Characterization of Nanoaerosol Size Change During Enhanced Condensational Growth.

Increasing the size of nanoaerosols may be beneficial in a number of applications including filtration, particle size selection, and targeted respiratory drug delivery. A potential method to increase particle or droplet size is enhanced condensational growth (ECG), which involves combining the aerosol with saturated or supersaturated air. In this study, we characterize the ECG process in a model tubular geometry as a function of initial aerosol size (mean diameters - 150, 560 and 900 nm) and relative humidity conditions using both in vitro experiments and numerical modeling. Relative humidities (99.8 - 104%) and temperatures (25 - 39 °C) were evaluated that can safely be applied to either targeted respiratory drug delivery or personal aerosol filtration systems. For inlet saturated air temperatures above ambient conditions (30 and 39 °C), the initial nanoaerosols grew to a size range of 1000 - 3000 nm (1 - 3 μm) over a time period of 0.2 seconds. The numerical model results were generally consistent with the experimental findings and predicted final to initial diameter ratios of up to 8 after 0.2 s of humidity exposure and 14 at 1 s. Based on these observations, a respiratory drug delivery approach is suggested in which nanoaerosols in the size range of 500 nm are delivered in conjunction with a saturated or supersaturated air stream. The initial nanoaerosol size will ensure minimal deposition and loss in the mouth-throat region while condensational growth in the respiratory tract can be used to ensure maximal lung retention and to potentially target the site of deposition.