The ongoing Covid-19 pandemic has focused our attention on airborne droplet transmission. In this study, we simulate the dispersion of cough droplets in a tropical outdoor environment, accounting for the effects of non-volatile components on droplet evaporation. The effects of relative humidity, wind speed, and social distancing on evaporative droplet transport are investigated. Transmission risks are evaluated based on SARS-CoV-2 viral deposition on a person standing 1 m or 2 m away from the cougher. Our results show that the travel distance for a 100 µm droplet can be up to 6.6 m under a wind speed of 2 m/s. This can be further increased under dry conditions. We found that the travel distance of a small droplet is relatively insensitive to relative humidity. For a millimetric droplet, the projected distance can be more than 1 m, even in still air. Significantly greater droplets and viral deposition are found on a body 1 m away from a cougher, compared to 2 m. Despite low inhalation exposure based on a single cough, infection risks may still manifest through successive coughs or higher viral loadings.
REFERENCES
1.
Novel Coronavirus—China, World Health Organization
(WHO), retrieved 20 June 2020.
2.
S.
Asadi
, N.
Bouvier
, A. S.
Wexler
, and W. D.
Ristenpart
, “The coronavirus pandemic
and aerosols: Does COVID-19 transmit via expiratory particles?
,”
Aerosol Sci. Technol.
54
, 635
–638
(2020
).3.
L.
Bourouiba
, “Turbulent gas clouds and
respiratory pathogen emissions: Potential implications for reducing transmission of
COVID-19
,” JAMA
323
, 1837
–1838
(2020
).4.
R.
Tellier
, Y.
Li
, B.
J.
Cowling
, and J. W.
Tang
, “Recognition of aerosol
transmission of infectious agents: A commentary
,” BMC Infect.
Dis.
19
, 101
(2019
).5.
R.
Mittal
, R.
Ni
, and J.-H.
Seo
, “The flow physics of
COVID-19
,” J. Fluid Mech.
894
, F2-1
–F2-14
(2020
).6.
Y.
G.
Li
, H.
Qian
, J.
Hang
, X.
G.
Chen
, L.
Hong
, P.
Liang
, J. S.
Li
, S.
L.
Xiao
, J.
J.
Wei
, L.
Liu
, and M.
Kang
, “” (published online
2020
).7.
L.
Morawska
and J.
Cao
, “Airborne transmission of
SARS-CoV-2: The world should face the reality
,” Environ.
Int.
139
, 105730
(2020
).8.
J.
P.
Duguid
, “The size and the duration of
air-carriage of respiratory droplets and droplet-nuclei
,”
Epidemiol. Infect.
44
, 471
–479
(1946
).9.
W.
F.
Wells
, Airborne Contagion and Air Hygiene: An
Ecological Study of Droplet Infections
(Harvard University
Press
, 1955
).10.
X.
Xie
, Y.
Li
, H.
Sun
, and L.
Liu
, “Exhaled droplets due to talking
and coughing
,” J. R. Soc., Interface
6
, S703
–S714
(2009
).11.
L.
Bourouiba
, E.
Dehandschoewercker
, and J. W. M.
Bush
, “Violent expiratory events: On
coughing and sneezing
,” J. Fluid Mech.
745
, 537
–563
(2014
).12.
G.
A.
Somsen
, C.
van Rijn
, S.
Kooij
, R. A.
Bem
, and D.
Bonn
, “Small droplet aerosols in poorly
ventilated spaces and SARS-CoV-2 transmission
,” Lancet Respir.
Med.
8
, 658
–659
(2020
).13.
W.
F.
Wells
, “On air-borne infections: Study
II. Droplets and droplet nuclei
,” Am. J. Epidemiol.
20
, 611
–618
(1934
).14.
T.
F.
Booth
, B.
Kournikakis
, N.
Bastien
, J.
Ho
, D.
Kobasa
, L.
Stadnyk
, Y.
Li
, M.
Spence
, S.
Paton
, B.
Henry
, B.
Mederski
, D.
White
, D. E.
Low
, A.
McGeer
, A.
Simor
, M.
Vearncombe
, J.
Downey
, F. B.
Jamieson
, P.
Tang
, and F.
Plummer
, “Detection of airborne severe
acute respiratory syndrome (SARS) coronavirus and environmental contamination in SARS
outbreak units
,” J. Infect. Dis.
191
, 1472
–1477
(2005
).15.
X.
Xie
, Y.
Li
, A.
T. Y.
Chwang
, P. L.
Ho
, and W. H.
Seto
, “How far droplets can move in
indoor environments—Revisiting the wells evaporation–falling curve
,”
Indoor Air
17
, 211
–225
(2007
).16.
N.
van Doremalen
, T.
Bushmaker
, D. H.
Morris
, M. G.
Holbrook
, A.
Gamble
, B. N.
Williamson
, A.
Tamin
, J. L.
Harcourt
, N. J.
Thornburg
, S. I.
Gerber
, J. O.
