Browsing by Author "Pui, David Y. H."

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A detailed numerical study on the evolution of droplet size distribution of dibutyl phthalate in a laminar flow diffusion chamber
(2020-03-01)
Jia, Feng
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Li, Zi-Yi
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Pui, David Y. H.
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Tsai, Chuen-Jinn
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環境工程研究所
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.
Characterization of Atmospheric PM(2.5)Inorganic Aerosols Using the Semi-Continuous PPWD-PILS-IC System and the ISORROPIA-II
(2020-08-01)
Le, Thi-Cuc
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Wang, Yun-Chin
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Pui, David Y. H.
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Tsai, Chuen-Jinn
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環境工程研究所
A semi-continuous monitoring system, a parallel plate wet denuder and particle into liquid sampler coupled with ion chromatography (PPWD-PILS-IC), was used to measure the hourly precursor gases and water-soluble inorganic ions in ambient particles smaller than 2.5 mu m in diameter (PM2.5) for investigating the thermodynamic equilibrium of aerosols using the ISORROPIA-II thermodynamic equilibrium model. The 24-h average PPWD-PILS-IC data showed very good agreement with the daily data of the manual 5 L/min porous-metal denuder sampler with R(2)ranging from 0.88 to 0.98 for inorganic ions (NH4+, Na+, K+, NO3-, SO42-, and Cl-) and 0.89 to 0.98 for precursor gases (NH3, HNO3, HONO, and SO2) and slopes ranging from 0.94 to 1.17 for ions and 0.87 to 0.95 for gases, respectively. In addition, the predicted ISORROPIA-II results were in good agreement with the hourly observed data of the PPWD-PILS-IC system for SO42-(R-2= 0.99 and slope = 1.0) and NH3(R-2= 0.97 and slope = 1.02). The correlation of the predicted results and observed data was further improved for NH(4)(+)and NO(3)(-)with the slope increasing from 0.90 to 0.96 and 0.95 to 1.09, respectively when the HNO(2)and NO(2)(-)were included in the total nitrate concentration (TN = [NO3-] + [HNO3] + [HONO] + [NO2-]). The predicted HNO(3)data were comparable to the sum of the observed [HNO3] and [HONO] indicating that HONO played an important role in the thermodynamic equilibrium of ambient PM(2.5)aerosols but has not been considered in the ISORROPIA-II thermodynamic equilibrium model.
Dynamic variations of ultrafine, fine and coarse particles at the Lu-Lin background site in East Asia
(2013-10-01)
Chen, Sheng-Chieh
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Hsu, Shih-Chieh
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Tsai, Chuen-Jinn
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Chou, Charles C. -K.
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Lin, Neng-Huei
The characteristics of atmospheric ultrafine particles (i.e. <100 nm, nanoparticles or PM0.1), PM2.5 and PM10 were studied at the Lulin Atmospheric Background Station (LABS, 2862 m a.s.l., Taiwan) as part of the 7SEAS/Dongsha campaign. Sampling was conducted in July and August of 2009 and September to November of 2010, during which two 96-h and four 72-h PM samples were taken. Real-time particle size distributions were measured continuously from July to August of 2009 and July to November of 2010. PM0.1, PM2.5 and PM10 were collected by using two MOUDIs (micro-orifice uniform deposit impactor, MSP 110) and a Dichotomous PM10 sampler (Andersen SA-241) while real-time size distributions of particles of 5.5-350 nm in diameter were measured by an SMPS (scanning mobility particle sizer, TSI 3936). Filter samples were analyzed for gravimetric mass and chemical compositions, including organic carbon (OC), element carbon (EC), water-soluble ions and trace elements. Meteorology parameters and gaseous O-3 and CO concentrations were also monitored along with the SMPS data for studying particle nucleation, condensation, SOA (secondary organic aerosol) formation and long-range air pollutant transport at the LABS. SMPS data showed that nanoparticle concentrations at the LABS remained relatively stable at low level (similar to 300-500 #/cm(3)) during the nighttime (22:00-04:00), increased during daytime, and reached a maximum (similar to 2000-4000 #/cm(3)) in the afternoon (12:00-16:00). The NMD (number median diameter) showed an opposite trend with the peak number concentrations observed in the afternoon corresponding to the smallest NMD (20-40 nm). These results indicate the dominance of local sources rather than the transport from other atmospheric air because that the lifetime of nanoparticles was only few minutes. Chemical analysis of filter samples showed that the concentrations of trace elements K and Mn, which serve as biomass burning markers, were elevated in the fine particle fractions during November 9-12th when the air mass passed through South and Southeast Asia prior to reaching the LABS. The concentrations of K and Mn would have been low if the aerosols had local origins The biomass burning derived K was found in all fine particle samples at the LABS suggesting that the free troposphere around Taiwan is frequently impacted by the long-range transport of biomass burning plumes via the westerly winds. (c) 2012 Elsevier Ltd. All rights reserved.
