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The on-board carbon dioxide concentrations and ventilation performance in passenger cabins of US domestic flights

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The on-board carbon dioxide concentrations and ventilation performance in passenger cabins of US domestic flights

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Billions of people travel on airplanes every year, making the aircraft cabin a critical environment to understand with regard to public health. The main control over indoor environmental quality in the cabin is ventilation; therefore, maintaining sufficient ventilation rates on-board is essential for creating healthy and comfortable cabin environments. We measured real-time CO2 concentrations, an indicator of ventilation rates, and cabin pressure in the passenger cabins of 179 US domestic flights from boarding through deplaning. The average CO2 concentrations were 1353 ± 290 ppmv (mean ± SD) and the estimated outside airflow rates were 5.77 ± 2.09 L/s/p across all flights. The results indicated that 96% of observations met the minimum recommended outside airflow rates for acceptable air quality (3.5 L/s/p), but only 73% met the rate required in FAA design requirements (4.7 L/s/p), during flying phases. The CO2 levels on all flights were well below the occupational exposure limit of 5000 ppmv. Statistical analysis indicated that the ventilation rates during boarding phases were significantly lower than the others. The findings are of particular interest because low ventilation in other settings has been associated with increased rates of disease transmission, increased upper respiratory symptoms, and worse performance on cognitive function tests. Verification of ventilation performance rather than reliance on design estimates for determining compliance with ventilation standards is recommended.
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Original Paper
I
Indoor
and
and B
uilt
uilt
Environment
The on-board carbon dioxide
concentrations and ventilation
performance in passenger cabins
of US domestic flights
Xiaodong Cao
1
, Christopher D. Zevitas
2
,
John D. Spengler
1
, Brent Coull
3
, Eileen McNeely
1
,
Byron Jones
4
, Sin Ming Loo
5
, Piers MacNaughton
1
and
Joseph G. Allen
1
Abstract
Billions of people travel on airplanes every year, making the aircraft cabin a critical environment to
understand with regard to public health. The main control over indoor environmental quality in the
cabin is ventilation; therefore, maintaining sufficient ventilation rates on-board is essential for creating
healthy and comfortable cabin environments. We measured real-time CO
2
concentrations, an indicator
of ventilation rates, and cabin pressure in the passenger cabins of 179 US domestic flights from board-
ing through deplaning. The average CO
2
concentrations were 1353 290 ppmv (mean SD) and the
estimated outside airflow rates were 5.77 2.09 L/s/p across all flights. The results indicated that 96% of
observations met the minimum recommended outside airflow rates for acceptable air quality (3.5 L/s/p),
but only 73% met the rate required in FAA design requirements (4.7 L/s/p), during flying phases. The CO
2
levels on all flights were well below the occupational exposure limit of 5000 ppmv. Statistical analysis
indicated that the ventilation rates during boarding phases were significantly lower than the others. The
findings are of particular interest because low ventilation in other settings has been associated with
increased rates of disease transmission, increased upper respiratory symptoms, and worse perfor-
mance on cognitive function tests. Verification of ventilation performance rather than reliance on
design estimates for determining compliance with ventilation standards is recommended.
Keywords
Aircraft cabin, Ventilation, Carbon dioxide, Airflow rate, Air quality
Accepted 20 July 2018
Introduction
The International Air Transport Association (IATA)
expects 7.2 billion passengers to travel in 2035, a near
doubling of the 3.8 billion air travellers in 2016, with a
3.7% annual Compound Average Growth Rate.
1
Transformational changes are underway, especially in
Asia and the Middle East where aviation growth is
expected to be even greater. Airplane cabin air quality
has received considerable attention. Several studies
have highlighted the in-flight transmission of infectious
disease, such as SARS, tuberculosis, common cold and
norovirus.
2–5
Other studies have focused on chemical
1
Department of Environmental Health, Harvard T.H. Chan
School of Public Health, Boston, MA, USA
2
U.S. Department of Transportation, Volpe National
Transportation Systems Center, Cambridge, MA, USA
3
Department of Biostatistics, Harvard T.H. Chan School of
Public Health, Boston, MA, USA
4
College of Engineering, Kansas State University, Manhattan,
KS, USA
5
Department of Electrical and Computer Engineering, Boise
State University, Boise, ID, USA
Corresponding author:
Joseph G. Allen, Department of Environmental Health, Harvard
T.H. Chan School of Public Health, 401 Park Drive, Boston
02215, MA, USA.
Email: jgallen@hsph.harvard.edu
Indoor and Built Environment
0(0) 1–11
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stressors inside the cabin, including flame retardants,
6,7
ozone,
8–10
VOCs
11,12
and particulate matter (PM).
13,14
The aircraft cabin is a unique environment that
relies on an aircraft environmental control system
(ECS) to move passengers and crew through an exter-
nal environment widely variable in temperature (80 to
>50C), pressure (10.1–101 kPa), and relative humidity
(near dry to saturation).
15
Air supplied to the aircraft
cabin is a combination of outside air brought in from
engines (bleed air) and air removed from the cabin,
which is filtered and recirculated. At the ECS terminal,
a mixing air distribution system regulates the cabin air
velocity/temperature, relative humidity and provides
sufficient fresh air to dilute gaseous and particulate
contaminants. Therefore, ventilation plays a key role
in maintaining a safe, healthy and comfort cabin envi-
ronment, by conditioning outdoor air, and controlling
in-cabin pollutants’ concentrations.
