Yonago Acta medica 2009;52:77–84

Indoor Air Quality of Tottori University Lecture Rooms andMeasures for Decreasing Carbon Dioxide Concentrations
Daisuke Houri, Yousuke Kanazawa*, Ikuharu Morioka† and Kenji Matsumoto*
Division of Medical Environmentology, Department of Social Medicine, School of Medicine,
Tottori University Faculty of Medicine, Yonago 683-8503, *Department of Regional Environment, Faculty of Regional Sciences, Tottori University, Tottori 680-8551 and †Wakayama Medical University School of Health and Nursing Science, Wakayama 641-0011 JapanTo make clear the realities of indoor air (IA) pollution in lecture rooms of Tottori University in Japan, we studied air quality by monitoring the CO2 level, an index of IA pollution.
We changed IA environment of lecture rooms while the lecture was given by using fanventilation or not, and with room doors open or closed: we monitored the CO2 level at
5-min intervals during 2 or 3 consecutive 90-min lectures using an infrared ray absorption
type CO2 monitor. Based on the observed levels for 90 min, we calculated the ventilation
rate (times of operating the ventilation fan), and estimated CO2 level change in ventilated
and non-ventilated rooms for a 90-min lecture with the ventilation rate. In non-ventilatedrooms, the observed and estimated CO2 level exceeded the maximum of 1,500 ppm specified by the Japanese Government. The excess was irrespective of the ratio of air volume/
person in non-ventilated rooms with doors closed. During the 1-h lunch break with doors
open, over 5,000 ppm levels dropped below the standard. During the lecture in fan-ventilation, the CO2 level was decreased to below or near above the standard. Fan-ventilation during the lecture break reduced the level nearly to that in the outside air. In the case of no
fan-ventilation during the following lecture(s), the level exceeded the standard. To maintain a clean air environment in highly airtight university lecture rooms, ventilation duringlectures was crucial, which can be done effectively by the use of ventilation fans. Use of theestimated level is generally adaptive in promoting the use of ventilation fans.
Key words: air quality; carbon dioxide; school environmental health; ventilation

Appropriate room ventilation is necessary to maintain an appropriate environment for IA or to decrease the level of toxic chemical substances.
In many elementary schools, window frames
in classroom doors and walls facing the hallway are
made of wood and poorly fitted, so that elementary
schools have no airtight rooms, and generally use
natural ventilation. In contrast, university lecturerooms with highly airtight steel-made doors areequipped with ventilation fans and depend on artificial ventilation. In Japan, however, we have no

Cause of the sick building syndrome are mainly
linked with the trend of making highly insulated
airtight houses, which lowers the amount of naturalventilation (Iwashita et al., 1997). As other causes,
generations of volatile organic compounds and formaldehyde were reported (Hays et al., 1995). The
key index of indoor air (IA) pollution is the CO2
concentration. If the indoor CO2 level is high, therisk of the sick building syndrome rises (Gupta
et al., 2007). The degree of contamination of IA
quality can be evaluated by measuring CO2 levels.
Abbreviation: IA, indoor air

77

D. Houri et al.

Table 1. Characteristics and usage of monitored rooms with CO2 levels at monitoring start
Room X

Room Y

224
48

216
81

(m3

Room volume)
Seating capacity		
Ventilation fan
CO2 at monitoring start
Ventilation rate

(ppm)
(times/h)

Not operated
408
1.0

Operated437
7.0

Number of people in the room
Period 2			Period 3			Period 4
24 [9.3]
25 [9.0]
Period 5
24 [9.3]
25 [9.0]
Monitored day (2007)
12 Dec.
19 Dec.

Not operated
497
0.7

Operated471
5.0

64 [3.4]
60 [3.6]
55 [3.9]52 [4.2]
14 Dec.

59 [3.7]
60 [3.6]
60 [3.6]
55 [3.9]21 Dec.

