Browsing by Author "Li, Ziyi"

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A mass correction method for the aerosol particle mass analyzer to measure the particle mass of sub-50 nm nanoparticles
(1970-01-01)
Liao, Bo-Xi
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Gong, Wen-Cheng
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Li, Ziyi
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Tsai, Chuen-Jinn
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環境工程研究所
The particle mass measurement instrument of the aerosol particle mass analyzer (APM) tends to underestimate the particle mass of sub-50 nm nanoparticles, limiting the APM mass measurement to larger particles. In the present work, a mass correction method was developed based on a calibration reference to correct the APM mass underestimation according to a measured mass-based dimensionless parameter The correction was tested using laboratory generated silver nanoparticles and ambient nanoparticles. It was found that the measured effective density variations of silver nanoparticles due to different extent of APM mass underestimation at different operating conditions were reduced by the correction method with a significant improvement of R-squared from 0.40 to 0.87. In addition, about 20% increase in the effective density from 0.91 to 1.09 g/cm(3) was observed for 30 nm ambient wet nanoparticles using the correction method. The difference between the raw and corrected effective densities is due to the mass underestimation by the APM itself, which should be corrected in the data analysis program of the APM. Copyright (c) 2019 American Association for Aerosol Research
A numerical modelling study of SO2 adsorption on activated carbons with new rate equations
(2018-12-01)
Li, Ziyi
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Liu, Yingshu
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Wang, Haihong
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Tsai, Chuen-Jinn
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Yang, Xiong
Modelling dynamic adsorption of sulfur dioxide (SO2) on activated carbons (ACs) is significant in guiding practical desulphurization processes and making highly efficient use of adsorbents in terms of the adsorption rate which largely depends on particle size. In this work, models derived from the Vermeulen and an improved linear driving force (LDF) rate equation were studied for the first time on SO2 adsorption over AC particles with different sizes. For larger particles (>= 3 mm), breakthrough curves predicted by the Vermeulen equation showed good agreement with experimental data, demonstrating that intraparticle diffusion resistance varied with particle size, feed concentration, adsorption time and location. For smaller particles (1 mm), a correction on the volume-averaged adsorption capacity as a function of adsorption time and saturation in the rate equation was developed to avoid the underestimation of adsorption rate due to the inappropriate parabolic concentration profile inherent in the conventional LDF model. By providing a concentration gradient and adsorption rate closer to actual values, the improved LDF equation was confirmed to provide excellent prediction results on 1-mm particles. Different modelling characteristics of the two models indicates varying effects of intraparticle diffusion on adsorption rate with particle size regarding the specificity of SO2 physisorption on ACs.
Adsorption phenomena and related mechanisms of airborne nanoparticles on porous materials
(2018-08-19)
Li, Ziyi
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Liu, Yingshu
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Tsai, Chuen-Jinn
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Xing, Yi
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Lu, Pei
Desorption of Polycyclic Aromatic Hydrocarbons on Mesoporous Sorbents: Thermogravimetric Experiments and Kinetics Study
(2016-02-10)
Li, Ziyi
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Liu, Yingshu
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Yang, Xiong
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Xing, Yi
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Tsa, Chuenjinn
The desorption performances of naphthalene and pyrene on mesoporous MCM-41, SBA-15, and CMK-3 sorbents are studied on the basis of temperature-programmed desorption experiments over the temperature range of 350-800 K at different heating rates. The kinetic parameters for each sorbate sorbent pair are determined with combined model-fitting methods. The data for naphthalene and pyrene are best fitted with the same kinetic models on MCM-41 (with 1D mesopore channels), in contrast to those on SBA-15 and CMK-3, which have micropore mesopore structures, leading to different desorption mechanisms for these two sorbates. SBA-15 with interconnectivity between adjacent mesopores not only shows high sorption capacities but also offers diffusion advantages in desorption, which contributes to the order of the degree of ease in desorption: SBA-15 > MCM-41 > CMK-3. CMK-3, with higher microporosity and hydrophobicity, shows stronger binding with the adsorbates while still benefiting in pyrene desorption from the consecutive mesoporosity.
