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2635988 
Journal Article 
Modality of human expired aerosol size distributions 
Johnson, GR; Morawska, L; Ristovski, ZD; Hargreaves, M; Mengersen, K; Chao, CYH; Wan, MP; Li, Y; Xie, X; Katoshevski, D; Corbett, S 
2011 
Yes 
Journal of Aerosol Science
ISSN: 0021-8502
EISSN: 1879-1964 
42 
12 
839-851 
WOS:000296165100001 
An essential starting point when investigating the potential role of human expired aerosols in the transmission of disease is to gain a comprehensive knowledge of the expired aerosol generation process, including the aerosol size distribution, the various droplet production mechanisms involved and the corresponding sites of production within the respiratory tract. In order to approach this level of understanding we have integrated the results of two different investigative techniques spanning 3 decades of particle size from 700 nm to 1 mm, presenting a single composite size distribution, and identifying the most prominent modes in that distribution. We link these modes to specific sites of origin and mechanisms of production. The data for this were obtained using the Aerodynamic Particle Sizer (APS) covering the range 0.7 <= d <= 20 mu m and Droplet Deposition Analysis (DDA) covering the range d >= 20 mu m.



In the case of speech three distinct droplet size distribution modes were identified with count median diameters at 1.6, 2.5 and 145 mu m. In the case of voluntary coughing the modes were located at 1.6, 1.7 and 123 mu m. The modes are associated with three distinct processes: one occurring deep in the lower respiratory tract, another in the region of the larynx and a third in the upper respiratory tract including the oral cavity. The first of these, the Bronchiolar Fluid Film Burst (BFFB or B) mode contains droplets produced during normal breathing. The second, the Laryngeal (L) mode is most active during voicing and coughing. The third, the Oral (O) cavity mode is active during speech and coughing. The number of droplets and the volume of aerosol material associated with each mode of aerosol production during speech and coughing is presented. The size distribution is modeled as a tri-modal lognormal distribution dubbed the Bronchiolar/Laryngeal/Oral (B.L.O.) tri-modal model. (C) 2011 Elsevier Ltd. All rights reserved. 
Human expired aerosol; BLO tri-modal model; Size distribution; Modality; Bronchiolar; Laryngeal