[ ], ratio of air volume/person in m3/h/person.

riods 2 to 5 on 14 Dec. 2007 in Room Y (Tottori
University Faculty of Engineering). We chosen
Rooms X and Y, because the rooms were consecutively used for 2 periods or longer at that timeof the year, because the rooms could hold students
to the rooms’ full capacity and because the rooms
were newly installed with total heat exchange typeventilation fans after rebuilding in 2003. CO2
levels in ventilation were monitored in the samerooms at the same Periods 1 week later.
The volume and seating capacity of lecturerooms are described in Table 1. The openness orcloseness of room doors and fan-ventilating or noton the monitored days were also recorded. Indoor and outdoor temperatures were continuously
measured with a temperature humidity data logger(TH-101, Micro Techno, Kawasaki, Japan). The
indoor temperature was measured at the same sites
as the CO2 level was monitored, and the outdoor
temperature, on the outside stairs on the 2nd floorof the Faculty of Regional Sciences building.

standardized regulation in fan-ventilating: ventilation is not especially recommended, and the operation is left up to room users. The frequency of IA
pollution increases in summer and winter, becauseof the above-noted few ventilation times partly tosave energy and to maintain air-conditioned effects.
In addition, the IA pollution occurs more easilyin school than in office because of the population
density (Clements-Croome et al., 2008). Because
no major problems arise as a result of ignoring air
quality, this tends to be forgotten as an important
aspect of school life (Griffiths and Eftekhari, 2008).
The air quality has been studied on elementary
schools and residential houses (Shaughnessy et al.,2006; Kinshella et al., 2001), but little on university
lecture rooms, due to the difference in ventilation
methods and air volume. From the viewpoint ofstudy and health for university students, we investigated IA pollution in Tottori University lecturerooms by measuring CO2 levels continuously, anddiscussed possible countermeasures to deal withobserved problems.

CO2 level monitoring
Materials and Methods

An infrared absorption type CO2 monitor (Telaire
7001, Onset Computer, Pocasset, MA) (measuring
range: 0–10,000 ppm, accuracy: ± 50 ppm) was set
up at desk-top height in the center of each room,and the CO2 level was continuously monitored at intervals of 5 min throughout the period. CO2 levelsin the rooms before the monitoring start had been

Measurement sites
CO2 levels in non-ventilation were monitored in
Periods 4 and 5 on 12 Dec. 2007 in Room X (Tottori
University Faculty of Agriculture) and from Pe78

Air quality and CO2 concentration

raised because of the previous lecture use, and so
we started monitoring after CO2 levels fell to about
450 ppm. Following the monitoring in the lecture
time, we continued monitoring until 9:00 AM on
the next day, and attenuated CO2 levels were used
to calculate the ventilation rate (times of operating
the ventilation fan) in after-school sealed rooms.

where C0, CO2 level of air entering from outside(%); C1, CO2 level of IA at a monitoring start (t = 0)(%); Ct, average CO2 level of IA after time t (%); E,
ventilation rate (times/h); M, amount of CO2 generated indoors (m3/h); t, elapsed time between a monitoring start and the next start (h); V, amount ofventilation (m3/h); VR, room volume (m3); Vt, total
amount of ventilation for time t (m3).

Calculation of the ventilation rate
Estimation of CO2 levels

The ventilation rate when the rooms were sealed
was calculated with the CO2 data observed fromthe lecture end to 9:00 AM on the next day, using
the formulae (1) and (2) noted below (Pharmaceutical Society of Japan, 2000): the ventilation
rate when the rooms were fan-ventilated, using
the formulae (2) and (3) (Pharmaceutical Societyof Japan, 2000). The ventilation fan we used ineach room was the total heat exchange ventilator
with the air amount set to low to avoid the running noise. The running noise was measured witha Sound Level Meter NA-20 (Rion, Tokyo, Japan)
at 30-min intervals for 5 min. The students were
given lectures on general education. Most were seated at the beginning of the lectures and sat quietly
during class. The number of people in a room was
not changed excepting a few latecomers and those
who left early. We assumed the number of people
in the room or metabolic rate not changed, andanalyzed the CO2 level generated by students themselves, with reference to the “Standards for School
Environmental Sanitation” (0.022 m3/h) (Ministryof Education, Culture, Sports, Science and Technology of Japan, 2004).

To make clear the CO2 level change during a lecture over 90 min, we calculated the estimated levels
with the formulae (4) and (5) (Pharmaceutical Society of Japan, 2000), at 5-min intervals according to
the ventilation rate in ventilated or non-ventilatedrooms.

