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The charge distribution of aerosol is an important factor for accurate prediction of aerosol behavior as it influences particle transport, settling, deposition, and coagulation. In the production of aerosol for pulmonary drug delivery, charging of aerosol particles is influenced by both the generation method and chemical properties of the drug. Electrostatic charging of add-on devices such as plastic spacers and holding chambers will reduce the delivery to the lung, while charged particles can also enhance deposition to the respiratory system by inducing an image charge to airway surfaces. Typical target particle size for delivery devices in terms of mass median aerodynamic diameter (MMAD) is 1-5 μm, and therefore up to 50% of the dose includes submicron particles in the fine (100-1000 nm) and ultrafine ( < 100 nm) size range. Measurement of the charge distribution of submicron particles produced using a vibrating mesh nebulizer is presented using a tandem differential mobility analyzer (TDMA). It is found that the charge distribution is not at equilibrium, but instead has an increase in the fraction of charged particles below 200 nm and a decrease in the charged fraction above 200 nm. In general the charge distribution will be dependent on the specific aerosol nebulizer setup being used and the chemical properties of the nebulized solution, and it could be further quantified by using the methods discussed here.

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