet, which overcomes existing problems and has additional advantages, such as omnidirectional sampling where a filter collector is placed in a straight line below the cyclone outlet to minimize sample loss. Moreover, like the existing USEPA reference low-volume PM2.5 sampler inlet design, which consists of 2-impactor stages (PM10 followed by PM2.5) in a straight path, this developed HV PM10 MIC sampler can accommodate a second size fractionator (e.g., PM2.5 impactor) to sample finer-size PM on a filter. D50 cutoff of developed PM10 MIC is numerically and experimentally investigated. Since the study regarding cutoff size of another type PM10 cyclone, called respirable dust sampler (RDS) is not available in the public domain and is widely used for PM10 monitoring in India, we investigated its cutoff size empirically and experimentally, and also performed field comparisons. Collocating field evaluation of PM10 MIC and PM10 RDS cyclone was done under a wide range of particle mass loading, and results were compared with USEPA-approved high-volume PM10 impactor sampler and with a real-time particle sizer. The D50 cutoff of PM10 MIC is experimentally achieved to be 9.89 ± 0.3 µm, which is close to 9.94 µm predicted numerically and lies in the range of 9.5–10.5 µm size measured by others for PM10 impactor sampler (USEPA). The D50 cutoff of the PM10 RDS cyclone is experimentally determined to be 3.56 ± 0.1 µm, which is surprisingly lower than its claimed cutoff of 10 µm mentioned in numerous articles, where it has been used for air quality reporting and studies related to aerosol science. The field comparison correlation of PM10 MIC for PM10-2.5 levels with PM10 sampler (USEPA) (R = 0.99) and particle sizer (R = 0.94) correlated well, and the mean deviations are found to be 6.2% and 3%, respectively. While PM10 (RDS) cyclone poorly correlates (R = 0.67), and the mean deviation is 68%. Overall, the developed PM10 MIC overcomes issues associated with existing impactor and conventional cyclone sampler, and can be a better option for high-volume PM10 sampling, especially under a wide range of ambient conditions particularly where the particle mass loading is consistantly high. [ABSTRACT FROM AUTHOR]

With the increasing interest in manufacturing nano-sized metal particles in large quantities for their numerous applications in industry, medicine and daily life as well as nanotoxicity testing, there is a critical demand to improve methods to generate nanoparticles with controllable nano-size and high number concentrations. Here, a stable method for the generation of zinc oxide nanoparticles (ZnO-NPs), especially for the size below 10 nm, by chemical vapor synthesis (CVS) using quenching air was proposed. The present study found that the oxidation step of Zn vapor in the ZnO-NP formation process is the rate-controlling step. Six conditions were tested with various furnace temperatures, carrier gas and quenching air flow rates in a tubular furnace. The experimental results showed that the quenching air flow rates (1-5 L/min) have a great impact on ZnO-NPs generation and characteristics. The geometric mean diameter of synthesized ZnO-NPs or aggregates was decreased from 15.26 to 3.27 nm, the total number concentration was increased from 2.56 × 107 to 4.28 × 107 #/cm3 and the morphology changed from tetrapod-shaped to isometric-shaped when the quenching air flow rate was increased from 1 to 5 L/min at 1 L/min carrier gas flow rate and 500 °C furnace temperature. The diameter and concentration remained stable with only small fluctuations for 5 h at all test conditions, which is very useful for nanotoxicity testing. The size of ZnO-NPs was decreased below 10 nm when the quenching rate was 11,000 K/s or higher at 1 L/min carrier gas flow rate and 500 °C furnace temperature. The experimental yield of ZnO-NPs was found to be 11.93% at 600 °C furnace temperature and less than 1.5% at 500 °C. The low yield of small ZnO-NPs is mainly attributed to the low conversion ratio of Zn vapor by the oxidation reaction, and convection-diffusion deposition loss of Zn vapor, ZnO vapor and small ZnO-NPs, which needs further improvement for future mass production using CVS method. [ABSTRACT FROM AUTHOR]

A numerical model was used to study the homogeneous nucleation process of dibutyl phthalate (DBP) vapor in a laminar flow diffusion chamber (LFDC); the spatial and temporal evolution of DBP droplet size distribution was governed by the population balance equation (PBE). In the PBE, the nucleation rate was calculated by the self-consistent correction nucleation theory (SCCNT), droplet coagulation, vapor and droplet deposition losses were considered. The simulation results showed that the nucleation rate predicted by the SCCNT improved the underestimation of that predicted by the classical nucleation theory. Due to vapor deposition before nucleation and droplet deposition after nucleation on the wall, the DBP mass loss was severe, accounting for about 86.3% of the total inlet vapor mass, and the droplet size distribution shifted towards larger diameters. The simulation results agreed well with the experimental data in terms of the droplet size distribution and average number concentration at the outlet of the LFDC because of the detailed droplet dynamic, transport and deposition mechanisms treated in this model. Based on this model, the number of molecules in the critical cluster was calculated using the first nucleation theorem and found to be larger about 50% than that calculated using the Gibbs-Thompson equation. [ABSTRACT FROM AUTHOR]