Ventilation standards for the aircraft cabin condi-
tions vary by country. In the USA, the airline industry
is regulated by the Federal Aviation Administration
(FAA). The FAA has established Federal Aviation
Regulations (FAR) to guide the operation of commer-
cial airliners. FAR 14 CFR 25.831
16
states that the
cabin ventilation system must provide at least 0.55 lb
(0.25 kg) of fresh air for each passenger per minute,
equivalent to 4.7 L/s/p at 8000 feet (2438 m) altitude
and cabin temperature of 22C (72F). This ventilation
rate is also specified by the joint design regulation
FAR/JAR Part 25
16
for crew members to perform
their duties without undue discomfort or fatigue and
to provide reasonable passenger comfort. It should be
noted that FAA only certifies performance based on
the design of aircraft ventilation system, not the
actual ventilation performance. US airlines are not
required to certify compliance through routine direct
monitoring or audits. As noted in a National Research
Council (NRC) report,
15
established FARs may be
inadequate to protect the health of the flight crew
and passengers.
In addition to federal regulations for minimum ven-
tilation rates, ASHRAE issued the ANSI/ASHRAE
standard 161–2007
17
for specifying requirements for
air quality within commercial aircraft. This standard
specifies a minimum outside air ventilation rate of 3.5
L/s/p. Further, a total air supply (mixture of outside air
and recirculated air) rate of 7.1 L/s/p should be the
minimum, and a rate of 9.4 L/s/p is recommended.
When the supply air is from the on-board systems
(i.e. the auxiliary power unit (APU) or engine bleed
air), the standard requires a minimum of 3.5 L/s/p of
outdoor air. However, if the source of supply air is
from the airport terminal or ground carts, then the
ventilation rate of 9.4 L/s/p of total air is required.
CO
2
concentration has long been used as a proxy for
ventilation,
18
using CO
2
exhaled by passengers as a
tracer gas, and as an indicator of environments that
occupants will find unsatisfactory. ASHRAE standard
62.1–2013
19
references CO
2
with respect to odour per-
ception. It states that indoor CO
2
concentrations no
greater than 700 parts per million by volume (ppmv)
above outdoor CO
2
levels in typical office buildings is
an indicator that visitors entering the space will be sat-
isfied with respect to human bioeffluents (body odour).
In addition to its use as a proxy for ventilation and
satisfaction, recent evidence suggests that CO
2
may
also be a direct pollutant. Hypercapnia (CO
2
retention)
stimulates vasodilation of cerebral blood vessels,
increasing cerebral blood flow and elevating intracra-
nial pressure, which can cause dyspnea on exertion,
headaches, visual disturbance, impaired cognitive func-
tion, and other central nervous system symptoms.
20
A recent study
20
in the space station indicated that ele-
vated CO
2
can lead to symptoms such as headache and
lethargy. Other studies found that the exposure to CO
2
at concentrations typically encountered in indoor envi-
ronments (950–2500 ppm) is associated with decre-
ments in human cognitive function.
21–24
These
impacts were observed at concentrations well below
the 5000 ppmv exposure limit set by Occupational
Safety and Health Administration (OSHA).
25
Investigation of ventilation performance in aircraft
cabin can use simulated environment chamber. Cao
et al.
26–28
used a large-scale particle image velocimetry
(PIV) system to study the air distributions in a Boeing
737 cabin mockup occupied by 42 heating manikins.
They found that the cabin airflows were at low velocity
and high turbulence levels. The low-speed air motion
may lead to poor ventilation effectiveness in the pas-
senger zone, even at a total ventilation rate of 9.4 L/s/p,
as recommended by ASHRAE. Du et al.
29
experimen-
tally studied the jet flow characteristics from a ventila-
tion nozzle in an aircraft cabin mockup. They
concluded that the effect of nozzle jet on passenger’s
thermal comfort was mostly affected by air velocity
distribution. Wang et al.
30
studied the ventilation per-
formance in a Boeing 767 cabin mockup containing 35
manikins. The CO
2
released by manikins was used as a
tracer gas to evaluate the air exchange rate and venti-
lation effectiveness in the breathing zone of passengers.
They found that the local mean age of air decreased
almost linearly with an increase in fresh air supply
rates. Strøm-Tejsen et al.
31
used a 21-seat cabin
mockup with realistic pollution sources to investigate
the balance between fresh air and humidity during a
simulated 7-h flight. The study covered four conditions
of outside airflow rate ranged from 1.4 to 9.4 L/s per
person. Sixty-eight subjects acting as passengers were
exposed to the four simulated flight conditions.
2Indoor and Built Environment 0(0)
The results showed that the reduced outside air could
intensify the symptoms commonly associated with air
travel (headache, dizziness and claustrophobia). These
studies provided comprehensive evaluation of the ven-
tilation performance in controlled cabin environments
and simulated conditions.
Some researchers have further performed on-board
measurements of ventilation on actual flights. Spengler
et al.
32
conducted environmental monitoring in the pas-
senger cabin of 83 commercial flights, including six air-
craft types (2 Airbus and 4 Boeing), flying US domestic
and international routes. Various environmental
parameters were monitored including CO
2
, particles,
ozone, volatile organic compounds (VOCs) and noise.
They found that the ventilation rates on high-passenger
load flights could be below the required 3.5 L/s/p, as
indicated by high CO
2
concentrations. The concentra-
tions of some passenger-related VOCs were also higher
for flights with reduced ventilation rates. The air qual-
ity inside cabins of Boeing 747, A330 and A340 air-
crafts were investigated by Lee et al.
33
on 16 flights.
The measured CO
2
concentrations were well below
the OSHA exposure limit but exceeded the recom-
mended value by ASHRAE standard 62.1 (about
1000 ppmv), ranging from 2000 to 2500 ppmv.
