                  
2150mmTalking

Coughing

In medical studies, particles released fromoral cavity are distinguished between
aerosols and droplets at a diameter of 5 m.
The actual size distribution of particles
released from the oral cavity is two-peaked,
with 150 m droplets falling in about twoseconds and reaching only about two meters,
while 2 m aerosols drift in the air for a longtime. In some cases, the droplets isdehydrated to form aerosol-sized droplet
nuclei.

1) Suction
Silent type fan
Contaminated
air contains
droplets

Fall down speed (m/s)

The filter with visiblelight-responsible
photocatalyst

Purified air

Aerosol !

SARS-CoV-2
Virus

Droplets captured on the filter

2) Capture

Droplets changes to droplet
nuclei with dehydration in air

G.R. Jhonson et al., Modality of human expired aerosol size distributions,
J. Aerosol Science, 42(2011)839-851.

Droplets that would
usually reach thefacing person

Droplets released
from the oral cavityDiameter( m)3) Decompose

Visible LED modules" Droplet

Within 2m5 m(Typical width of meeting table
is about 80cm)

Nobuyuki Takegawa, Aerosol, Droplet Transmission, andAirborne Transmission, Earozoru Kenkyu, 36 (2021) 65-74.

                

Light (Photon)

NOT commercial productParticle of
Photocatalyst

Reaction in photocatalyst

Visible light#380nm$, 3.1eV$%

Reduction

O2Conduction band
Band Gap

Shading leaked light with Japanese paper      The size is 12 cm square and5 cm high. Fan noise is only
19 dB. Power consumption isless than 5 W, and can be
powered by a mobile battery

Using visible light-responsive photocatalyst, it does notneed to be completely shielded from leaking light and canbe made with a simple structure. It is made by combining
commercial PC parts, therefore it cost only 1200 yen perunit. The photocatalyst filter can be manufactured with asimple non-woven fabric filter and Toshiba's "Renecat"
spray, which is commercially available. The suction
performance can be improved by using a more powerful fan.

       

Excitedby light&O2-Oxidizing power
higher than ozone

e- Electron

H2Oh+Valence band

holeTiO2(anatase) 3.2eV &OHOxidationneed UV-light

Because reactive oxygen
species disappear in about
one millionth of a second,
they can only move to a few
microns from the surface.

WO3 2.5eV            Excited byvisible light($495nm)

Finally organic materials are breaking down
completely into water and CO2

!      A duct was set up in a cleanbooth using HEPA filter unit, andthe rate at which ultrasonicsprayer mist, simulating dropletsfrom the oral cavity, was captured
by a non-woven fabric filter wasevaluated. As a result, it wasconfirmed that droplets of 5 m
or larger could be almost
completely captured.

Special video recording wasconducted to visualize droplets inthe air. Within a range of about
50cm, we can see that droplets
emitted by speech from the oralcavity with a "booming" sound areinhaled and stopped by the filterin the same way as a mask.

     

The non-woven fabric filter used in this study"     
Air flow
0.3 m/s

300mm

500mm
PCXNebulizer:
nozzle height
400mm

Small Droplet
remover: puton the deskParticle counter:nozzle height
400mm

Large clean booth: 1.5'1.5'2.4m

Density of Particles / m

-3

109
108

107

Performance of the small droplet remover inopen space was estimated using large cleanbooth. Particle counters were placed offcenter axis of nebulizer and the remover. The
nozzle of the nebulizer was set horizontallyand the mist flied almost straight with afollowing wind of 0.3 m/s from air purifier units.

106
105

Particle Counter Height 400 mm
Particle size 1-5 m, Cleaner OFF
Particle size 1-5 m, Cleaner ON
Particle size 5-25 m, Cleaner OFF
Particle size 5-25 m, Cleaner ON104
103

0100200

PCX: position of Particle Counter / mm

Large droplets with diameters of 5.0 to 25m were reduced to about 1/10 in all
position. Aerosols of 1.0 to 5.0 m, which
are close to the peak diameter of the aerosol
emitted from the actual oral cavity, were also
reduced to about 1/10 from center to 15cm,but at 20 and 25cm almost no reduction wasobserved.

     5
k=8.84#10-4/min

Infectivity / PFU  

HCHO density / mg!m-3

 

k1=1.81#10-2/min
k2=1.41#10-3/min

k1=2.35#10-2/min
k2=7.15#10-5/min

1

0.50

k=1.76#10-2/min

k=3.81#10-2/min

100

106
Blank
With small droplets remover

k=6.70#10-3/min

Blank
Standard nonwoven fabric filter
Nonwoven fabric filter + 10wt% WO 3 slurry
Ceramic fiber paper + 10wt% WO 3 slurry
Ceramic fiber paper after 500" baking + 10wt% WO 3 slurry
Glass fiber mesh + 10wt% WO 3 slurry

200
Time / min300

105010Time / min

20400

Using a 38L size acrylic desiccator,changes in the concentration offormaldehyde (HCHO), a kind of organic
gas, were measured using a formaldehyde
meter htV-m. The non-woven fabric filter
that was initially used was organic, so
there was a limit to the improvement inperformance even if the amount ofphotocatalyst loaded was increased. Afilter made of inorganic material was used,and by applying appropriate pretreatment,a significant improvement in performance
was achieved.

A solution containing bacteriophage Q(was sprayed with a nebulizer in a 370 L
glove box to make an aerosols. At themeasurement time, 10 L air was sampledthrough a gelatin filter and the infectivity
was evaluated by the plaque method.

Although aerosols suspended in the
air for long time cannot be caught
by the rough filter, it was suggested
that the small droplet remover usinga photocatalyst can inactivate
viruses contained in aerosols.