Development of a Novel Shallow Liquid Interface Exposure System for MWCNT Toxicity Assessment
(2019-10-01)
Tien, Chi-Yu
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Li, Jui-Ping
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Han, Ding
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Li, Ziyi
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Fu, Pin-Kuei
Increasing applications of multiwalled carbon nanotubes (MWCNT) lead to significant occupational exposure and potential health concerns. Toxicity of MWCNT should be carefully elucidated since the conventional (CON) method with fully immersed condition fails to mimic the air-liquid interface (ALI) in airways. Additionally, quantification of MWCNT in cells was a real challenge. Currently available ALI exposure devices are costly, posing problems to conducting in vitro evaluations for emerging nanomaterials. A novel system, consisting of a shaker fluidized-bed atomizer (SFA) and electrostatic shallow liquid interface (ESLI) exposure chamber, has been developed for investigating nanotoxicity of well-dispersed pristine-MWCNT (pMWCNT) and carboxylized-MWCNT (cMWCNT). After 24-h exposure, LDH, MCP-1, IL-1 beta, IL-6, and TNF-alpha releases were determined, and cell uptakes were quantified according to the molybdenum content in cells. Biological responses triggered by SLI exposure are obviously more sensitive compared with those caused by CON exposure at equivalent doses. Exposure dose-dependent release of LDH and IL-6 was highlighted in A549 cells, indicating higher cytotoxicity and inflammatory responses of cMWCNT attributed to its shorter length, smaller size, and higher cell uptake. Cell-associated dose-dependent release of LDH and IL-6 was highlighted in RAW264.7 cells, revealing the higher adverse health risk of pMWCNT due to frustrated phagocytosis and its much higher molybdenum content. These results suggest that inherent characteristics of cells and distinct physicochemical properties of pMWCNT and cMWCNT lead to either exposure dose-dependent or cell-associated dose-dependent responses. Notably, the SLI is superior to the CON exposure method and well suited for nanotoxicity assessment of different MWCNTs.
Development of an Automated System (PPWD/PILS) for Studying PM2.5 Water-Soluble Ions and Precursor Gases: Field Measurements in Two Cities, Taiwan
(2017-02-01)
Li, Ziyi
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Liu, Yingshu
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Lin, Yujie
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Gautam, Sneha
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Kuo, Hui-Chuan
An automated system consisting of a particle-into-liquid sampler (PILS) and a parallel plate wet denuder (PPWD) coupled with an ion chromatography was used for simultaneous measurement of ambient water-soluble ions in PM2.5 and precursor gases. The performance of the PPWD/PILS was validated by comparing it with the PDS (porous metal denuder sampler) for precursor gases (NH3, HONO, HNO3 and SO2) and PM2.5 ionic species (NH4+, NO3-, SO42-, Na+, Cl- and K+) measured in Taipei and Hsinchu Cities of Taiwan. Good correlations were demonstrated with linear regression slopes ranging from 0.92 to 1.04 and 0.84 to 0.97 as well as R-2 ranging from 0.76 to 0.83 and 0.89 to 0.94, for precursor gases and PM2.5 ions, respectively. The accuracy of the current system for precursor gases outperforms the other commercial systems. Field continuous data showed that NH3 was the most abundant precursor gas with the diurnal pattern peaking at low nocturnal boundary heights and during rush hours with local traffic emissions in Taipei, and with the pattern peaking only at mid-day associated with regional sources in Hsinchu. A reverse diurnal pattern for HONO in Taipei reflected the daytime photolysis and its nocturnal heterogeneous reaction, while its concentration was relatively constant at very low level in Hsinchu. SO42-, NH4+ and NO3- exhibited very similar diurnal patterns with the mean concentrations of 4.56 +/- 3.14, 1.55 +/- 1.16 and 0.52 +/- 0.5 mu g m(-3) in Taipei, and 7.95 +/- 5.52, 2.41 +/- 1.95 and 0.96 +/- 1.10 mu g m(-3) in Hsinchu, respectively. Correspondingly high concentrations of major ions to precursor gases were associated with the photochemical secondary aerosol formations and heavy traffic in Taipei. Based on an ammonia-rich atmosphere and high SOR values, (NH4)(2)SO4 and NH4NO3 were inferred to be the dominant inorganic salts in PM2.5 at both sites, which were also verified by the ion balance analysis.