Twenty one percent of the crew considered that the
air quality was poor during the flight. Similarly, a
study of 43 flights on commercial airlines showed that
the levels of CO
2
on most flights were higher than that
recommended by the ASHRAE Standard 62.
34
Li
et al.
13
and Guan et al.
11
conducted on-board measure-
ments in the passenger cabin of Boeing 737–800 aircraft
on a few domestic flights. CO
2
concentrations were also
recorded to calculate the outside air ventilation rates,
which were then used to identify contributions of air-
borne particles and VOCs from outside and inside the
cabin. The results showed that the outside airflows on
all tested flights were within relevant aircraft cabin ven-
tilation standards limits. For PM, contributions from
the bleed air and cabin interior were both important.
On the contrary, around 90% of VOCs came from
emissions inside the cabin.
Considering the vast numbers of flights that occur
annually on a global basis, the extent of actual meas-
urements on airplanes is quite limited. Further, com-
parison of on-board ventilation performance to
regulations and standards has not been fully explored.
Lastly, little is known about ventilation and the vari-
ability of carbon dioxide throughout the entire flight
experience, and whether there may be critical periods
with inadequate ventilation. Therefore, the overall
objectives of this study were to: (1) characterize the
variability of carbon dioxide throughout all phases of
flight, and (2) estimate ventilation during the whole
flight using CO
2
as a proxy for ventilation.
Methods
Flight information
On-board monitoring was conducted on a total of 179
US domestic flights from 10 July 2007 to 13 September
2009. The flights covered 24 aircraft types, 7 aircraft
series, 10 airlines and 58 flight routes. The largest pro-
portion of aircraft types were the Boeing 757 and MD-
88 models, accounting for 37% and 30% of all tested
flights, respectively. Most of the investigated aircraft
models are short- to medium-range narrow-body
twin-engine jet airliners (see Table 1), which are com-
monly used for domestic airline services. In these air-
liners, the conditioned air was delivered by means of
diffusers placed high in the cabin, and returned
through grilles at bottom sides of the cabin. The
median sampling duration was 1 h 14 min.
On-board measurement
We measured CO
2
concentrations and cabin pressure
using a modular and portable sensing package devel-
oped by Boise State University, known as the
ASCENT 1000.
35
The ASCENT 1000 package was
fixed to the seatback pocket or was placed on the
tray table to measure CO
2
concentrations in re-
circulated air, which could represent the average CO
2
level in the cabin under the fully mixing condition. The
seat locations varied from flight to flight, mostly in
economy cabins (only two tests performed in first-
class cabins). The cabin pressure and CO
2
concentra-
tions were recorded at intervals of either 10, 30 or 60 s.
The ASCENT 1000 passed tests for electromagnetic
interference by the Boeing Company and was approved
for use on commercial flights. The ASCENT 1000
package was pre-calibrated and tested in six flights by
Loo et al.
35
Inside the package, pressure sensing
was accomplished by a VTI Technologies SCP1000
sensor module with a measuring range of 30–120 kPa
(200 Pa). CO
2
concentrations were determined using
a Telaire 6004 CO
2
OEM sensor (General Electricity
Company). The measured CO
2
concentrations were
automatically corrected to compensate for air pressure
changes. This adjustment was done in real-time by the
sensor once it received the pressure measurement. The
sensor had a calibrated detection range of 0 to 2000
ppmv (40 ppmv or 3% of readings, whichever is
greater). The narrower range could provide a better
accuracy for lower levels more likely to be encountered
in aircraft cabins. In this study, 98% of measured CO
2
concentrations were within this range. The sensor could
detect concentrations above 2000 ppmv but with lower
measurement accuracy.
Cao et al. 3
The whole flight was divided into five phases: board-
ing, ascent, cruise, descent and deplaning. The flight
phases could be clearly distinguished by changes of
cabin pressure. Boarding phase was defined as a
period of constant cabin pressure prior to take-off.
Measurement campaign typically began when most or
all the passengers have boarded. So, the boarding
phase included a fraction of boarding process and
whole taxiing process. Ascent phase was a period char-
acterized by a steady decline in cabin pressure after
take-off until a constant pressure was achieved at
cruise phase. Descent phase was a period of steady
increase in cabin pressure after the cruise phase. After
landing, the cabin pressure became constant again
during deplaning phase. The pressure and CO
2
data
were continuously monitored from ascent to descent
on most flights. However, the measurement could not
be performed during boarding or deplaning phases on
some flights due to operational restrictions.
Estimation of outside airflow rate
The transient in-cabin/ambient CO
2
concentrations,
outside airflow rate and generation rate of CO
2
per
person together follow equation (1)
11,13,36
under the
fully mixed approximation
VdCi;j
dt 103¼NQjCo;j106
NQjCi;j106þNG
3600
(1)
where Q
j
¼outside airflow rate at time j(L/s/p);
G¼average CO
2
generation rate by a person (L/hr);
C
i,j
¼CO
2
concentration inside the cabin at time
point j(ppmv); C
o,j
¼CO
2
concentration outside the
cabin at time point j(ppmv); N¼number of passen-
gers; V¼cabin volume (m
3
); t¼time (s).
Based on this formula, the outside air ventilation
rates can be estimated using measured CO
2
concentra-
tions and a steady-state approximation, also known as
the constant concentration method. This method
assumes that the in-cabin CO
2
concentration is steady
during each measuring period, and the dominant
source of CO
2
is the exhaled breath by passengers at
an average generation rate. The constant concentration
method has been successfully applied in several studies
on in-flight ventilation performance.
