Comparative time-resolved measurements of aerosol plume size distributions at two relative humidities using a comparative hygroscopic aerodynamic particle sizing approach

The aerodynamic size distribution of therapeutic particles actuated from an inhaler is an important parameter when optimising the delivery of drugs by the respiratory route. The size distribution influences the deposition pattern of the aerosol in the lungs and, thus, impacts on the delivered dose and efficacy of the treatment. We demonstrate here the utility of the Comparative hygroscopic Aerosol Particle Sizing (CHAPS) method for analysing temporal variations in nebulized sodium chloride aerosol particle size distributions with a time-resolution of one second, simultaneously reporting distributions at two different relative humidities (RHs). We compare particle size distributions measured at relative humidities of 40% - 60%, representative of the ambient environment, and above 90%, approaching that in the lung environment. The CHAPS method not only provides insights into the real-time dynamics of aerosol plume development, but also allows direct measurement of the variability in delivered aerosol dose, actuation by actuation. We also compare the degree of hygroscopic growth in aerosol size reported by the CHAPS concurrently at two RHs, confirming that sizes are consistent with equilibrated aerosol. This method could be used to study aerosols generated by Soft Mist Inhalers (SMI), pressurized metered-dose inhalers (pMDI), and dry powder inhalers (DPI).