Experimental and theoretical analysis of loading characteristics of different electret media with various properties toward the design of ideal depth filtration for nanoparticles and fine particles
(2020-02-15)
Tien, Chi-Yu
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Chen, Jiang-Ping
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Li, Shihang
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Li, Ziyi
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Zheng, Yu-Ming
Loading experiments of four electret fibrous media having various properties, including fiber diameter, porosity, thickness, charging density and fibrous structure, with fine and nanosized particles were conducted for finding out the influencing factors on efficiency decline and particle holding capacity. The four media include a commercial HVAC media rated with the minimum efficiency reporting value of 13 (MERV13), and three home-made media, including a coarse fiber (CF) layer, a melt-blown (MB) layer, and a bead-on-string (BS) layer. A theoretical model for predicting the pressure drop growth along the loading was applied and compared with that of experiments. The experimental results revealed that the charges of electret media did enhance the holding capacity. The decline of efficiency was found to closely relate to the holding capacity of each media. Higher capacity resulted in a higher decline of efficiency. The theoretical calculation illustrated that the ideal holding capacity was significantly higher than the current electret media had achieved, which indicates that it leaves much improvement of media design more desirable. Comparing the theoretical and experimental results of pressure drop growth with respect to mass load, it was found the current electret layers performed different levels of ideal depth filtration, with an order of CF > MERV13 > BS > MB. Beyond the ideal filtration, pressure drop growth raised exponentially. By utilizing their individual ideal filtration stage, three composite media consisting of 3-4 layers of these electrets with a total thickness less than 1 mm were combined and tested. At 1 in-H2O of pressure drop, the composite electret CF + MERV13 + BS achieved the highest holding capacity with 14.1 g m(-2) which was at least 5-10 times higher than the existing commercial HEPA filters. The bead-onstring fibrous structure of BS enhanced the holding capacity of the composite media significantly. The newly developed electret-based composite filters performed an energy efficient filtration for fine and nanosized particles.
Experimental research on purifying ultrafine nanoparticle by SBA-15 and its filtration mechanism
(2018-05-01)
Xing, Yi
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Yu, Han
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Lu, Pei
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Li, Ziyi
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Liu, Yingshu
Airborne ultrafine nanoparticle (UFNP) is a key factor causing heavy haze pollution in Beijing-Tianjin-Hebei, which is very harmful to human health and the environment. Removal of environmental UFNPs by porous material is an important method of air purification treatment. However, the specific mechanism by which porous material filters UFNPs is not clear. In this study, UFNPs with 2-10 nm diameter were removed by SBA-15 mesoporous silica molecular sieves with different pore sizes, and the filtration mechanism was analyzed using transmission electron microscopy (TEM), specific surface area tests (BET), and X-ray photoelectron spectroscopy (XPS). The analyses showed a distinctive filtration of UFNPs over the interior mesopore channels. The removal efficiencies of SBA-15 with different pore sizes were also compared, demonstrating the influence of the pore size and structure on most penetrating particle size (MPPS). The UFNP filtration efficiency of SBA-15 increased with the increase of pore size. Moreover, SBA-15-14.6 could effectively purify UFNPs, and it had the highest fractional diffusive filtration efficiency of 98.79% and a total efficiency of 92.58% for UFNPs. This study provides a technical basis for the filtration of UFNPs using mesoporous materials. (C) 2018 Elsevier B.V. All rights reserved.
Exposure assessment of process by-product nanoparticles released during the preventive maintenance of semiconductor fabrication facilities
(2018-07-20)
Liao, Bo-Xi
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Tseng, Neng-Chun
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Li, Ziyi
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Liu, Yingshu
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Chen, Jen-Kun
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 #/cm(3), 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.