11,13,32,37
Because
of the high number of air changes per hour on
Table 1. Measured CO
2
concentrations and estimated outside airflow rates on all the flights.
Aircraft series
Aircraft
types
Aircraft
numbers
CO
2
concentration (ppmv) Outside ventilation rate (L/s/p)
Min Max Mean Median SD Min Max Mean Median SD
Airbus 319/320 A319 2 1003 1635 1228 1211 112 4.05 8.19 6.11 6.13 0.82
A320 3 682 2990 1175 1235 382 1.94 17.08 8.15 5.95 4.04
Boeing 737 B737-300 4 1032 1773 1479 1497 111 3.64 7.83 4.68 4.55 0.54
B737-400 1 1656 1937 1808 1804 65 3.26 3.98 3.56 3.57 0.16
B737-500 1 1000 1220 1124 1142 49 6.06 8.23 6.88 6.69 0.49
B737-700 7 850 2947 1261 1272 188 1.97 10.90 6.05 5.71 1.40
B737-800 6 661 2976 1288 1355 316 1.95 18.38 6.73 5.22 3.62
Boeing 757 B757 67 703 2992 1438 1421 284 1.94 15.95 5.19 4.88 1.52
Boeing 767 B767-300 5 756 1662 1234 1238 160 3.96 13.66 6.25 5.93 1.65
Bombardier CR-7 1 1094 2209 1903 1911 160 2.77 7.14 3.38 3.32 0.48
CR-9 5 658 2616 1451 1427 265 2.27 18.59 5.04 4.86 1.32
CRJ-100 2 620 1620 889 878 160 4.10 21.60 10.61 10.25 2.91
CRJ-140 1 1264 1566 1398 1384 79 4.28 5.76 5.02 5.07 0.39
CRJ-150 1 793 1233 969 976 127 5.97 12.42 9.07 8.58 1.88
CRJ-200 2 721 1442 1070 1049 173 4.79 15.09 7.90 7.63 2.14
Embraer E-135 1 1143 2077 1417 1381 185 2.99 6.68 5.04 5.08 0.79
E-145 1 682 2054 1201 1070 403 3.03 17.08 7.86 7.40 3.85
E-170 1 855 1352 1097 1083 160 5.23 10.78 7.49 7.25 1.73
E-175 8 686 2137 1162 1120 200 2.89 16.85 6.91 6.89 1.69
E-190 1 1392 2340 1771 1717 233 2.59 5.03 3.75 3.80 0.60
MD DC-9 3 934 1951 1340 1159 320 3.23 9.23 5.82 6.54 1.59
MD-80 1 659 1094 897 891 111 7.14 18.52 10.41 10.01 2.45
MD-88 53 514 2979 1321 1318 264 1.95 39.50 5.89 5.42 1.98
MD-90 2 656 2993 1251 1265 416 1.94 18.72 6.97 5.75 2.83
Summary 179 514 2993 1353 1333 290 1.94 39.50 5.77 5.34 2.09
4Indoor and Built Environment 0(0)
airplanes, steady-state conditions are reached more
rapidly than other indoor environments. Under the
steady-state condition, the left side of equation (1)
becomes 0, so the outside airflow rate can be estimated
by equation (2)
Qj¼106G
3600 Ci;jCo;j
ðÞ (2)
If the CO
2
concentration is changing rapidly, equa-
tion (2) will not be accurate due to the transient term in
equation (1). A simple order of magnitude assessment
showed that rates of change greater than about
1000 ppm/h may adversely impact the accuracy of the
ventilation rate calculated using the steady-state
approximation. This requirement typically will not be
met in the beginning of the boarding phase when the
concentration rises rapidly as large numbers of people
enter the aircraft. Even though equation (2) may not
give an accurate measure of the actual instantaneous
value of outside air being supplied to the cabin during
rapid transients in concentrations, the levels of CO
2
in
the air are indicative of contaminant levels in the air.
Consequently, the ventilation rates calculated with
equation (2) during transient periods may be consid-
ered as equivalent steady-state ventilation rates during
each measuring period and should be viewed in that
perspective.
The CO
2
concentration in the atmosphere generally
ranges from 365 ppmv to 390 ppmv, summarized by Li
et al.
13
Here, we used a mean outdoor CO
2
concentra-
tion of 386 ppmv, averaged from the global monthly
mean atmospheric CO
2
concentration data reported by
National Oceanic and Atmospheric Administration
(NOAA),
38
during the whole test period. The genera-
tion rate of CO
2
per person can be derived by
equation (3)
39
G¼RQð0:00276ADMÞ
0:23RQ þ0:77
ðÞ (3)
where RQ ¼respiratory quotient: 0.83 for an adult of
average size and engaged in sedentary activities;
39
M¼metabolic rate per unit surface area (METs);
A
D
¼DuBois surface area (m
2
), which can be calculat-
ed by equation (4) as
AD¼0:203H0:725W0:425 (4)
where H¼height (m) and W¼weight (kg).
The generation rates will vary for different people
depending on inputs in equations (3) and (4). Thus, a
Monte Carlo simulation was used to determine the
distribution of the CO
2
generation rate per person
from 100 air travellers.
32
The metabolic rate for each
passenger was selected using a uniform distribution in
the range of 0.9–1.3 METs, representing different phys-
ical active types from sleeping to sit/watch TV.
40
The
average generation rate of CO
2
per person from 10,000
simulation runs was 18.2 L/h.