Natural and human activities generate a significant amount of PM (particles ≤2.5 μm in aerodynamic diameter) into the surrounding atmospheric environments. Because of their small size, they can remain suspended for a relatively longer time in the air than coarse particles and thus can travel long distances in the atmosphere. PM is one of the key indicators of pollution and known to cause numerous types of respiratory and lung-related diseases. Due to poor implementation of regulations and a time lag in introducing the vehicle technology, levels of PM in most Asian cities are much worse than those in European environments. Dedicated reviews on understanding the characteristics of PM in Asian urban environments are currently missing but much needed. In order to fill the existing gaps in the literature, the aim of this review article is to describe dominating sources and their classification, followed by current status and health impact of PM, in Asian countries. Further objectives include a critical synthesis of the topics such as secondary and tertiary aerosol formation, chemical composition, monitoring and modelling methods, source apportionment, emissions and exposure impacts. The review concludes with the synthesis of regulatory guidelines and future perspectives for PM in Asian countries. A critical synthesis of literature suggests a lack of exposure and monitoring studies to inform personal exposure in the household and rural areas of Asian environments. [ABSTRACT FROM AUTHOR]

The carbonaceous aerosol concentrations in coarse particle (PM: Dp ≤ 10 μm, particulate matter with an aerodynamic diameter less than 10 μm), fine particle (PM: Dp ≤ 2.5 μm), and ultrafine particle (PM: Dp ≤ 0.133 μm) carbon fractions in a rural area were investigated during haze events in northwestern China. The results indicated that PM contributed a large fraction in PM. OC (organic carbon) accounted for 33, 41, and 62 % of PM, PM, and PM, and those were 2, 2.4, and 0.4 % for EC (elemental carbon) in a rural area, respectively. OC3 was more abundant than other organic carbon fractions in three PMs, and char dominated EC in PM and PM while soot dominated EC in PM. The present study inferred that K, OP, and OC3 are good biomass burning tracers for rural PM and PM, but not for PM during haze pollution. Our results suggest that biomass burning is likely to be an important contributor to rural PMs in northwestern China. It is necessary to establish biomass burning control policies for the mitigation of severe haze pollution in a rural area. [ABSTRACT FROM AUTHOR]

The influence of particle morphology on the accuracy of nanoparticle size distributions measured by the engine exhaust particle sizer spectrometer (EEPS, TSI Model 3090) was studied using the scanning mobility particle sizer (SMPS, TSI Model 3936) as a reference. The EEPS shows higher total number concentrations with the maximum relative difference up to 67 % and smaller number median mobility diameters for polydisperse silver nanoparticles generated in the laboratory. To provide a quantitative explanation of the difference, generated polydisperse nanoparticles were classified as monodisperse particles with the initial equivalent mobility diameter ( d) and sintered in the second furnace at different temperatures (room temperature to 600 °C), to change their morphologies for the comparison tests. Without sintering (room temperature), results show that the measured mobility diameter ( d) of the EEPS is smaller than that measured by the SMPS when d is larger than 30 nm and the difference increases as d is increased from 30 to 300 nm. But the difference decreases as the morphology of particles is changed from branched chain agglomerates to spheres for d less than 80 nm and the sintering temperature higher than 200 °C. Theoretical analysis shows that the mean charge per agglomerates is more than that of spheres resulting in overestimation of the electrical mobility and underestimation of the d by the EEPS. [ABSTRACT FROM AUTHOR]

In this study, nanoalumina and nanoclay particles were compounded separately with ethylene vinyl acetate (EVA) polymer to produce nanocomposites using a twin-screw extruder to investigate exposure and effective controls. Nanoparticle exposures from compounding processes were elevated under some circumstances and were affected by many factors including inadequate ventilation, surrounding air flow, feeder type, feeding method, and nanoparticle type. Engineering controls such as improved ventilation and enclosure of releasing sources were applied to the process equipment to evaluate the effectiveness of control. The nanoparticle loading device was modified by installing a ventilated enclosure surrounding the loading chamber. Exposures were studied using designed controls for comparison which include three scenarios: (1) no isolation; (2) enclosed sources; and (3) enclosed sources and improved ventilation. Particle number concentrations for diameters from 5 to 20,000 nm measured by the Fast Mobility Particle Sizer and aerodynamic particle sizer were studied. Aerosol particles were sampled on transmission electron microscope grids to characterize particle composition and morphology. Measurements and samples were taken at the near- and far-field areas relative to releasing sources. Airborne particle concentrations were reduced significantly when using the feeder enclosure, and the concentrations were below the baseline when two sources were enclosed, and the ventilation was improved when using either nanoalumina or nanoclay as fillers. [ABSTRACT FROM AUTHOR]