Results
Table 1 shows fan-ventilating conditions, CO2 levels, number of people in the room and ratio of air
volume/person classified by room.
Usage of Room X on monitored days
Figure 1-I shows the schema of Room X, where wemonitored during Periods 4 and 5. The lecture on
monitored days took 2 full periods, and no students
entered or left as the lecture went on: breaks between lectures were different from the usual. On
12 Dec. when Room X was not ventilated, the lecture break was from 16:35 to 16:45: this class wasa laboratory class, and doors were often opened
and closed. On 19 Dec. when Room X was ventilated, the lecture ended at 16:40 without break.

V = 2.303 VR log C1 – C0 ………… (1)tCt – C0
E = V
VR……………………………… (2)Level change in Room X

M 100
V =
Ct – C0
Vt = VRt………………………… (3)E

Figure 2 shows changes in non-ventilated Room X(12 Dec.) and ventilated Room X (19 Dec.). This
figure also shows openness or closeness of room
doors, and ventilation or non-ventilation in doorway areas. Indoor CO2 levels at the monitoring……………………… (4)Ct = C0 + (l – e–Et) M

100
Vt………… (5)79D. Houri et al.

start were 408 ppm on 12 Dec. and 437 ppm on 19
Dec. (Table 1). On 12 Dec., the CO2 level in nonventilated Room X began to rise from the lecture
start (14:40), exceeded 1,500 ppm at 15:15 and continued to rise. It dropped slightly during the break(16:35–16:45), but rose to 3,070 ppm at 17:20 when
the laboratory class began. Thereafter, the level
decreased in doorway areas as students frequently
entered or left. At 17:50 when the class ended on
12 Dec., the level was 2,154 ppm and the outdoor
CO2 level was 398 ppm. On 19 Dec., the CO2 levelin ventilated Room X rose from the lecture start(14:40), and reached 883 ppm 10 min later. By thelecture end (16:45), the level had increased by 750
ppm but did not exceed 1,500 ppm. The outdoor
CO2 level on 19 Dec. was 403 ppm. The ventilation rate was 1.0 time/h for after-school sealed
Room X and 7.0 times/h for ventilated Room X(Table 2).
Usage of Room Y on monitored days
Figure 1-II is the schema of Room Y. During Periods 2 to 5, CO2 levels were monitored in nonventilation on 14 Dec. and in ventilation on 21 Dec.
There were about 60 people on both days (Table 1).
During the lunch break, 4 to 20 people seated between 12:00 and 12:40, and about 20 to 60 people
between 12:40 and 13:00.

Fig. 1. Schemas of lecture rooms. I: Faculty of Agriculture
Room X. II: Faculty of Engineering Room Y. DW,
doorway; VF, ventilation fan; VFI, VF inlet; VFO, VF outlet; Win, window.

Level change in Room Y
(ppm)
4000

Figure 3 shows changes in Room Y on 14 Dec.
when the room was not ventilated and on 21
Dec. when it was ventilated. Figure 3 also showschanges when the doors were open or closed, withventilation or non-ventilation in doorway areas.
The indoor level in non-ventilated Room Y was
497 ppm at 10:05 when the monitoring was started(Table 1). The students enterd the room immediately after the monitoring start. At 10:30, the levelexceeded 1,500 ppm, and at 11:50 (end of Period2) reached 5,248 ppm. During the lunch break(11:50–13:00), Doorways 1 and 2 were opened,
and the level was quickly dropped to 1,144 ppm.
At 13:00, Period 3 began and the level rose again,

Period 5

Period 4

3000

A

2000
1000
0

14:00

B
15:00

16:00

17:00

A
B
14:00

18:00 (time)

DW 1
DW 2
DW 2
VF
15:00

16:00

17:00

18:00

Fig. 2. Changes in CO2 levels monitored in Room X. A:
not fan-ventilated. B: fan-ventilated.
: fan-ventilatedwith doors open. DW, doorway; VF, ventilation fan.

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Air quality and CO2 concentration