Statistical analysis
Descriptive analysis was performed to show the mea-
sured CO
2
concentrations and estimated outside air-
flow rates by flight phases and aircraft types. Box
plots and probability distributions were used to com-
pare the data distributions by flight phases. Post-hoc
multiple comparisons using the Fisher’s least signifi-
cant difference (LSD) method
41
were performed to
test the influence of flight phases/duration on the ven-
tilation performance. A p-value <0.05 indicates a sta-
tistically significant difference for the mean value.
Results
Figure 1 depicts an example of the measured cabin
pressure and CO
2
concentrations during a typical
flight. As shown in Figure 1, the flight phases could
be clearly identified by changes in cabin pressure. The
FAR 14 CFR 25.831
16
states that the minimum cabin
pressure under normal operating conditions should not
be less than the pressure found at an altitude of 2438 m
(75.3 kPa), and all the tested flights met this standard.
This example highlights the typical variations in CO
2
concentration over the course of a flight. During the
boarding phase, the CO
2
concentrations increased rap-
idly, indicating low outside airflow rates. CO
2
concen-
trations decline steadily after taking-off and are lower,
but above levels typically acceptable in buildings (1000
ppmv) during the cruise and descent phases. Finally,
the CO
2
concentration increased again after landing.
The descriptive statistics of all measured CO
2
con-
centrations and corresponding outside air ventilation
rates by aircraft types are listed in Table 1. The CO
2
levels on all flights were well below the occupational
exposure limit of 5000 ppmv. Overall, across all aircraft
types and flight phases, the CO
2
concentrations varied
from 514 to 2993 ppmv, with an average value of 1353
290 ppmv (mean SD) and a median of 1333 ppmv.
Correspondingly, the outside airflow rates ranged from
1.94 to 39.50 L/s/p, and the average and median values
were 5.77 2.09 L/s/p and 5.34 L/s/p, respectively.
Figure 2 shows distributions of CO
2
concentrations
and corresponding outside airflow rates calculated
using equation (2) during each flight phase. Figure 2
(a) shows that CO
2
concentrations were the highest
during the boarding phase, with a median of 1539
Cao et al. 5
ppmv and an interquartile range (IQR) of 407 ppmv.
CO
2
levels during climbing were lower compared to
that during the boarding phase. The median CO
2
con-
centration was 1304 ppmv during cruise, the lowest
among all phases. During descent to deplaning, a grad-
ual increase in CO
2
levels was observed. The high CO
2
levels during the boarding phase indicated inadequate
ground ventilation by APU or gate-based ventilation
systems. As shown in Figure 2 (b), calculated ventila-
tion rate was significantly lower in the boarding phase
compared to all the other flight phases (p<0.0001),
with a median of 4.38 L/s/p (below the FAA regula-
tions) and an IQR of 1.84 L/s/p. The ventilation per-
formance gradually improved during ascent, and
reached a peak ventilation at the cruising phase, with
a median of 5.51 L/s/p and an IQR of 1.91 L/s/p.
Figure 3 depicts the percentages of in-cabin outside
airflow rates that met the two aircraft ventilation reg-
ulations. The flights met ASHRAE standard (3.5 L/s/p)
for 80% during boarding and the vast majority of time
Figure 2. Box plots of (a) CO
2
concentrations and (b) outside airflow rates by flight phases.
Figure 1. Measured CO
2
concentration and pressure during a typical flight.
6Indoor and Built Environment 0(0)
(96%) during flying, but this is a minimum for accept-
able air quality. They only met the FAR design require-
ment of 4.7 L/s/p, 42% of time during boarding and
73% of time during flying. Figure 4 shows the proba-
bility distributions of outside airflow rates during
boarding and cruising with an interval of 0.5 L/s/p.
The values higher than 20 L/s/p during boarding
(0.2%) are not shown for a clear comparison. The
black curve shown in each plot represents the corre-
sponding normal distribution with the same mean
value and standard deviation. As compared to the
black curve, the distribution of outside airflow rates
during boarding is obviously more positively skewed
(skewness ¼3.119) to the low end than during cruising
(skewness ¼1.964). Therefore, the boarding phase was
characterized by worse ventilation performance com-
pared to the cruising phase. A part of the very low
ventilation rates calculated for the boarding phase
may be not accurate due to the fact that the high
CO
2
concentration was changing rapidly in the begin-
ning of boarding. The effect of increased metabolic
activity during boarding may also account, in part,
for the increased CO
2
concentrations. Nevertheless,
the high CO
2
concentrations seen during boarding are
indicative of contaminants not being removed effective-
ly from the air by the ventilation.
Discussion
Cabin outside air ventilation rates were lower than
those typically found in other indoor environments.
Low ventilation and high physical activity levels possi-
bly increase the risk for airborne infectious disease
transmission, discomfort and other complaints. Low
ventilation rates in buildings are strongly associated
with higher risks of infectious airborne disease trans-
mission.
42
For instance, a recent study indicated that
crowded dormitories with low outdoor airflow rates
were associated with more respiratory infections
among college students.
43
Similarly, risk of disease
transmission within the aircraft cabin also seems to
be affected by ventilation.
2
A study of in-flight tuber-
culosis revealed that doubling ventilation rate within
the cabin could halve the infection risk.
44
On the
tested flights, passengers spent 20% of their boarding
time with equivalent ventilation rates below 3.5 L/s/p
and 58% of their time with rates below 4.7 L/s/p. Our
results showing low ventilation rates during boarding
also suggest that characterizing in-cabin exposures
based only on cruising conditions may overlook the
critical exposures likely occurring during ground oper-
ations. A recent Airport Cooperative Research
Program (ACRP) report
45
has highlighted the increas-
ing risks of transmission of infectious aerosols while the
aircraft is parked at the gate and APUs are shutdown.
