The hygroscopicity of airborne bio-aerosols may significantly affect their aerodynamic diameter, and thus change their aerodynamic behavior and sampling result. We have investigated the change rate in aerodynamic diameter of two different bacterial species (E.co/i, B. subti/is) and two popular aerosols (NaCl, PSL) as a function of relative humidity. Collision nebulization method was explored for the aerosolization of the aerosols.
Size-spectrometric measurements with an Aerosizer DSP (TSI, Model 3220) showed that the aerodynamic diameter of the tested bacterial aerosols does not change significantly when the relative humidity increases from 20% to 85%. But it increased gradually when the relative humidity varied from 85% to 98%.
On the other hand, the aerodynamic diameter of NaCl increased abruptly when the relative humidity varied from 75% to 98% in a larger way than bacterial aerosols. Lastly, PSL particles did not change at all.
The final increase ratio of aerodynamic diameter was 1.20 for B.subtilis , 1.34 for E.coli, 1.65 for NaCl and 0 for PSL. And it was equivalent to the hygroscopic growth factor (G=d/do).