Table 2. Ventilation rate and room ventilation

and at 14:30 (end of Period 3) reached 5,036 ppm.
Between 14:30 and 14:40 (break between Periods 3
and 4), Doorways 1 and 2 were opened. Till 14:50
Doorway 2 remained open even after the start ofPeriod 4, and the level decreased to 3,273 ppm.
However, once Doorway 2 was closed, at 16:05 (endof Period 4) it rose again to 5,312 ppm. Between
16:20 and 16:30, after Period 5 began, Window
2 was 25% open, and the level rise was slowed.
Once Window 2 was closed, the level increase
became more rapid, and at 17:40 (end of Period 5)
reached 6,276 ppm. Between 17:40 and 17:55 (endof monitoring), Doorways 1 and 2 were intentionally opened, and the level was decreased to 2,601
ppm.
The indoor level in ventilated Room Y was
471 ppm at 10:05 when the monitoring was started(Table 1). From 10:15, the level began to rise as
the number of people in Room Y increased, andat 10:40 reached 1,653 ppm. By 11:50, the levelchanged to about 1,600 ppm (end of Period 2).
During the lunch break, Doorways 1 and 2 wereopened, and the level dropped to 1,100 ppm. At
13:00 (start of Period 3), Doorways 1 and 2 wereclosed, and by 14:25 the level reached 1700 ppm(end of Period 3). From 14:40 (start of Period 4),

Ventilation rate (times/h)Room X
Room Y
Observed in non-ventilation
Observed in ventilation
Estimated by the formulae

1.0
7.0
2.2

0.7
5.0 [8.7]
5.6[ ], at Doorway 2.

Doorway 2 was open, and the level was decreased
to about 1,050 ppm. Between 15:45 and 16:10, thelevel was further decreased to 650 ppm because
the sources of CO2, students and teacher, moved toanother room and were gone. From 16:20, ventilation was stopped for Period 5. But by 17:55 (endof monitoring), the level was changed to 1,100
ppm, because Doorway 2 was open. We calculated the ventilation rate in Room Y as 0.7 time/hin non-ventilation, 5.0 times/h in ventilation and8.7 times/h in ventilation with Doorway-2 open
(Table 2).
Change in estimated levels
We figured changes in the presently observed andtheoretically estimated CO2 levels during the lec-

Fig. 3. Changes in CO2 levels monitored in Room Y. A: not fan-ventilated. B: fan-ventilated.
doors open. DW, doorway; VF, ventilation fan; Win, window.

81: fan-ventilated with

D. Houri et al.

ture time over 90 min by room. The levels werebased on the ventilation rates at 5-min intervals inventilated and non-ventilated rooms (Fig. 4). The
estimated value in non-ventilation at the end of
the 90-min lecture was 6,075 ppm in Room Y and2,307 ppm in Room X; while the observed value,
5,248 ppm in Room Y and 2,513 ppm in Room X.
The estimated value in ventilated Room X fluctuated around 750 ppm 20 min after the lecture start,
and was still 750 ppm 90 min later. The estimatedvalue in ventilated Room Y fluctuated around 1,600
ppm 20 min after the lecture start, and was 1,621
ppm 90 min later.
Noise level
In non-ventilation, the noise level was 38 to 40 dB
in Room X and 36 to 38 dB in Room Y. In ventilation, the noise level was 40 to 42 dB in Room X
and 38 to 40 dB in Room Y.

Discussion
Fig. 4. Observed and estimated CO2 levels in ventilated andnon-ventilated Rooms X and Y. Room conditions for calculating estimated values were 0.022 m3/h/person, 400 ppm as
CO2 of the indoor air at the monitoring start and 400 ppm as
CO2 of the air entering from outside.

In 2002, the Ministry of Education, Culture,
Sports, Science and Technology of Japan determined the standards for school indoor chemical
substance density by revising the Standards forEnvironmental Hygiene in School (Ministry of
Education, Culture, Sports, Science and Technology of Japan, 2002). The 2002 revision has recommended air quality control by checking the CO2
density and ventilation rate twice a year. Most
school classrooms in Japan have natural ventilation. The revision demands 0.15% (1,500 ppm) or
less as the preferable level, and fixes standard ventilation times for classrooms. On the other hand in1970, the Ministry of Health, Labour and Welfareof Japan established CO2 standards for keeping
contaminants (CO2, formaldehydes and suspended
particles) below standards, 0.1% (1000 ppm) by theLaw for Maintenance of Sanitation in Buildings(Japanese Government, 1970): the Law stipulates
evaluation of IA quality and degree of IA pollution.
The above standards are for the overall index of
IA quality, not based on CO2 effects on health, but