Figure 3. Percentages of in-cabin outside airflow rates
met the aircraft regulations.
Figure 4. Probability distributions of outside airflow rates during boarding and cruise.
Cao et al. 7
The elevated CO
2
concentrations in the airplane
cabin are also of interest in light of recent studies on
impacts of CO
2
and ventilation on cognitive function
of occupants that saw effects at levels seen during all
flight phases. In a study of a controlled office environ-
ment,
21
participants were exposed to three CO
2
concen-
trations for 8 h each while they completed their normal
work activities. At the end of each day, they completed
1.5-h cognitive tests. Participants scored 15% and 50%
lower on cognitive tests on days when they were
exposed to 950 ppmv and 1400 ppmv of CO
2
, respec-
tively, compared to the reference condition of 550
ppmv. Similar findings were shown by Satish et al.
24
during 2.5-h exposure windows. Detrimental impacts
on cognitive function may influence the performance
of flight crew. In particular, the poor ventilation per-
formance during boarding warrant more attention. The
flight deck door is usually open during boarding, which
means CO
2
concentrations on the flight deck could be
influenced by the high CO
2
concentrations in the cabin.
Elevated CO
2
concentrations on the flight deck may
impact pilot performance during the subsequent taxiing
and take-off. A study by Allen et al. found that pilots
had 1.52 times higher odds of passing flight maneuvers
at 1500 ppm and 1.69 times higher odds at 700 ppm
compared to 2500 ppm, as rated by a FAA Designated
Pilot Examiner during simulated flight sessions. Pilots
were particularly impacted during maneuvers following
boarding; passing rates were twice as high at 700 ppm
and 1500 ppm during a takeoff with an engine fire than
at 2500 ppm, and four times as high at 700 ppm during
a rejected takeoff than at 2500.
46
In addition to cog-
nitive function, studies have found impacts on acute
health symptoms and physiological indicators such as
heart rate variability and peripheral blood circulation
from high indoor CO
2
levels.
47,48
Indoor CO
2
levels
higher than 800 ppm were associated with an increase
in workers’ SBS symptoms, such as eye irritation and
upper respiratory symptoms.
49
The measured ranges of CO
2
concentrations/outside
airflow rates were also comparable to other studies.
Spengler et al.
32
studied the cabin air quality during
the cruise phase of 83 flights flying US domestic and
international routes. In their study, the CO
2
concentra-
tions were 1404 297 ppmv with a range of 863–2065
ppmv, correspondingly the outside airflow rate was 5.5
1.8 L/s/p with a range of 3.0 to 10.9 L/s/p. Giaconia
et al.
37
measured the CO
2
concentrations on 14 short-
haul flights with A319 in Italy. The concentrations of
CO
2
varied between 734 and 2252 ppmv from boarding
to disembarking, which corresponded to outside air-
flows of 14.60 and 2.76 L/s/p, respectively. The mean
CO
2
concentrations on each flight ranged from 925 to
1449 ppmv, with the corresponding outside airflow
rates from 5.18 to 10.56 L/s/p. Similarly, Li et al.
13
reported that concentrations of CO
2
varied from 792
to 2253 ppmv during five domestic flights with Boeing
737–800 in China. The mean CO
2
concentration on
each flight ranged from 976 to 1135 ppmv, with the
corresponding outside airflow rates from 7.18 to 9.79
L/s/p. Hocking
50
calculated the ventilation capacity for
several representative aircraft types (Airbus, Boeing,
MD, USA) using their designed air exchange rates,
and reported that the outside air ventilation capacity
was within the range of 3.2 to 11.2 L/s/p. Our mean
outside ventilation rates were well within this range for
all 24 aircraft types.
The finding of higher CO
2
concentrations during
boarding was consistent with previous studies. In a
study of 16 flights, Lee et al.
33
found substantially
higher CO
2
concentrations during boarding and
deplaning than during cruising. They noted that CO
2
concentrations were higher during boarding and de-
boarding with typical levels of 2000 to 2500 ppmv.
Likewise, in a study of 26 intercontinental flights with
Boeing 767–300, Lindgren and Norb
ack
51
found higher
CO
2
concentrations during non-cruise conditions due
to low air exchange rates. The CO
2
concentrations were
1656 ppmv under non-cruise conditions compared to
734 ppmv during cruise.
According to previous studies, the average bleed air
fraction of the air supplied the cabin is typically about
0.5 during the whole flight.
11,13,52
Thus, the mean total
ventilation rate may be approximately twice the mean
outside airflow rate (11.54 L/s/p). We used sampling
duration as a proxy to test the influence of flight dura-
tion. The tested flights included mostly short-haul
flights (<2 h) and the rest were medium-haul flights
(2–6 h). No significant difference for the mean outside
airflow rate can be found between the short-haul flights
with duration t<1 h and 1 h <t<2h (p¼0.944). The
ventilation rates were slightly higher on the medium-
haul flights (p<0.0001). The results of this study may
not be representative of average conditions on long-
haul international flights which have a longer cruise
phase and where high activity during boarding and
deplaning constitute a shorter fraction of the overall
flight experience.
