Characterization of Aerosols Generated by Exhalation and Inhalation of Bottlenose Dolphins*

To begin to understand the exposure and risk posed to marine mammals during and after an oil spill, we characterized the evolution of airborne droplets and flow field during exhalation and inhalation of trained bottlenose dolphins at National Aquarium in Baltimore. High speed holograms covering the entire plumes were recorded during multiple normal (NB), chuff (CB) and post-exercise (PEB) breaths by dolphins differing in age, size, sex, and athleticism. The air velocity was inferred from micro-droplet speeds accounting for gravity effects. Most of the airborne droplets were smaller than 120 µm, but some ejecta with odd shapes extended to several mm. Each exhalation had multiple velocity peaks. PEB had higher peak air velocities (5.5-7 m/s) than CB (4-5.5 m/s) or NB (3.5-6 m/s), irrespective of size or sex. The duration of exhalation was longer for NB (200-400 ms) compared to that of CB or PEB (150-250 ms). Most of the calculated air volumes per breath ranged between 2 to 4 L, peaking at 7 L, and the exhaled liquid volumes varied from 1 to 30 mL. Inhalation occurred at steady speeds (0.5-1 m/s) for 600 ms or longer, and the inhaled liquid volumes mostly varied from 0.05 to 0.4 mL, with peaks of 1 mL. These measurements are guiding design and calibration of a mechanism that mimics dolphin breaths for use in laboratory tests involving crude oil.