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Measurement of electrical charges on airborne microorganisms
J Aerosol Sci. Vol. 31, Suppl. I, pp. $957 $958, 2000
Pergamon
www.elsevier.com/locate/jaerosci
Session 9A - Bioaerosols MEASUREMENT OF ELECTRICAL CHARGES ON AIRBORNE MICROORGANISMS
K. WILLEKE I, G. MAINELIS I, S.A. GR1NSHPUN 1, T. REPONEN 1, and P. BARON 2 Aerosol Research and Exposure Assessment Laboratory, Department of Environmental Health, University of Cincinnati, P.O. Box 670056, Cincinnati, OH 45267-0056; USA 2 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226-1998, USA.
Keywords: bioserosols, aerosol charging, sampling INTRODUCTION Our earlier research has shown that the collection of airborne microorganisms by electrostatic forces can be gentle and efficient. However, if the microorganisms are electrically charged in the sampler's inlet, sensitive bacteria may become non-viable from stress induced by the charging process (Mainelis et al., 1999). We have now investigated dispersion conditions which result in sufficient charges on the microorganisms so that electrically charging them for subsequent electrostatic removal from the sampled aerosol flow is not necessary. METHODS In order to investigate the electrical charges on airborne bacteria, we designed and built a system in which the test bacteria are aerosolized from a liquid suspension and the liquid in the bacteria-containing droplets is then evaporated by the addition of a drying air stream. The bacteria then enter a specially designed parallel plate mobility analyzer in which an adjustable electric field channels the bacteria of a specific electrical charge range into the mobility analyzer's outlet. By measuring the concentrations of bacteria in pre-selected electrical charge ranges and comparing them with the total concentration of airborne bacteria, we have obtained the electrical charge distribution on the airborne bacteria. We used an optical single particle counter'for these measurements (Model 1.108, Grimm Technologies Inc., Douglasville, Georgia, USA). The entire test system was placed in a Class 11, Type B2, biological safety cabinet (SterilchemGARD; Baker Company, Sanford, Maine, USA) so that all uncollected bacteria were properly disposed off. The temperature was kept at 22-260 C and the relative humidity at 30-50% during all experiments. RESULTS Our dispersion tests with Pseudomonasfluorescens bacteria, commonly found in air environments, have shown that the aerosolized bacteria have a net negative charge, and that individual bacteria can be highly charged, either negatively or positively. When the bacterial suspension was aerosolized with a Collison Nebulizer (BGI Inc., Waltham, Massachusetts, USA) while the nebulizer housing was removed, the bacteria acquired an electrical charge distribution ranging from about 13,000 negative to about 13,000 positive charges. Fifty percent of these bacteria carried between -1,000 and +400 elementary charges (Mainelis et al., 2000). In contrast, NaCI particles of the same size range (0.65-0.8 ~tm) acquired only between 1000 negative and 1000 positive charges. Fifty percent of these particles carried between -70 and +70 elementary charges.
S957
$958
Abstracts of the 2000 European Aerosol Conti:rcnce
We found that the amount of electrical charge carried by airborne bacteria depends on the dispersion method. When the same P. fluorescens bacteria were aerosolized from a Bubbling Aerosol Generator (Ulevicius et al. 1997), the bacteria acquired maximum electrical charges of only +1,500; fifty percent of the bacteria had between -200 and +150 electrical charges. We hypothesize that the difference in acquired electrical charge between the two dispersion methods is caused by the difference in liquiddisrupting force during droplet formation, and the type and proximity of a solid surface during droplet formation. Once a droplet containing a bacterium inside has acquired a charge, that electric charge remains on the bacterium after the liquid content of the droplet has evaporated. Thus, the charge carried by a bacterium consists of two components: its own natural charge, which can be high, and the charge imposed on it by the dispersion process. The liquid disrupting forces inside the Bubbling Aerosol Generator are weaker than those created by the compressed air inside the Collison Nebulizer, and, thus, the bacteria aerosolized by the Bubbling Aerosol Generator carry fewer charges than those aerosolized by the Collison Nebulizer. In the latter nebulizer, in addition to the liquid-disrupting forces, the liquid flow through the orifice may impart additional significant charges on the droplets by tribo-electrification. CONCLUSIONS Human and animals may emit small droplets with bacteria into the environment during exhalation. Waterborne bacteria may be dispersed by wind and wave actions. Future field studies will show to what extent airborne microorganisms in indoor and outdoor environments can be collected by electrical field forces without first electrically charging them. ACKNOWLEDGEMENTS This work was supported by the U.S. National Institute for Occupational Safety and Health through Grant No. RO 1-OH03463. REFERENCES Mainelis, G., Grinshpun, S.A., Willeke, K., Reponen, T., Ulevicius, V. and Hintz, P. (1999) Collection of Airborne Microorganisms by Electrostatic Precipitation, Aerosol Science and Technology, 30(2): 127-144. Mainelis, G., Willeke, K., Baron, P., Grinshpun, S.A., and Reponen, T. (In preparation) Electrical Charges on Aerosolized Microorganisms. Ulevicius, V., Willeke, K., Grinshpun, S.A., Donnelly, J., Lin, X. and Mainelis, G. (1997) Aerosol Generation by Bubbling Liquid: Characteristics and Generator Development, Aerosol Science and Technology, 26(2): 175-190.
