TECHNIQUE FOR ASSESSING THE ELECTRICAL CHARGE LEVELS OF AEROSOLS

A relatively low-cost and easy-to-use method for estimating the charge level on aerosols has been developed. II uses the properties of an el ectrostatically enhanced (electret) filter combined with an optical pa l-tide counter to obtain size-dependent char-ge levels of workplace ae rosols. The optical particle counter is calibrated to give a ''filtrat ion equivalent'' particle size. For the size range of the present meas urements, this is similar to geometric size. The aerosol concentration is measured before and after neutralization to deter-mine a penetrati on ratio that can be approximately correlated with particle electrical mobility. For a particle of a given size, the penetration ratio incre ases with increasing particle charge level. The method was calibrated with monodisperse methylene blue particles charged to a known level. A polydisperse CaCO3 aerosol, characterized as to size-dependent charge levels, also was measured. Finally, the charge level on a copy-machin e toner dust was measured to simulate a highly charged workplace aeros ol. The method is limited to the size range of 0.1 mu m to 0.7 mu m by the characteristics of the electret filter. Electrical mobilities ran ging from 0.01 to 1 cm(2)/statV sec can be measured. The charge level on one particle size in a size distribution is proportional to the cha rge on other sizes, and can thus be al? indicator of charge level of t he overall aerosol. Although of limited size-range capability, the met hod can serve as an indicator of the importance of aerosol charge for sampling or for health effects.