Exhaled particles from nanometre to millimetre and their origin in the human respiratory tract

Detailed knowledge of the properties of exhaled particles from the human respiratory tract for all genders and ages is essential to determine the modes of transmission of airborne diseases. This applies not only to the current COVID-19 pandemic, but also to many others, be it measles, seasonal influenza or tuberculosis. To date, there are no data on the individual-specific concentrations and sizes of exhaled particles over the entire size range from nanometre to millimetre. Here we present a comprehensive data set, measured by particle size spectrometry and in-line holography covering the entire size range from 132 healthy volunteers aged 5 to 80 years for a defined set of breathing and vocalisation activities. We find age to have a large effect on small particle concentrations (<5 microns), doubling in children during adolescence and in adults over a 30-year period. In contrast, gender, body mass index, smoking or exercise habits have no discernible influence. Particles >20 microns show on average no measurable dependence on the type of vocalisation with the exception of shouting. We show evidence that particles <5 microns mainly originate in the lower respiratory tract, 5-15 microns in the larynx/pharynx, and >15 microns in the oral cavity.