Browsing by Author "Yeh, Huajun"

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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
;
Liu, Yingshu
;
Lin, Yujie
;
Gautam, Sneha
;
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.
Sampling efficiency of low-volume PM10 inlets with different impaction substrates
(2019-03-04)
Thi-Cuc Le
;
Shukla, Krishna Kumar
;
Sung, Jung-Che
;
Li, Ziyi
;
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