Getting insight into the influence of coexisting airborne nanoparticles on gas adsorption performance over porous materials
(2020-03-15)
Xing, Yi
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Cui, Yongkang
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Li, Ziyi
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Liu, Yingshu
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Bao, Danqi
Adsorption as one of the most important air cleaning methods has been extensively applied during which the coexisting airborne nanoparticles (NPs) with sizes close to adsorbent pore sizes could inevitably influence gas adsorption processes. In this work, the influence of sub-20 nm NPs on toluene adsorption on ZSM-5 zeolites exchanged with different cations (Li+, Na+ and K+) were studied based on gas-and-particle coexisting adsorption/filtration tests. Affinities for both toluene and NPs on adsorbents follow Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5 regarding the orders of charge density, pore size, and internal and external specific surface areas. The toluene adsorption was shown to be impaired by coexisting NPs from perspectives of thermodynamics and kinetics. For Li-ZSM-5, Na-ZSM-5 and K-ZSM-5, significant relative reductions of 10.4 %, 10.5 % and 16.0 % in toluene adsorption capacity at the lower feed concentration, and of 20.3 %, 15.2 % and 2.3 % in mass transfer coefficient at the higher feed concentration were observed, respectively. The influential mechanisms regarding competitiveness between toluene and NPs in interaction with cationic and porous surfaces were accordingly proposed, which are of practical significance for selecting robust adsorbents under realistic harsh air conditions.
Novel Wire-on-Plate Electrostatic Precipitator (WOP-EP) for Controlling Fine Particle and Nanoparticle Pollution
(2015-07-21)
Li, Ziyi
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Liu, Yingshu
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Xing, Yi
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Thi-Minh-Phuong Tran
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Thi-Cuc Le
A new wire-on-plate electrostatic precipitator (WOP-EP), where discharge wires are attached directly on the surface of a dielectric plate, was developed to ease the installation of the wires, minimize particle deposition on the wires, and lower ozone emission while maintaining a high particle collection efficiency. For a lab-scale WOP-EP (width, 50 mm; height, 20 mm; length, 180 mm) tested at the applied voltage Of 18 kV, experimental total particle collection efficiencies were found as high as 90.9-99.7 and 98.8-99.9% in the particle size range of 30-1870 nm at the average air velocities of 0.50 m/s (flow rate, 30 L/min; residence time, 0.36 s) and 0.25 m/s (flow rate, 15 L/min; residence time, 0.72 s), respectively. Particle collection efficiencies calculated by numerical models agreed well with the experimental results. The comparison to the traditional wire-in-plate EP showed that, at the same applied voltage, the current WOP-EP emitted 1-2 orders of magnitude lower ozone concentration, had cleaner discharge wires after heavy particle loading in the EP, and recovered high particle collection efficiency after the grounded collection plate was cleaned. It is expected that the current WOP-EP can be scaled up as an efficient air-cleaning device to control fine particle and nanopartide pollution.
On the concentration differences between PM2.5 FEM monitors and FRM samplers
(2020-02-01)
Le, Thi-Cuc
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Shukla, Krishna Kumar
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Chen, Yu-Ting
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Chang, Shun-Chin
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Lin, Tsai-Yin
BAM-1020 and TEOM-FDMS have undergone rigorous testing and analysis protocols to become the Federal Equivalent Method (FEM) monitors and serve as reliable near real-time monitors for compliance with the National Ambient Air Quality Standards and references for low-cost PM2.5 sensor calibration. However, differences between the FEM and FRM (Federal Reference Method) data still exist, which cause inconsistency in PM2.5 measurements. This study carried out the field tests across five geographically diverse stations in different seasons in Taiwan with 265 daily samples collected by the collocated BAM-1020 and TEOM-FDMS and the FRM sampler and found that the biases between the FEM and FRM values increased with the decreasing PM2.5 concentrations and varied with ambient conditions. The measurement uncertainties exist in the BAM-1020 were mainly due to the aerosol water content, while the TEOM-FDMS always over-measured PM2.5 compared to the FRM sampler since it corrects for the evaporation loss of semi-volatile particle materials. To reduce the biases between the FEM monitors and FRM samplers, empirical equations based on PM2.5 concentrations (mu g m(-3)), temperature (degrees C), and relative humidity (%) were derived to convert the FEM data to the FRM data. After correction, the mean normalized biases were decreased from +1.67 +/- 12.43% to +0.63 +/- 8.75% for the BAM1020 and from +13.86 +/- 14.50% to 0.85 +/- 9.0% for the TEOM-FDMS. Also, the same empirical equation was used to convert the FRM PM2.5 values to the "true" or "actual" PM2.5 values represented by the TEOM-FDMS with the bias reduced from -10.76 +/- 11.42% to +1.33 +/- 8.44% after conversion.
