Design and Testing of the NCTU Micro-Orifice Cascade Impactor (NMCI) for the Measurement of Nanoparticle Size Distributions

Abstract

The NCTU micro-orifice cascade impactor (NMCI) was redesigned and tested to enable the measurement and adjustment of the jet-to-plate distance (S) of the impactors by using a micrometer. Each stage of the NMCI contains an impaction plate and a nozzle plate which are separated. The bottom casing for impaction plate assembly and the nozzle plate holder of each stage are separated. Calibration results show that the cutoff aerodynamic diameter (d pa50 ) of the three lower stages (d pa50 D 180, 100, and 56 nm) are close to the nominal values given in Marple et al. (1991). In addition, the S/W (W: nozzle diameter) effects on the d pa50 for the three lower stages were investigated and an empirical equation was developed to facilitate the prediction of d pa50 when the nozzle diameters may change slightly from one batch to another. The relationship between the nozzle diameter and pressure drop of the micro-orifice impactors at the fixed operational flow rate of 30 L/min was also established so that the nozzle diameters can be predicted from the pressure drop measurement. An empirical equation was proposed to express the correlation between the dimensionless cutoff size and the S/W ratio when considering isentropic flow to facilitate the design of microorifice impactors for S/W > 4. It is expected that the present NMCI could improve the accuracy of size classification of submicron particles below 180 nm, especially for nanoparticles.

Influence of the Dilution System and Electrical Low Pressure Impactor Performance on Particulate Emission Measurements from a Medium-scale Biomass Boiler

“…Because the ELPI+ contains an additional impactor stage and an electrical filter stage (Järvinen et al, 2014), this would correspond with more particles expected in Stages 8-10 and less in Stages 5-7 as a bias from long-term collection with the ELPI+. Impactors have been designed and developed that can reduce and even eliminate the effects of particle overloading (Tsai and Cheng, 1995;Peters et al, 2001;Tsai et al, 2012;Chien et al, 2015;Le and Tsai, 2017;Le et al, 2019), but these are not suitable for implementation in the ELPI+. It should however be noted that the effects of overloading the ELPI+ impactor can be largely postponed by using oil-soaked sintered impactor plates instead of greased impactor plates (van Gulijk et al, 2003).…”

Characterization of Atmospheric PM2.5 Inorganic Aerosols Using the Semi-Continuous PPWD-PILS-IC System and the ISORROPIA-II

“…In comparison, the predicted values of Cl − are comparable with the observations (slope = 0.74) but data are scattered at low concentrations (648/720 data < 1 µg/m 3 ) resulting in a moderate correlation with R 2 of 0.49. The distributions of the WSI ions at this sampling site were tested for five days from July 2016 to January 2018 using the NCTU micro-orifice cascade impactor (NMCI) [62,63]. The results, shown in Figure S1 in SI, indicated that Cl − was mainly formed in coarse particles (PM 10-2.5 ) which were not measured in this study, resulting in the underestimation of the model for Cl − and the overestimation for HCl ( Figure S2 in SI).…”

Inertial Impaction Technique for the Classification of Particulate Matters and Nanoparticles: A Review

“…We found the inter-stage loss of NP clogging in the last four stages of the micro-orifice uniform deposit impactor (MOUDI) due to its step-wised nozzle structure with abrupt contraction (Liu C.N. et al, 2013b) and developed the NCTU micro-orifice cascade impactor (NMCI) with smooth nozzle shape to eliminate these problems (Chien C.L. et al, 2015).…”