singers perform a broad range of genres, including musical theatre (6), choral (5), opera (5), and other genres: gospel (2), rock (2), jazz (2), pop (1), actor with singing interest (1) and soul (1). 6 identified their voice-type as soprano or mezzo-soprano, 7 as alto, 5 as tenor and 7 as bass or baritone. Aerosols and droplet concentrations were measured with an Aerodynamic Particle Sizer (APS, 500 nm -20 µm) in an operating theatre with each participant and researcher required to wear appropriate personal protective equipment. The high air exchange rate, filtration and laminar air flow reduced the pre-existing particle background number concentration to zero cm -3 , enabling the unique and extremely sensitive measurements described. Thus, any particles detected were directly attributable to participant activity, with particle concentrations returning to zero cm -3 between periods of singing, speaking and breathing.