Performance of mesoporous silicas (MCM-41 and SBA-15) and carbon (CMK-3) in the removal of gas-phase naphthalene: adsorption capacity, rate and regenerability
(2016-01-01)
Liu, Yingshu
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Li, Ziyi
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Yang, Xiong
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Xing, Yi
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Tsai, Chuenjinn
The adsorption isotherms of naphthalene on three typical mesoporous adsorbents, mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3 were determined by column tests at 125 degrees C, with feed concentrations ranging from 7.63 x 10(-5) to 4.64 x 10(-2) mol m(-3) (1.88 to 1140 ppm). The Langmuir model and constant-pattern wave propagation model were found to well fit the isotherms and the breakthrough curves, respectively. Regenerabilities of the mesoporous samples and a benchmark activated carbon (AC) were characterized based on thermogravimetric analysis (TGA). The results show mesoporosity significantly reduced the internal mass-transfer resistance, contributing to facile desorption and to fast adsorption kinetics shown by high overall mass-transfer rate coefficient following the order of: CMK-3 > SBA-15 > MCM-41. Micropore-mesopore coexisting structures present in CMK-3 and SBA-15 facilitated the adsorption at very low concentrations due to micropore-filling, while greater surface hydrophobicity and micropore abundance on CMK-3 exhibited larger affinity for nonpolar naphthalene, rendering the highest adsorption capacity (1.014 mol m(-3)) among all sorbents including ACs. SBA-15 showed higher regenerability with a desorption temperature below 440 K, owing to the weaker binding and diffusion advantages contributed by the interconnectivity between primary mesopores.
Performance of mesoporous silicas and carbon in adsorptive removal of phenanthrene as a typical gaseous polycyclic aromatic hydrocarbon
(2017-02)
Li, Ziyi
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Liu, Yingshu
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Yang, Xiong
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Xing, Yi
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Tsai, Chuen-Jinn
Adsorptive removal of the predominant polycyclic aromatic hydrocarbons (PAHs), represented by phenanthrene, from hot gases using mesoporous adsorbents (mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3) has been studied through tests of column adsorption and temperature programmed desorption (TPD). Adsorption equilibria on MCM-41 and CMK-3, and on SBA-15 were well described by Langmuir and Freundlich models, respectively, showing the order of adsorption capacity of CMK-3 > SBA-15 > MCM-41 originated from different geometrical structures and texture properties. Adsorption dynamics based on breakthrough fitting by the constant-pattern wave propagation model showed that mesoporosity contributed to fast overall adsorption kinetics by reducing the internal resistance as being the predominant mass-transfer step, particularly on SBA-15 with a 2-D cross-linked structure. The TPD tests revealed the order of ease of desorption of SBA-15 approximate to MCM-41 > CMK-3, where the structural advantage on SBA-15 dominated the strong site binding as indicated by the intrinsic activation energy and exponential factor obtained by TPD models. Results from different TPD models showed that re-adsorption effect during desorption increased with decreasing dimension of adsorbent structure and that the utilization of the simplified linear TPD model could be violated by the strong sorbate-sorbent binding. Comparisons with traditional adsorbents and with the removal of naphthalene by these mesoporous adsorbents were made, showing higher applicability of CMK-3 for phenanthrene regarding stronger adsorption affinity and capacity as well as decreased disadvantages in regenerability relative to mesosilicas. (C) 2016 Elsevier Inc. All rights reserved.