Editorial
(2009-01-01)
Tsai, Chuen-Jinn
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Pui, David Y. H.
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環境工程研究所
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Institute of Environmental Engineering
An overview of the special issue of the Journal of Nanoparticle Research on Occupational and Environmental Health of nanotechnology is presented. Papers published in this special issue show considerable progress in understanding nanoparticle toxicity, monitoring, generation, dustiness, filtration, and applications of nanoparticles. More research is needed to ensure safe handling of nanomaterials as nanotechnology continues to develop at an incredible pace.
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.
Laboratory and field tests of a novel three-stage personal dust sampler for sampling three dust fractions simultaneously
(2008-01-01)
Tsai, Chuen-Jinn
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Chang, Cheng-Sheng
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Chen, Sheng-Chieh
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Chen, Penny
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Shih, Tung-Sheng
This study designed and calibrated a novel three-stage personal dust sampler for sampling inhalable, thoracic, and respirable dust fractions simultaneously. The sampler has an annular inlet as the first stage for inhalable dust sampling, two impactors in the second and third stages to classify thoracic and respirable dusts, respectively, and a final filter. Laboratory calibration tests using monodisperse liquid and solid particles showed that with 100 ppi (pores per inch) PUF (porous polyurethane foam) substrates and at the flow rate of 3.2 L/min, the sampling efficiency curves of both impactor stages matched with the ISO/CEN/ACGIH thoracic and respirable sampling criteria, respectively. The sampler also agreed with the inhalable criterion for particles smaller than 17 mu m while the deviation increases with increasing particle diameter with a maximum of 28% for 27 mu m particles. It was also found that collection efficiency curve for solid particles was similar to that of liquid particles, indicating that there was no solid particle bounce from the PUF substrates for both impactors. This study also compared inhalable, thoracic, and respirable dust concentrations measured by the present three-stage personal dust samplers with those of the Respicon samplers at three different workplaces. Without using a correction factor of 1.5 for the extrathoracic dusts of the Respicon, field results showed that the present three-stage sampler measured three dust fractions comparable to those of the Respicon samplers. The inhalable dust concentrations of the two samplers differed within 5% while the thoracic and respirable concentration differed by less than 22%.
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.
On the Special Issue for the 12th World Filtration Congress
(2017-11-01)
Pui, David Y. H.
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Hoeflinger, Wilhelm
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Wang, Jing
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Tsai, Chuen-Jinn
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環境工程研究所
Removal Efficiency of Bimodal PM2.5 and PM10 by Electret Respirators and Mechanical Engine Intake Filters
(2016-07)
Chen, Sheng-Chieh
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Chang, De-Qiang
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Pei, Chenxing
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Tsai, Chuen-Jinn
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Pui, David Y. H.
