Investigation of Cut-Off Sizes and Collection Efficiencies of Portable Microbial Samplers

Abstract

Traditional collection efficiency measurements often directly compare particle concentrations upstream and downstream of the sampler without considering the particle losses. Here, we developed a new approach which tests collection efficiencies of the sampler with and without agar collection plate loaded. This method thus allows estimating the effective collection efficiency, i.e., the fraction of incoming particles deposited onto the agar collection medium only.The experimental cut-off sizes, or d 50 , of the investigated samplers ranged from 1.2 µm for the RCS High Flow, 1.7 µm for the MAS-100, 2.1 µm for SAS Super 180, to 2.3 µm for MAT; for other three samplers they were close to or above 5 µm. In most cases the theoretical d 50 was lower than the experimental value, which was likely due to the dissipation of impactor jets and the influence of cross-flow in the multi-nozzle impactors. For most samplers, we observed a notable difference between the collection efficiency obtained by the traditional measurement method and the effective collection efficiency. In general, all samplers collected 10% or less of 0.5 µm particles onto the agar medium.This study indicates that the use of most of the tested bioaerosol samplers may result in a substantial underestimation of bacterial concentrations, especially of single bacterial cells with diameter 0.5-1.0 µm. On the other hand, most of the investigated samplers would be more efficient when collecting larger fungal spores.

Physical performances and kinetics of evaporation of the CIP 10-M personal sampler's rotating cup containing aqueous or viscous collection fluid

“…The shape of the collection efficiency curve and the value of the 50% efficiency diameter (d ae,50 D 2.1 mm) were quite comparable to the collection efficiencies measured for high-flow rate portable microbial samplers such as the Microbiological Air Sampler (MAS-100, 100 L/min), Surface-Air-Sampler (SAS Super 180, 180 L/min), or Millipore Air Tester (140 L/min), as measured by Yao and Mainelis (2006). Like single-stage impactors, the CIP 10-M can also be considered to be an inertial particle separator (with a rotating cup rather than an impaction plate or a Petri dish).…”

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

“…The particle collection efficiency was found to be influenced by the cross flow (Fang et al 1991) and nozzle arrangement (Kwon et al 2002). Moreover, the effect of the S/W ratio on the cutoff characteristics of the multinozzle impactors (i.e., micro-orifice impactors) has been studied (Gudmundsson et al 1995;Kwon et al 2002;Yao and Mainelis 2006). In Gudmundsson et al (1995), when S/W > 1:8, (Stk 50 ) 1/2 increased with an increasing S/W but decreased with an increasing Re at a fixed porosity (Po) which is defined as the total cross-sectional area of nozzles divided by the area of nozzle plate.…”

“…Increasing the S/W ratio from 1.75 to 2.25 was shown to decrease particle collection efficiency by more than 10%. Yao and Mainelis (2006) investigated the effect of the S/W ratio on the physical collection efficiency of the multinozzle bioaerosol impactors. Results showed that the d pa50 decreased when the S/W ratio was decreased over the range from 2.7 to 9.…”

Effect of Agar Plate Volume on Accuracy of Culturable Bioaerosol Impactors

“…While staying within the recommended S/W range of about one to five (Marple and Olson 2011), Yao and Mainelis (2006a) have demonstrated improved physical collection efficiency in multinozzle portable agar impactors by increasing agar plate volume and thus decreasing S/W. However, in addition to physical collection of particles, biological collection efficiency also needs to be considered when collecting culturable samples with different agar volumes.…”