Lloyd-Smith
, E.
de Wit
, and V. J.
Munster
, “Aerosol and surface stability
of SARS-CoV-2 as compared with SARS-CoV-1
,” N. Engl. J.
Med.
382
, 1564
–1567
(2020
).17.
P.
Y.
Chia
, K.
K.
Coleman
, Y. K.
Tan
, S.
W. X.
Ong
, M.
Gum
, S.
K.
Lau
, X.
F.
Lim
, A.
S.
Lim
, S.
Sutjip
, P. H.
Lee
, T.
T.
Son
, B.
E.
Young
, D. K.
Milton
, G. C.
Gray
, S.
Schuster
, T.
Barkham
, P. P.
De
, S.
Vasoo
, M.
Chan
, B.
S. P.
Ang
, B.
H.
Tan
, Y.
S.
Leo
, O.
T.
Ng
, and M. S. Y.
Wong
, “Detection of air and surface
contamination by SARS-CoV-2 in hospital rooms of infected patients
,”
Nat. Commun.
11
, 2800
(2020
).18.
X.
Li
, Y.
Shang
, Y.
Yan
, L.
Yang
, and J.
Tu
, “Modelling of evaporation of cough
droplets in inhomogeneous humidity fields using the multi-component Eulerian-Lagrangian
approach
,” Build. Environ.
128
, 68
–76
(2018
).19.
B.
Blocken
, F.
Malizia
, T.
van Druenen
, and T.
Marchal
, Toward aerodynamically equivalent COVID19 1.5
m social distancing for walking and running, http://www.urbanphysics.net/Social%20Distancing%20v20_White_Paper.pdf,
retrieved on 10 June 2020.20.
T.
Dbouk
and D.
Drikakis
, “On coughing and airborne
droplet transmission to humans
,” Phys. Fluids
32
, 053310-1
–053310-10
(2020
).21.
V.
Vuorinen
, https://www.aalto.fi/en/news/researchers-modelling-the-spread-of-the-coronavirus-emphasise-the-importance-of-avoiding-busy,
retrieved on 10 June 2020.22.
Y.
Feng
, T.
Marchal
, T.
Sperry
, and H.
Yi
, “Influence of wind and relative
humidity on the social distancing effectiveness to prevent COVID-19 airborne
transmission: A numerical study
,” J. Aerosol Sci.
147
, 105585
(2020
).23.
M.-R.
Pendar
and J. C.
Páscoa
, “Numerical modeling of the
distribution of virus carrying saliva droplets during sneeze and cough
,”
Phys. Fluids
32
, 083305-1
–083305-18
(2020
).24.
B.
Wang
, H.
Wu
, and X.-F.
Wan
, “Transport and fate of human
expiratory droplets—A modeling approach
,” Phys. Fluids
32
, 083307-1
–083307-13
(2020
).25.
S.
Chaudhuri
, S.
Basu
, P.
Kabi
, V.
R.
Unni
, and A.
Saha
, “Modeling the role of respiratory
droplets in COVID-19 type pandemics
,” Phys. Fluids
32
, 063309-1
–063309-12
(2020
).26.
See https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public
for World Health Organization, retrieved on 10 June 2020.
27.
Centres for Disease Control (Cdc) 2020, How
COVID-19 spreads, available at: https://www.cdc.gov/coronavirus/2019-ncov/prepare/transmission.html,
retrieved on 10 June 2020.
28.
See https://www.gov.sg/article/moving-into-phase-2-what-activities-can-resume
for activities that can resume, retrieved on 20 June 2020.
29.
J.
Redrow
, S.
Mao
, I.
Celik
, J. A.
Posada
, and Z.-G.
Feng
, “Modeling the evaporation and
dispersion of airborne sputum droplets expelled from a human cough
,”
Build. Environ.
46
, 2042
–2051
(2011
).30.
J.
K.
Gupta
, C.-H.
Lin
, and Q.
Chen
, “Flow dynamics and
characterization of a cough
,” Indoor Air
19
, 517
–525
(2009
).31.
A.
Bulińska
and Z.
Buliński
, “A CFD analysis of different
human breathing models and its influence on spatial distribution of indoor air
parameters
,” Comput. Assisted Methods Eng. Sci.
22
, 213
–227
(2015
), see
https://cames.ippt.pan.pl/index.php/cames/article/view/23.32.
P.
A.
Cundall
and O. D. L.
Strack
, “A discrete numerical model for
granular assemblies
,” Geotechnique
29
, 47
–65
(1979
).33.
S.
A.
Morsi
and A. J.
Alexander
, “An investigation of particle
trajectories in two-phase flow systems
,” J. Fluid Mech.
55
, 193
–208
(1972
).34.
J.
I.
Partanen
, “Re-evaluation of the mean
activity coefficients of strontium chloride in dilute aqueous solutions from (10 to 60)
°C and at 25 °C up to the saturated solution where the molality is 3.520
mol·kg−1
,” J. Chem. Eng. Data
58
, 2738
–2747
(2013
).35.