As China is receiving an economic boom, PM (particulate matter) pollutions not only have become a serious regional problem but also frequently impacted its neighboring counties, e.g., Korea and Japan. In addition to its adverse effects on human health, the on-and off-road engines operated in ambient can also be affected. In this study, a simple system for generating simulated ambient bimodal PMs comprising fine (PM2.5), coarse (PM2.5-10) particles was developed for evaluating the initial efficiency of seven respirator and four engine intake filters. In addition to the size fractional efficiency curves for each filter media determined from the SMPS (scanning mobility particle sizer) and APS (aerodynamic particle sizer), both number and mass based efficiency of these filters for PM2.5, PM2.5-10 and PM10 were also obtained to evaluate their performances against ambient PM pollutions. Data showed that the engine intake filters had a low efficiency for both mass and number based PM2.5, which was only about 25-30%. However, there was a large difference between their number and mass based PM10 efficiency. The former was much lower than the latter because these filters are with high efficiency only for coarse particles. Besides, the most of particles in number was resided in the fine size range while the mass was in coarse size range. For the respirator filtration tests, results showed that most of them can effectively remove both PM2.5 and PM10, in which the mass efficiency was always higher than that of number. The PM2.5 number efficiency results showed there are three out of seven respirator filters are with N-95 rated level, in which the efficiency of their most penetrating particle size is higher than 95%. The current simple experimental system could be applied to examine different purpose filters which protect human health and outdoor engines against ambient PM2.5 and PM10.
The Effect of Nanoparticle Convection-Diffusion Loss on the Transfer Function of an Aerosol Particle Mass Analyzer
(2014)
Lin, Guan-Yu
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Liao, Bo-Xi
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Tzeng, Neng-Jiun
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Chen, Chun-Wan
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Uang, Shi-Nian
The existing theoretical response spectra of APM-3600 agree well with the experimental data for submicron particles larger than 100nm in the electrical mobility diameter but not for nanoparticles. In this study, a 2-D numerical model was developed to predict the transfer function and response spectra of APM-3600 based on the detailed simulation of flow and particle concentration fields. It was found that recirculation flows existed in the annular classifying region and APM\'s inlet and outlet regions, which led to enhanced convection-diffusion loss of nanoparticles compared to that without considering flow recirculation. As a result, the APM underestimates the mass of naonoparticles due to the shift of the peak position of the transfer function to a larger diameter than the targeted diameter. The response spectra calculated with the simulated transfer function agree well both in shapes and peak values with the experimental data present in a previous study for both nanoparticles and submicron particles larger than 100 nm. The predicted particle masses also agree well with the PSL\'s experimental data of the article.Copyright 2014 American Association for Aerosol Research
The performance of the PM2.5 VSCC and oil-wetted M-WINS in long-term field sampling studies
(2020-10-15)
Thi-Cuc Le
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Fu, Chang-Xing
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Sung, Jung-Che
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Li, Zi-Yi
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Pui, David Y. H.
Most of PM2.5 FRM samplers and FEM monitors use a well impactor ninety-six (WINS) or very sharp cut cyclone (VSCC) to classify particles smaller than 2.5 mu m in diameter. However, the WINS has the particle loading effect and needs to be cleaned after 3 to 5 sampling days. The VSCC was claimed not to be affected by the particle loading effect in a laboratory study but without the support of field studies. In this field comparison study using daily cleaned VSCC as the reference, the uncleaned VSCC showed overall good performance in three long-term testing periods: period #1 (21 days), period #2 (124 days), and period #3 (30 days). However the fluctuation in PM2.5 concentrations of the uncleaned VSCC occurred in day 14 (D14) and D16 of period #1 due to particle bounce and re-entrainment effects; and also in D19, D31 and D44 of period #2, and in D28 and D29 of period #3 due to particle loading effect. After the sampling periods longer than 21 days in period #2 and #3, the particle loading effect resulted in persistently lower PM2.5 concentrations due to smaller cut-sizes and smoother penetration curves. In comparison, the oil-wetted M-WINS designed by our group showed a better performance with less than +/- 5% bias and +/- 2 mu g m(-3) concentration difference during two long-term tests: periods #2 and #3. This study proved once again that the M-WINS is a viable PM2.5 sampling inlet that meets the long-term PM2.5 sampling or monitoring need.