A standard rotating drum with a modified sampling train (RD), a vortex shaker (VS), and a SSPD (small-scale powder disperser) were used to investigate the emission characteristics of nano-powders, including nano-titanium dioxide (nano-TiO, primary diameter: 21 nm), nano-zinc oxide (nano-ZnO, primary diameter: 30-50 nm), and nano-silicon dioxide (nano-SiO, primary diameter: 10-30 nm). A TSI SMPS (scanning mobility particle sizer), a TSI APS (aerodynamic particle sizer), and a MSP MOUDI (micro-orifice uniform deposit impactor) were used to measure the number and mass distributions of generated particles. Significant differences in specific number and mass concentration or distributions were found among different methods and nano-powders with the most specific number and mass concentration and the smallest particles being generated by the most energetic SSPD, followed by VS and RD. Near uni-modal number or mass distributions were observed for the SSPD while bi-modal number or mass distributions existed for nano-powders except nano-SiO which also exhibited bimodal mass distributions. The 30-min average results showed that the mass median aerodynamic diameter (MMAD) and number median diameter (NMD) of the SSPD ranged 1.1-2.1 μm and 166-261 nm, respectively, for all three nano-powders, which were smaller than those of the VS (MMAD: 3.3-6.0 μm and NMD: 156-462 nm), and the RD (MMAD: 5.2-11.2 μm and NMD: 198-479 nm). For nano-particles (electric mobility diameter < 100 nm), specific mass concentrations were nearly negligible for all three nano-powders and test methods. Specific number concentrations of nano-particles were low for the RD tester but were elevated when more energetic VS and SSPD testers were used. The quantitative size and concentration data obtained in this study is useful to elucidate the field emission and personal exposure data in the future provided that particle loss in the generation system is carefully assessed. [ABSTRACT FROM AUTHOR]

In this study, nanoparticle (NP, diameter < 100 nm) and respirable particles measurements were conducted at three different nanopowder workplaces, including the mixing area of a nano-SiO-epoxy molding compound plant (primary diameter: 15 nm), bagging areas of a nano-carbon black (nano-CB) (primary diameter: 32 nm) and a nano-CaCO (primary diameter: 94 nm) manufacturing plant. Chemical analysis of respirable particle mass (RPM) and NPs was performed to quantify the content of manufactured nanoparticles in the collected samples. Nanopowder products obtained from the plants were used in the laboratory dustiness testing using a rotating drum tester to obtain particle mass and number distributions. The obtained laboratory data were then used to elucidate the field data. Both field and laboratory data showed that NP number and mass concentrations of manufactured materials were close to the background level. Number concentration was elevated only for particles with the electrical mobility diameter >100 nm during bagging or feeding processes, unless there were combustion-related incidental sources existed. Large fraction of nanomaterials was found in the RPM due to agglomeration of nanomaterials or attachment of nanomaterials to the larger particles. From this study, it is concluded that RPM concentration measurements are necessary for the exposure assessment of nanoparticles in workplaces. [ABSTRACT FROM AUTHOR]

This study characterized the process by-product particles (mostly nanoparticles) released during the preventive maintenance of semiconductor fabrication facilities, such as chemical mechanical planarization (CMP), plasma-enhanced chemical vapor deposition (PECVD), and ion implantation. Manual sampling and real-time measurements with direct reading instruments were conducted to assess the exposure levels of nanoparticles and their physical and chemical properties. Significant amount of nanoparticles were observed in the breathing zone of the workers during the maintenance of the PECVD and ion implanters with the peak number concentrations as high as 6,470,000 and 65,444 #/cm3, respectively, indicating that the deposited residual chemicals in the reaction chambers were released as airborne nanoparticles by the maintenance activities. In contrast, nanoparticles released during the maintenance of the local scrubber, CMP, and replacing CMP slurry drums were insignificant. Causes of the particle release were discussed and suggestions were made to mitigate the nanoparticle release and reduce the exposure levels. [ABSTRACT FROM AUTHOR]