O.
C.
Bridgeman
and E. W.
Aldrich
, “Vapor pressure tables for
water
,” J. Heat Transfer
86
, 279
–286
(1964
).36.
W.
E.
Ranz
and W. R.
Marshall
, “Evaporation from drops. Part
I
,” Chem. Eng. Prog.
48
, 141
–146
(1952
), see
http://dns2.asia.edu.tw/∼ysho/YSHO-English/1000%20CE/PDF/Che%20Eng%20Pro48,%20141.pdf.37.
S.
S.
Sazhin
, “Advanced models of fuel droplet
heating and evaporation
,” Prog. Energy Combust. Sci.
32
, 162
–214
(2006
).38.
ANSYS FLUENT theory,
2019
.39.
M.
Nicas
, W. W.
Nazaroff
, and A.
Hubbard
, “Toward understanding the risk
of secondary airborne infection: Emission of respirable pathogens
,”
J. Occup. Environ. Hyg.
2
, 143
–154
(2005
).40.
A.
A.
Borisov
, B. E.
Gel’fand
, M. S.
Natanzon
, and O. M.
Kossov
, “Droplet breakup regimes and
criteria for their existence
,” J. Eng. Phys.
40
, 44
–49
(1981
).41.
L.
Morawska
, “Droplet fate in indoor
environments, or can we prevent the spread of infection?
,”
Indoor Air
16
, 335
–347
(2006
).42.
See http://www.weather.gov.sg/climate-climate-of-singapore/ for Meteorological
Service Singapore, retrieved on 10 May 2020.
43.
K.
K.-W.
To
, O.
T.-Y.
Tsang
, C. C.-Y.
Yip
, K.-H.
Chan
, T.-C.
Wu
, J.
M.-C.
Chan
, W.-S.
Leung
, T. S.-H.
Chik
, C.
Y.-C.
Choi
, D.
H.
Kandamby
, D. C.
Lung
, A.
R.
Tam
, R.
W.-S.
Poon
, A.
Y.-F.
Fung
, I.
F.-N.
Hung
, V.
C.-C.
Cheng
, J. F.-W.
Chan
, and K.-Y.
Yuen
, “Consistent detection of 2019
novel coronavirus in saliva
,” Clin. Infect. Dis.
71
, 841
–843
(2020
).44.
S.
H.
Smith
, G. A.
Somsen
, C.
van Rijn
, S.
Kooij
, L.
vander Hoek
, R. A.
Bem
, and D.
Bonn
, “,” (published online
2020
).45.
M.
M.
Arons
, K. M.
Hatfield
, S. C.
Reddy
, A.
Kimball
, A.
James
, J. R.
Jacobs
, J.
Taylor
, K.
Spicer
, A. C.
Bardossy
, L. P.
Oakley
, S.
Tanwar
, J. W.
Dyal
, J.
Harney
, Z.
Chisty
, J. M.
Bell
, M.
Methner
, P.
Paul
, C.
M.
Carlson
, H. P.
McLaughlin
, N.
Thornburg
, S.
Tong
, A.
Tamin
, Y.
Tao
, A.
Uehara
, J.
Harcourt
, S.
Clark
, C.
Brostrom-Smith
, L. C.
Page
, M.
Kay
, J.
Lewis
, P.
Montgomery
, N. D.
Stone
, T. A.
Clark
, M. A.
Honein
, J. S.
Duchin
, and J. A.
Jernigan
, “Presymptomatic SARS-CoV-2
infections and transmission in a skilled nursing facility
,” N.
Engl. J. Med.
382
, 2081
–2090
(2020
).46.
F.
Yu
, L.
Yan
, N.
Wang
, S.
Yang
, L.
Wang
, Y.
Tang
, G.
Gao
, S.
Wang
, C.
Ma
, R.
Xie
, F.
Wang
, C.
Tan
, L.
Zhu
, Y.
Guo
, and F.
Zhang
, “Quantitative detection and viral
load analysis of SARS-CoV-2 in infected patients
,” Clin. Infect.
Dis.
71
, 793
–798
(2020
).47.
N.
R.
Jones
, Z. U.
Qureshi
, R. J.
Temple
, J. P. J.
Larwood
, T.
Greenhalgh
, and L.
Bourouiba
, “Two metres or one: What is
the evidence for physical distancing in COVID-19?
,” BMJ
370
, m3223
(2020
).48.
Y.
Wang
, H.
Tian
, L.
Zhang
, M.
Zhang
, D.
Guo
, W.
Wu
, X.
Zhang
, G. L.
Kan
, L.
Jia
, D.
Huo
, B.
Liu
, X.
Wang
, Y.
Sun
, Q.
Wang
, P.
Yang
, and C. R.
MacIntyre
, “Reduction of secondary
transmission of SARS-CoV-2 in households by face mask use, disinfection and social
distancing: A cohort study in Beijing, China
,” BMJ Global
Health
5
, e002794
(2020
).© 2020 Author(s).
2020
Author(s)
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