Effects of applied energy on the generation of novel condensation aerosols

Efficient production of condensation aerosols from the capillary aerosol generator (CAG) requires sufficient thermal energy to vaporize the formulation. Aerosolization efficiency and particle size characteristics of model solute aerosols have been investigated as a function of applied energy.; Using a propylene glycol (PG) formulation, CAG aerosols were generated at increasing applied energies. Efficient aerosolization of PG (35 mg) was achieved at about 40--45 J, with a mean (SD) MMAD of 0.9 (0.04) mum. Further increasing the applied energy produced an increase in PG MMADs from about 0.9 to 1.7 mum. This may have been due to a decreased PG vapor nucleation rate at higher applied energies.; The effects of applied energy on CAG aerosol characteristics following the addition of individual solutes to the PG formulation were also investigated. Solutes of decreasing volatility, benzil (BZ) > caffeine (CA) > deoxycorticosterone (DOC), at solution concentrations of 12 mM in PG solution (35mg), respectively, did not appear to affect total aerosol aerosolization efficiency. Efficient solute aerosolization was achieved above their respective energy thresholds of about 38, 38 and 40 J. The mean (SD) solute MMADs measured in the "energy sufficient" region were 0.97 (0.06), 0.86 (0.04) and 0.65 (0.11) mum, respectively, for BZ, CA and DOC. The addition of BZ and CA appeared to have only a small effect at the higher applied energies on the aerosol formation mechanism. In contrast, DOC aerosols exhibited a significant solute effect, probably due to its lower relative volatility.; 3, 12 and 94 mM DOC/PG formulations were employed to study the effects of solute concentration on aerosol formation at different applied energies. At the lowest DOC concentration, the effect of the solute on the aerosol formation mechanism was minimal and the aerosol size characteristics as a function of applied energy were similar to those observed with BZ and CA. Increasing the DOC concentration, produced aerosols whose particle size distributions, above the energy threshold, were independent of applied energy. The solute particle size decreased with increasing DOC concentration and exhibited two modes, an ultrafine fraction and a fraction distributed within PG droplets.