based on increase of other contaminants estimatedto be in parallel with the increase of CO2 over 1,000
ppm. Indoor CO2 is increased by students’ exhaledair. When the indoor level is high, it is assumed
that the room is not ventilated. As the result of
non-ventilation, oxygen is decreased, suspended
particles are increased, bacteria are increased andbody odor gets severer for students to be annoyed
about unpleasant smells (Takahashi, 1982; Ministryof Education, Culture, Sports, Science and Technology of Japan, 2004). On the other hand, 5,000
ppm has been determined as a permissible level by
the Japan Association of Industrial Health and theAmerican Conference of Governmental Industrial
Hygienists (Araki, 1990; American Conference ofGovernmental Industrial Hygienists, 2007). The
CO2 level observed in the non-ventilated rooms far
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Air quality and CO2 concentration

to keep IA clean, it is important to ventilate the lecture room during the lecture. The estimated levels
were higher for Room Y than Room X both in ventilation and non-ventilation, presumably because
the number of students in Room X was smaller
than Room Y. The estimated levels higher than theobserved in non-ventilated Room Y may be caused
by ventilation taking place in Room Y by the openings and closings of doors.
The CO2 level in ventilated rooms with doors
closed was kept below the standard of 1,500 ppm
in Room X, and slightly higher than the standard
in Room Y. In considering these facts, ventilationof rooms can keep the CO2 level below or near the
standard, by which IA pollution would be reduced.
The shift of estimated levels in ventilated rooms
was similar to that of the observed, keeping below
or slightly higher than the standard. In keeping IA
clean in highly airtight university lecture rooms, it
is important to ventilate the room during lecture by
opening classroom doorways or by fan-ventilating.
We observed that ventilation through opening
doors had a large effect. However, opening doors
introduces outside air directly indoors, and no temperature or amount of wind of the inflowing air canbe controlled. We did not investigate the influenceof opening doors on indoor thermal environment in
the present study. We cannot expect that opening
doors keep the environment within the comfortable
range. Furthermore, when rooms are air-conditioned in summer and winter, ventilation by opening doors is not preferable also from the energysaving aspect.
In contrast, ventilation by using ventilationfans can ensure a constant amount of ventilation.
Accordingly, in the present study, we observed no
rapid level change, but little change below the standard or near above. In the case of using ventilationfans, however, the influence on the indoor temperature and the amount of running noise will arouseconcern. In the present study, the heat temperature
setting for lecture rooms was fixed, and we could
not confirm effects of ventilation on the thermal
environment. By the way, the heat exchange typeventilation fan we used here can supply outside air

exceeded 1,500 ppm, the limit determined at the“Standards for School Environmental Sanitation”.
Sometimes the level exceeded 3,000 ppm in RoomX and 6,000 ppm in Room Y.
The CO2 level, an index of IA quality, is influenced by the ratio of air volume/person and ventilation rate. The ratio of air volume/person was
higher in Room X than Room Y. Accordingly, theCO2 level in non-ventilated Room X should havebeen lower than in non-ventilated Room Y. However, in the case of no ventilation, the level was
kept above the standard in either room. We thinkthat the highness was due to the sealed nature of
the room during leture: the doorways were open
only when the teacher and students entered forclass or exit after class, as in the same way during
the break. Moreover, room doors were opened
during the break for coming-in and going-out ofstudents, and open-door ventilation decreased thehigh CO2 level. When doors were kept open in
Room Y between 12:00 and 13:00, over 5,000 ppm
CO2 was decreased to below the standard. The effect of natural ventilation by opening room doors
impacted.
As observed, when rooms were not ventilated,
CO2 attained a high density, and we fully realized
the need of fan-ventilation. It is preferable to measure by every room to know actual conditions, but
we cannot monitor many rooms with the present
method. This is the reason we tried to estimate themeasurements using the theoretical formulae. The
estimated level as well as the observed level exceeded the standard of 1,500 ppm in non-ventilatedrooms. The final CO2 level differed according to
the ratio of air volume/person; however, when thelecture room was sealed over 90 min, it was difficult to keep the level below standard regardless of
air volume. In estimating and observing the levels,
we started by setting the the initial indoor level as
400 and 450 ppm, respectively. But, both levels
exceeded the standard within 90 min. Even if theCO2 level was adjusted to below the standard during a break, in the case of no ventilation during a
lecture, IA quality must be negatively affected andhigh-level air pollution would result. Accordingly,
83

D. Houri et al.

by exchanging the temperature close to the room
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because the noise met the standard of 50 dB or lessdetermined by the “Standards for School Environmental Sanitation”.

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Received September 4, 2008; accepted March 31, 2009
Corresponding author: Daisuke Houri, PhD

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