Removal of ultrafine particles by porous nanomaterials with varied morphologies
(2019-01-15)
Yin, Likun
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Yang, Xiong
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Xing, Yi
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Lu, Pei
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Tsai, Chuen-Jinn
The removal characteristics of sub-25 nm ultrafine particles (UFPs) by different porous nanomaterials with different morphologies were studied based on efficiency curves obtained with specially designed filtration system. The material morphological effects on UFPs collection were investigated. The results demonstrate a complex and synergic mechanism of material structural framework, pore size distribution, and porosity order in terms of diffusion and interception dependent on flow velocity. Both porosity and fiber-like tubular structures promoted the UFPs removal. Microporosity and disordered mesoporosity could enhance the roughness of the internal surface and intensify the interaction with UFPs. Specifically, the large and ordered mesoporosity was able to render selectivity for UFPs at certain sizes and exhibited the best particle collection performance which can be largely associated with significant pore size and volume. The dependence of the ratio of diffusion to interception on flow velocity and the comparison of different pores in terms of the matching sizes with particles derived from single sphere efficiency model fitting results were also discussed. This work is significant to deeper understanding of interactions between airborne nanoparticles and porous surfaces. (C) 2018 Published by Elsevier B.V.
Research Progress of Gaseous Polycyclic Aromatic Hydrocarbons Purification by Adsorption
(2019-04-01)
Yang, Xiong
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Li, Ziyi
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Liu, Yingshu
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Xing, Yi
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Wei, Jinchao
Gaseous polycyclic aromatic hydrocarbons (PAHs) are carcinogenic and mutagenic pollutants and also able to promote the growth of secondary particulate matters, which have attracted great attention in recent years. Control of PAHs emissions in exhaust gases using different techniques has been hot topics in the atmospheric environment field. Adsorption is one of the most effective ones and is well accepted by industries in gaseous pollutant removal in which the adsorbent characteristics play critical roles. In this paper, the latest advances in the field of PAHs adsorption are critically reviewed with special emphasis on adsorption-desorption characteristics and related applications. Studies on adsorption equilibrium, kinetics, and desorption properties of PAHs as special low-volatile gases on conventional activated carbons and novel mesoporous adsorbents are summarized and compared, showing the advantages of mesoporous adsorbents over traditional adsorbents in terms of the fast adsorption and facile desorption. The significant factors on the optimal balance between adsorption and desorption as well as the corresponding adsorbent materials are discussed in detail. This work can be a reference for further studies on adsorptive purifications of PAHs and other low-volatile gases.
Sampling efficiency of low-volume PM10 inlets with different impaction substrates
(2019-03-04)
Thi-Cuc Le
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Shukla, Krishna Kumar
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Sung, Jung-Che
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Li, Ziyi
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Yeh, Huajun
The louvered 16.7 L min(-1) PM10 inlet is commonly used in PM10 and PM2.5 FRM samplers or FEM monitors. Its sampling efficiency is influenced by particle bounce, re-entrainment, and overloading since the PM10 inlet contains a PM10 impactor with an uncoated impaction surface. In this study, a modified PM10 (M-PM10) inlet with an oil-soaked glass fiber filter substrate supported by an oil-soaked porous metal disc was developed to eliminate the particle bounce and overloading effects. The oiled M-PM10 inlet and the traditional PM10 inlets with and without grease coating were collocated at the field for long-term comparison tests. The results show that the traditional uncoated PM10 inlet which is cleaned initially but not cleaned daily afterwards oversamples PM10 concentration after one 24-h sampling day and has the high positive average sampling bias during 14 sampling days due to particle bounce and re-entrainment. The grease-coated PM10 inlet without daily cleaning shows a better performance with a smaller sampling bias, but it still oversamples PM10 concentrations after the first three 24-h sampling days and then undersamples after 10 sampling days due to particle bounce and overloading effects, respectively. In comparison, the M-PM10 inlet shows a good performance with a small average sampling bias during 35 sampling days since vacuum oil wicks up through the deposit to eliminate particle bounce and overloading. It is suggested that the oiled M-PM10 inlet can be used to replace the traditional EPA PM10 inlet and for long-term sampling of over 1 month without the frequent maintenance need. Copyright (c) 2019 American Association for Aerosol Research