The estimation of outside airflow rate has some
uncertainties. Through Monte Carlo simulations, we
estimated that the range of CO
2
generation rate by a
passenger is 17–19.3 L/h,
32
thus resulting a maximum
deviation of 6% for the estimated outside ventilation
rates due to uncertainty in metabolic rate. Our gener-
ation rate is consistent with that used by ASHRAE
19
(18 L/h), which corresponds to an average size adult
engaged in typical office work (1.2 METs). However,
other values have been suggested depending on sub-
jects. For example, Lee and Siconolfi
53
measured CO
2
generation rate of 23 astronauts in a seated position
8Indoor and Built Environment 0(0)
and obtained a value of 13.2 1.2 L/h. A recent study
54
suggested that CO
2
generation rates of young Chinese
people were overestimated by the empirical equation
used in our research, which should be corrected by
factors of 0.75 and 0.85 for females and males under
sitting/standing conditions, respectively. The genera-
tion rates of passengers may be increased during a frac-
tion of boarding phase when physical activity levels
were elevated. However, it is worth noting that a pas-
senger is seated during most of the boarding and taxi-
ing process before taking-off. For a sensitive test, we
assumed that on average the highest 10% of CO
2
con-
centrations was recorded during a passenger walking
inside the cabin and lifting up the luggage with a met-
abolic rate of 3 METs (implied walking, putting away
household items, moderate effort).
40
Under this
assumption, the median of ventilation rates during
boarding would increase to 4.77 L/s/p with an IQR
of 1.49 L/s/p, still significantly lower compared to
other phases (p<0.0001).
The application of constant concentration method
was based on the assumption that the in-cabin air
was well mixed by ventilation and the only source of
CO
2
was the respiration by passengers. The well-mixed
assumption has been validated by several experimental
studies.
30,55,56
However, no information was available
concerning whether there was any other source of CO
2
on tested flights (e.g. dry ice used for chilling food and
beverages in the galley systems). As discussed previous-
ly, rapid changes in CO
2
concentration will introduce
errors in the calculated rate. However, these errors
should have minimal effect on the average rates calcu-
lated over the period of a flight phase. These uncertain-
ties may lead to over- or underestimating ventilation
rates, but do not affect findings related to the absolute
CO
2
levels.
Conclusions
In this study of 179 US domestic flights, we found that
96% of the observations met the minimum recom-
mended outside airflow rates for acceptable air quality
during the flying phases (3.5 L/s/p), but only 73% met
the rate required by the FAR (4.7 L/s/p). The CO
2
levels on all flights were well below the occupational
exposure limit of 5000 ppmv. The ground operation
phases, especially the boarding phase, had higher
CO
2
concentrations than the flying phases, likely due
to the inadequate ground ventilation on many flights
and higher metabolic rates during boarding.
Ventilation rates were highest during the cruising
phase. Current ventilation requirements are often not
met, particularly during the boarding phase, which is of
concern because low ventilation in other settings has
been associated with increased rates of disease
transmission, increased upper respiratory symptoms,
and worse performance on cognitive function tests.
Verification of ventilation performance rather than reli-
ance on design estimates for determining compliance
with regulatory mandated minimum outdoor air venti-
lation rates is recommended.
Authors’ contribution
All authors contributed to the data analysis and manuscript
preparation. BJ and SML led the field sampling effort. CZ,
JGA, JDS, BC, and EM were involved in the initial data
analysis and manuscript preparation. XC and PM led the
final data analysis and manuscript preparation in coordina-
tion with JGA, BC and JDS. All authors contributed to and
approved the final manuscript.
Acknowledgements
Although the FAA has sponsored this project, it neither
endorses nor rejects the findings of this research. We thank
the anonymous peer-reviewers for their excellent comments
that have enhanced the manuscript.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of
this article.
Funding
The author(s) disclosed receipt of the following financial sup-
port for the research, authorship, and/or publication of this
article: This study was funded partially by the US Federal
Aviation Administration (FAA) Office of Aerospace
Medicine through the National Air Transportation Center
of Excellence for Airliner Cabin Environment Research
(ACER)/Research in the Intermodal Transport
Environment (RITE), Cooperative Agreements 10-C-RITE-
HU, 07-C-RITE-HU and 04-C-ACE-HU.
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Cao et al. 11
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Recent decades have seen an increase in the interest of airlines in providing more comfortable environmental conditions for passengers. Nowadays, passengers in air transportation are demanding in terms of comfort. The ability to resolve problems in aircraft cabins is becoming crucial in ensuring passengers' happiness with their flights. It has been accommodated by major aircraft manufacturers such as Boeing and Airbus have been working to improve the comfort of their aircraft cabins. Thermal comfort for humans is one of the most severe issues addressed in buildings and aircraft. Providing thermal comfort for passengers and crew members is a complex problem in an aircraft because thermal comfort is affected by temperature and elements such as relative humidity, air velocity, environment radiation, activity level, and the insulation provided by clothing. The current study has introduced the following factors: human metabolic rate, insulation of clothing, and gender, which are human factors. The other factors are environmental factors: mean radiant temperature, low relative humidity, and colored light, low relative humidity, mean radiant temperature, colored light Many related studies and literature reviews have been conducted on the thermal comfort of indoor environments in ground-level buildings. However, only a few studies have been conducted on the thermal comfort of medium distance flight. Towards that aim, this work attempts to assemble a collection of publications on passenger thermal comfort that are relevant to studies on the thermal comfort of airline cabins.
... Following that, it maintains the temperature in each cabin within a comfortable range ranging from 15°C to 35°C. After that, the Air Conditioning System is utilized to feed air for cabin pressurization to maintain an appropriate outlet pressure [35]. The air cycle in the air conditioning system and the vapor cycle in the air conditioning system are the two types of air conditioning systems found in most commercial airplanes. ...
