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Differential synthetic schlieren images of the thermal plumes produced by a person in a quiescent environment. In panels (a–c) no mask is worn, while in panels (d–f) a non-surgical three-ply disposable mask is worn. The subject is (a,d) sitting quietly breathing through their nose, (b,e) saying ‘also’ when speaking at a conversational volume and (c,f) laughing. Video sequences of each of these can be found in the supplementary material.
