Browsing by Author "Le, Thi-Cuc"

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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
;
Wang, Yun-Chin
;
Pui, David Y. H.
;
Tsai, Chuen-Jinn
;
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.
Novel non-bouncing PM2.5 impactor modified from well impactor ninety-six
(2017-01-01)
Le, Thi-Cuc
;
Tsai, Chuen-Jinn
;
環境工程研究所
;
Institute of Environmental Engineering
The impaction well containing an oil-soaked glass fiber (GF) filter of the well impactor ninety-six (WINS) needs to be replaced every five sampling days to avoid particle overloading which affects the cutoff diameter (d(pa50)) and the sampling accuracy. This study developed a novel modified WINS (M-WINS) which uses water to wash the wetted GF filter substrate clean continuously to eliminate the particle overloading effect and extend the service life of the impactor without the need of impaction well cleaning and replacement of the oil-soaked GF filter. The laboratory test showed that d(pa50) of the M-WINS only varied slightly from 2.44 to 2.49 mu m while d(pa50) of the WINS decreased from 2.44 to 2.05 mu m when the loaded particle mass increased from 0-6 mg. The field test showed that d(pa50) and the sampling bias of the novel M-WINS met the USEPA requirements (d(pa50) = 2.5 +/- 0.2 mu m and sampling bias +/- 5%) while the WINS without regular replacement of the well showed the decrease in d(pa50) down to 2.12 mu m and the increase in the negative sampling bias to -20% after 17 continuous sampling days. Therefore, the current M-WINS can be used as the PM2.5 inlet for unattended, continuous sampling for a long time with a very good sampling accuracy.
On the concentration differences between PM2.5 FEM monitors and FRM samplers
(2020-02-01)
Le, Thi-Cuc
;
Shukla, Krishna Kumar
;
Chen, Yu-Ting
;
Chang, Shun-Chin
;
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.
The Predictive Method for the Submicron and Nano-Sized Particle Collection Efficiency of Multipoint-to-Plane Electrostatic Precipitators
(2013-10-01)
Le, Thi-Cuc
;
Lin, Guan-Yu
;
Tsai, Chuen-Jinn
;
環境工程研究所
;
Institute of Environmental Engineering
The multipoint-to-plane electrostatic precipitator (ESP) is one type of ESP devices used for the sampling and control of nanoparticles and sub-micron particles, with the advantage of a low pressure drop and high particle collection efficiency. Several empirical equations for predicting the particle collection efficiency are available in the literature, but most of them are only applicable to wire-in-plate ESPs. For ESPs with different discharge electrodes, the empirical equations are different since the ion concentration and electric fields are different. In this paper, a predictive method is developed to calculate the particle migration velocity and the particle collection efficiency equation eta(%) of multipoint-to-plane ESPs in the form of eta(%) = {1 - exp{-[beta(1)(N-De(beta 2)) + beta(3)(N-De) + beta(4)]}} x 100%, in which beta(1), beta(2), beta(3) and beta(4) are regression coefficients and N-De is the Deutsch number determined by the particle migration velocity. Good agreement is obtained between the present model predictions and the experimental particle collection efficiencies obtained from the literature. It is expected that the present model can be used to facilitate the design of efficient multipoint-to-plane ESPs for nanoparticle and sub-micron particles removal in the future.