Aerosol-to-hydrosol transfer stages for use in bioaerosol sampling

Abstract

Single-jet and multijet aerosol-to-hydrosol transfer stages (AHTSs) with cutpoints of 2 and 0.8 μm aerodynamic diameter, respectively, were designed and evaluated. The devices are intended to take the coarse particle flow stream (minor flow) from a virtual impactor and concentrate the aerosol particles into a low flow rate of liquid. The design air flow rate for each system is 1 L/min, and the collection liquid flow needs to be ≥0.3 mL/min with a surfactant added to prevent loss of hydrosol particles on internal surfaces of the devices. Satisfactory performance was achieved when distilled water with 0.1% Tween 20 was used as the collection fluid. The effectiveness (average fractional efficiency) for the single-jet device is 94% over the size range of 2.5 to 10 μm aerodynamic diameter, and that of the multijet AHTSs is 90% over the size range of 1 to 10 μm aerodynamic diameter. The systems have an ideal air power consumption of 1.4 mW and 4.5 mW, respectively. If an AHTS were operated in a heated enclosure and sampled air at -28°C, less than 1 W of heating would be required to prevent freezing. Preliminary results of bioaerosol testing with 0.7 μm AD single spores of Bacillus globigii var. niger show efficiencies over 100%. These values are probably due to the different expression of viability of the spores in the reference samples and those in the output liquid of the AHTSs.