Browsing by Author "Shukla, Krishna Kumar"

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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.
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