Pergamon
www.elsevier.com/locate/jaerosci
Session 9A - Bioaerosols MEASUREMENT OF ELECTRICAL CHARGES ON AIRBORNE MICROORGANISMS
K. WILLEKE I, G. MAINELIS I, S.A. GR1NSHPUN 1, T. REPONEN 1, and P. BARON 2 Aerosol Research and Exposure Assessment Laboratory, Department of Environmental Health, University of Cincinnati, P.O. Box 670056, Cincinnati, OH 45267-0056; USA 2 Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226-1998, USA.
Keywords: bioserosols, aerosol charging, sampling INTRODUCTION Our earlier research has shown that the collection of airborne microorganisms by electrostatic forces can be gentle and efficient. However, if the microorganisms are electrically charged in the sampler's inlet, sensitive bacteria may become non-viable from stress induced by the charging process (Mainelis et al., 1999). We have now investigated dispersion conditions which result in sufficient charges on the microorganisms so that electrically charging them for subsequent electrostatic removal from the sampled aerosol flow is not necessary. METHODS In order to investigate the electrical charges on airborne bacteria, we designed and built a system in which the test bacteria are aerosolized from a liquid suspension and the liquid in the bacteria-containing droplets is then evaporated by the addition of a drying air stream. The bacteria then enter a specially designed parallel plate mobility analyzer in which an adjustable electric field channels the bacteria of a specific electrical charge range into the mobility analyzer's outlet. By measuring the concentrations of bacteria in pre-selected electrical charge ranges and comparing them with the total concentration of airborne bacteria, we have obtained the electrical charge distribution on the airborne bacteria. We used an optical single particle counter'for these measurements (Model 1.108, Grimm Technologies Inc., Douglasville, Georgia, USA). The entire test system was placed in a Class 11, Type B2, biological safety cabinet (SterilchemGARD; Baker Company, Sanford, Maine, USA) so that all uncollected bacteria were properly disposed off. The temperature was kept at 22-260 C and the relative humidity at 30-50% during all experiments. RESULTS Our dispersion tests with Pseudomonasfluorescens bacteria, commonly found in air environments, have shown that the aerosolized bacteria have a net negative charge, and that individual bacteria can be highly charged, either negatively or positively. When the bacterial suspension was aerosolized with a Collison Nebulizer (BGI Inc., Waltham, Massachusetts, USA) while the nebulizer housing was removed, the bacteria acquired an electrical charge distribution ranging from about 13,000 negative to about 13,000 positive charges. Fifty percent of these bacteria carried between -1,000 and +400 elementary charges (Mainelis et al., 2000). In contrast, NaCI particles of the same size range (0.65-0.8 ~tm) acquired only between 1000 negative and 1000 positive charges. Fifty percent of these particles carried between -70 and +70 elementary charges.
S957
$958
Abstracts of the 2000 European Aerosol Conti:rcnce
We found that the amount of electrical charge carried by airborne bacteria depends on the dispersion method. When the same P. fluorescens bacteria were aerosolized from a Bubbling Aerosol Generator (Ulevicius et al. 1997), the bacteria acquired maximum electrical charges of only +1,500; fifty percent of the bacteria had between -200 and +150 electrical charges. We hypothesize that the difference in acquired electrical charge between the two dispersion methods is caused by the difference in liquiddisrupting force during droplet formation, and the type and proximity of a solid surface during droplet formation. Once a droplet containing a bacterium inside has acquired a charge, that electric charge remains on the bacterium after the liquid content of the droplet has evaporated. Thus, the charge carried by a bacterium consists of two components: its own natural charge, which can be high, and the charge imposed on it by the dispersion process. The liquid disrupting forces inside the Bubbling Aerosol Generator are weaker than those created by the compressed air inside the Collison Nebulizer, and, thus, the bacteria aerosolized by the Bubbling Aerosol Generator carry fewer charges than those aerosolized by the Collison Nebulizer. In the latter nebulizer, in addition to the liquid-disrupting forces, the liquid flow through the orifice may impart additional significant charges on the droplets by tribo-electrification. CONCLUSIONS Human and animals may emit small droplets with bacteria into the environment during exhalation. Waterborne bacteria may be dispersed by wind and wave actions. Future field studies will show to what extent airborne microorganisms in indoor and outdoor environments can be collected by electrical field forces without first electrically charging them. ACKNOWLEDGEMENTS This work was supported by the U.S. National Institute for Occupational Safety and Health through Grant No. RO 1-OH03463. REFERENCES Mainelis, G., Grinshpun, S.A., Willeke, K., Reponen, T., Ulevicius, V. and Hintz, P. (1999) Collection of Airborne Microorganisms by Electrostatic Precipitation, Aerosol Science and Technology, 30(2): 127-144. Mainelis, G., Willeke, K., Baron, P., Grinshpun, S.A., and Reponen, T. (In preparation) Electrical Charges on Aerosolized Microorganisms. Ulevicius, V., Willeke, K., Grinshpun, S.A., Donnelly, J., Lin, X. and Mainelis, G. (1997) Aerosol Generation by Bubbling Liquid: Characteristics and Generator Development, Aerosol Science and Technology, 26(2): 175-190.