Table 1.

Particle size of exhaled aerosol under variable breathing conditions by healthy and infected patients.

Breathing maneuver	Particle size	Other essential data and remarks	Ref.
Mouth breathing, nose breathing, coughing, talking	The majority of particles are below 0.6 μm	Concentration of droplets ≤1 μm: -up to ∼180 dm−3 for coughing -up to ∼30 dm−3 for mouth breathing and talking -up to 11 dm−3 for nose breathing Concentration of droplets >1 μm: -up to 35 dm−3 for coughing -up to 6 dm−3 for mouth breathing -up to ∼4.5 dm−3 for talking -up to ∼1.5 dm−3 for nose breathing	[34]
Breathing with different intensity and breath-holding	Modal value of droplet diameter ∼ 1 μm	Reduction of the number of exhaled droplets by breath-holding suggests that they are formed in bronchioles during inhalation (they sediment in the alveoli during breath-holding)	[44]
Breathing, vocalization, speech, cough	The majority of droplets are < 0.8 μm for all activities	Total droplet concentration: -breathing: 100 dm−3 -sustained vocalization and cough: 1100 dm−3 Unimodal size distribution (∼0.8 μm) for breathing, bimodal for vocalization (modes (∼0.8 and 1.8 μm), trimodal for speech (∼0.8, 1.8 and 3.5–5 μm)	[38]
Speaking, coughing	Median diameter (count): 13.5 μm cough 16.5 μm speech	Droplet size distribution measured with interferometric Mie imaging Droplet concentration: -Speech: 4–220 dm−3 -Cough: 2400–5200 dm−3 (i.e. up to 2000 droplet per cough) Droplet velocity: -3.9 m/s for speaking -11.7 m/s for coughing	[45]
Speaking, coughing	Droplet size range: 10–100 μm	Measuring method: solid impaction and microscopy. The majority of droplets were 35–50 μm for speaking and 35–100 μm for coughing	[40]
Sneezing	Droplet size range 20–1000 μm (volume-based droplet size distribution	Unimodal or bimodal size distribution with volumetric mode diameter equal: 360 μm (unimodal) 72 and 386 μm (bi-modal)	[41]
Breathing, speech, sustained vocalization, coughing	Droplets in the size range of 0.1–1000 μm	Generation of droplets in the lower respiratory tract (bronchial fluid film burst), larynx (voicing/coughing), and oral cavity (speech and coughing) results in trimodal droplet size distribution. Mode diameters: -for speech: 1.6, 2.5, 145 μm -for cough: 1.6; 1.7 and 123 μm	[46]
Cough of patients with influenza: active and recovered	Droplet size range 0.35–10 μm, the majority < 3 μm (63% in the respirable size fraction) count median diameter: 0.63 μm	Number of droplets: 900–300 000 droplets per cough (active or recovered patients)	[47]
Oral and nasal breathing of various dynamics, speech with various loudness	97% droplets < 1 μm		[48]
Speech	Droplet size range: 0.05–10 μm; geometric mean diameter (number-based) ∼1 μm, regardless of voice amplitude	The number of emitted droplets increases with speech loudness from <100 dm−3 up to 300 dm−3 Vocalization activates laryngeal particle generation	[39]
Cough and cough with covering (hand, tissue, surgical mask)	The majority of droplets <0.5 μm	Droplet concentration: up to 300 dm−3 No essential filtration effect of submicrometer particles by covering of mouth with hand, sleeve, tissue or surgical mask	[49]
Breathing by patients infected with human rhinovirus (HRV)	80% of exhaled droplets in 0.3–0.5 μm diameter range	Droplet concentration: up to 7200 dm−3 for exhalation with tidal volume. No HRV detected in collected breath samples	[50]