Measurement of electrical charges carried by airborne bacteria laboratory-generated using a single-pass bubbling aerosolizer

Widely used bioaerosol generators like Collison nebulizer probably produce electrostatically charged particles, but the electrical charges carried by laboratory-generated airborne microorganisms using bubbling aerosolizers are poorly understood. In this study, we measured the fraction of neutral particles and number of elementary charges per particle as a function of the aerodynamic diameter of airborne bacteria (Escherichia coli and Enterococcus hirae). Bioaerosols were produced by a liquid sparging aerosolizer-type bubbling generator, with particle sizes ranging from roughly 0.6 to 2 μm. The experimental setup included an electrostatic precipitator and real-time devices including an electrometer, aerodynamic particle sizer, and electrical low-pressure impactor. Experimental results obtained for various operating conditions showed that aerosols produced with a higher bubbling airflow contained a larger proportion of neutral particles (from around 30% to 50%) and that bacteria carried a greater average absolute number of elementary charges (from around –10 to –60 elementary units) than those under lower airflow. Under the investigated conditions, a neutralization step is unnecessary because it may have a negative effect on the viability of sensitive microorganisms. Our results suggest that the neutral fraction can be used downstream of an electrostatic precipitator, and that this setup may have advantages over bipolar neutralizers.