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Representative samples of three participants (P5, P7, and P8). Particle number concentration exhaled over time on a logarithmic scale with the various oxygen modalities and respiratory maneuvers are shown. White colored rectangles denote background room measurements. C = coughing; D = deep breathing; FM = face mask; HFNC = heated and humidified high-flow nasal cannula; N = normal breathing; NC = nasal cannula; NIPPV = noninvasive positive-pressure ventilation; T = talking.
