Browsing by Author "Hsi, Hsing-Cheng"

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A size-segregation method for monitoring the diurnal characteristics of atmospheric black carbon size distribution at urban traffic sites
(2014-06-01)
Cheng, Yu-Hsiang
;
Liao, Chung-Wen
;
Liu, Zhen-Shu
;
Tsai, Chuen-Jinn
;
Hsi, Hsing-Cheng
Understanding the characteristics of the size distribution of ambient black carbon (BC) in distinct environments is critical because the influence of BC aerosols on climate, visibility, and human health depends strongly on the distribution of BC aerosols over the particle size spectrum. In this study, a novel method for determining the mass size distribution of BC in atmospheric aerosols was developed. This size-segregation method relies on measuring BC in parallel using two aethalometers, one of which is used to measure the total BC (BCT) mass concentration as a reference level and the other is used to measure the BC (BC;) mass concentration for BC sizes below specific particle sizes that are selected using a size cut-off inlet. In this study, this method was applied to measure BC in atmospheric samples at an urban traffic site. The aethalometers were operated continually from December 15, 2012 to January 31, 2013, and from February 15, 2013 to March 31, 2013. The measurement results presented in this paper are for the diurnal variation patterns, average concentrations, mass fractions, and size distributions of BC aerosols. The results indicate that BC T mass concentration is approximately 2.8 mu g m(-3) in the Taipei urban area. The levels of BC at this sampling site were affected markedly by traffic emission levels and local wind speed. At the sampling site, the average BC2.5/BCT; BC1.0/BCT, BC0.5/BCT, BC0.25/BCT, and BC0.1/BCT were 0.96 +/- 0.04, +/- 0.92 +/- 0.07, 0.89 +/- 0.04, 0.73 +/- 0.10, and 0.18 +/- 0.08, respectively. The results indicate that approximately 90% of the BC aerosols were smaller than 0.5 mu m, that most of the BC aerosols (55%) were in the size range of 0.1-0.25 mu m, and that approximately 18% of the BC aerosols were ultrafine. Moreover, the daily average mass size distribution of BC exhibited a single accumulation mode at 0.16 gm at this sampling site. The mode of the BC mass size distribution at rush hour (9 AM) was only 0.14 mu m, which is smaller than the daily average. Moreover, the mode of the BC mass size distribution at an early morning hour (3 AM) was 0.18 mu m, and a minor coarse mode was also observed during this period. The results further revealed that the geometric diameter (D-pg) of the BC aerosols varied between 0.14 and 0.22 mu m and the geometric standard deviation (sigma(g)) of these BC aerosols ranged between 1.4 and 2.3 during the sampling period. Because BC exhibits extremely low chemical reactivity; the size distribution of BC in the atmosphere does not change substantially except through coagulation. (c) 2014 Elsevier Ltd. All rights reserved.
Single-Step Synthesis of Al-Doped TiO2 Nanoparticles Using Non-Transferred Thermal Plasma Torch
(2012-01-01)
Tsai, Cheng-Yen
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Hsi, Hsing-Cheng
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Bai, Hsunling
;
Fan, Kuo-Shuh
;
Sun, Hung-Dar
Al-doped TiO2 nanoparticles possessing visible-light photocatalytic activity were fabricated with an atmospheric-pressure thermal plasma system via a single-step direct combination of vaporized Ti, Al, and O-2. Pure Ti and Al2O3 powders and ultrahigh-purity O-2 were used as the precursors. The experimental results showed that the size of synthesized TiO2 was between 10 and 105 nm. Nevertheless, the nanoparticles with sizes smaller than 50 nm accounted for approximately 80% of the total number. The observed size reduction appeared to be the suppression on particle growth due to the introduction of Al species into TiO2 crystal. The largest specific surface area of the Al-doped TiO2 was 44 m(2).g(-1). The anatase phase was noticeably decreased with increasing the Al2O3 addition. The absorption spectra of Al-doped TiO2 shifted from UV to visible-light region with respect to an increase in Al2O3 addition. Oxygen in the formed TiO2 was found to be in TiO2 crystal lattice and in surface hydroxyl groups. Both Ti4+ and Ti3+ existed in the formed TiO2. However, the Ti3+ amount significantly increased with increasing Al2O3 addition due to Al/Ti substitution and the resulted oxygen vacancy. (C) 2012 The Japan Society of Applied Physics
TiO(2-x) nanoparticles synthesized using He/Ar thermal plasma and their effectiveness on low-concentration mercury vapor removal
(2011-10-01)
Tsai, Cheng-Yen
;
Hsi, Hsing-Cheng
;
Bai, Hsunling
;
Fan, Kuo-Shuh
;
Chen, Chienchih
Oxygen-vacant titanium dioxide (TiO(2-x) ) nanoparticles were synthesized using thermal plasma as a heating source at various applied plasma currents and He/Ar ratios. Samples with diverse characteristics were developed and the mercury removal effectiveness was subsequently evaluated. TiO(2) nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O(2) as precursors and Ar as plasma gas. TiO(2-x) in anatase phase with a particle size at 5-10 nm was formed at the He/Ar volume ratio of 25/75. Further increasing the He/Ar ratio elevated the plasma temperature, causing the tungsten to melt, vaporize from the cathode, and then dope into the formed TiO(2) nanoparticles. The doped W appeared to inhibit the growth of nanoparticles and decrease the crystallinity of formed anatase. The effectiveness of oxygen-vacant sites on Hg(0) removal under the visible light circumstance was confirmed. Hg(0) removal by the TiO(2-x) nanoparticles was enhanced by increasing the O(2) concentration. However, moisture reduced Hg(0) capture, especially when light irradiation was applied. The reduction in Hg(0) capture may be resulted from the competitive adsorption of H(2)O on the active sites of TiO(2-x) with Hg(0) and transformed Hg(2+).
TiO2-x nanoparticles synthesized using He/Ar thermal plasma and their effectiveness on low-concentration mercury vapor removal
(2011-10-01)
Tsai, Cheng-Yen
;
Hsi, Hsing-Cheng
;
Bai, Hsunling
;
Fan, Kuo-Shuh
;
Chen, Chienchih
Oxygen-vacant titanium dioxide (TiO2-x ) nanoparticles were synthesized using thermal plasma as a heating source at various applied plasma currents and He/Ar ratios. Samples with diverse characteristics were developed and the mercury removal effectiveness was subsequently evaluated. TiO2 nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O-2 as precursors and Ar as plasma gas. TiO2-x in anatase phase with a particle size at 5-10 nm was formed at the He/Ar volume ratio of 25/75. Further increasing the He/Ar ratio elevated the plasma temperature, causing the tungsten to melt, vaporize from the cathode, and then dope into the formed TiO2 nanoparticles. The doped W appeared to inhibit the growth of nanoparticles and decrease the crystallinity of formed anatase. The effectiveness of oxygen-vacant sites on Hg-0 removal under the visible light circumstance was confirmed. Hg-0 removal by the TiO2-x nanoparticles was enhanced by increasing the O-2 concentration. However, moisture reduced Hg-0 capture, especially when light irradiation was applied. The reduction in Hg-0 capture may be resulted from the competitive adsorption of H2O on the active sites of TiO2-x with Hg-0 and transformed Hg2+.