... In agreement with Yu et.al [48], the ventilation function is carried out by a ventilation monitoring system composed mostly of electrically driven fans and valves as well as sensors, controllers, and software, among other components. According to Cao et.al [35], the air ventilation system of an airplane currently has significant shortcomings when it comes to cooling high heat loads, which might result in unpleasant dryness, noise, or the dispersal of pollutants. The combining ventilation system is employed in the conventional process that is used in an airplane. ...
Article
Recent decades have seen an increase in the interest of airlines in providing more comfortable environmental conditions for passengers. Nowadays, passengers in air transportation are demanding in terms of comfort. The ability to resolve problems in aircraft cabins is becoming crucial in ensuring passengers' happiness with their flights. It has been accommodated by major aircraft manufacturers such as Boeing and Airbus have been working to improve the comfort of their aircraft cabins. Thermal comfort for humans is one of the most severe issues addressed in buildings and aircraft. Providing thermal comfort for passengers and crew members is a complex problem in an aircraft because thermal comfort is affected by temperature and elements such as relative humidity, air velocity, environment radiation, activity level, and the insulation provided by clothing. The current study has introduced the following factors: human metabolic rate, insulation of clothing, and gender, which are human factors. The other factors are environmental factors: mean radiant temperature, low relative humidity, and coloured light, low relative humidity, mean radiant temperature, and coloured light Many related studies and literature reviews have been conducted on the thermal comfort of indoor environments in ground-level buildings. However, only a few studies have been conducted on the thermal comfort of medium distance flight. Towards that aim, this work attempts to assemble a collection of publications on passenger thermal comfort that are relevant to studies on the thermal comfort of airline cabins.
... [8]. In a similar approach on 179 domestic US flights Cao et al. [9] found an average CO 2 concentration of 1353 ± 290 ppm in the cabin. The researchers clearly state that sensor readings were pressure compensated. ...
... A clear trend of increased cabin relative humidity with decreasing outside airflow rate is obvious (Figure 9). In the "Baseline" conditions, values around 15% RH were measured that are well in line with other publications [7,9]. For the "ASHRAE half" and "Max. ...
Article
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In the CleanSky 2 ComAir study, subject tests were conducted in the Fraunhofer Flight Test Facility cabin mock-up. This mock-up consists of the front section of a former in-service A310 hosting up to 80 passengers. In 12 sessions the outdoor/recirculation airflow ratio was altered from today’s typically applied fractions to up to 88% recirculation fraction. This leads to increased relative humidity, carbon dioxide (CO2) and Total Volatile Organic Compounds (TVOC) levels in the cabin air, as the emissions by passengers become less diluted by outdoor, dry air. This paper describes the measured increase of relative humidity, CO2 and TVOC level in the cabin air for the different test conditions.
... Because ventilation is the most crucial activity in the cabin for maintaining indoor environmental quality, maintaining adequate ventilation rates aboard is critical for creating comfortable and vigorous cabin environments (Cao et al. 2019). In order to improve cabin air quality, it is critical to study air dispersion in commercial aircraft cabins. ...
Article
The mixing ventilation (MV) system, could spread airborne infectious diseases in airplane cabins, such as the flu and Corona-virus infection (COVID-19). As a result, it is critical to improve the current design of airline cabin ventilation systems. Six innovative customized ventilation (PV) systems were proposed and investigated through numerical simulations in this study to reduce pollutant transport. At first, two environmental chambers' experimental data on airflow, air temperature, and pollutant concentration were utilized to validate the Computational Fluid Dynamics (CFD) model used for the present numerical study. The six PVs were then studied to analyze the distributions of air velocity, air temperature, pollutant concentration, and carbon dioxide (CO 2) concentration in a part of the Boeing 767 cabin using the validated CFD model. It is found that the passenger's personal outlet set up on both sides of his or her head (PV-1) has the best distribution of carbon dioxide concentration, velocity, temperature, and contaminant concentration when compared to the six personalized air distribution systems. It can reduce pollutant concentrations more than the other proposed systems. The present study may shed new light on the design of PVs with the potential for reducing the spreading of airborne infectious diseases.
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Article
Carbon dioxide (CO2) is an important environmental parameter in aircraft cabins. To understand the most recent, real‐time CO2 concentration levels and their key influencing factors in aircraft cabins, we conducted in‐flight measurements of 52 randomly selected commercial flights with different aircraft types and durations from August 2017 to August 2019. The spatial temporal characteristics of CO2 concentrations on board were analyzed and summarized. For the flight time scale, the CO2 concentrations during the boarding phase (1680 ± 558 ppmv) were notably higher than that in other phases, whereas the condition of the cruising phase was the lowest in most flights. The flight average CO2 concentrations of the cruising phase were 1253 ± 164 ppmv, and the corresponding estimated outside airflow rates were 6.2 ± 1.3 L/s/p in the economy class across all flights. Single‐aisle and twin‐aisle flights did not show noticeable differences for the same phases. Relatively uniform CO2 concentrations were observed at different positions of the same class. By comparing the results of this study with those previously reported, CO2 concentrations showed a slightly decreasing trend over the last 30 years. This suggested a slightly increased ventilation rate and potentially superior air quality on board.
Article
We reviewed 47 documents published 1967–2019 that reported measurements of volatile organic compounds (VOCs) on commercial aircraft. We compared the measurements with the air quality standards and guidelines for aircraft cabins and in some cases buildings. Average levels of VOCs for which limits exist were lower than the permissible levels except for benzene with average concentration at 5.9 ± 5.5 μg/m3. Toluene, benzene, ethylbenzene, formaldehyde, acetaldehyde, limonene, nonanal, hexanal, decanal, octanal, acetic acid, acetone, ethanol, butanal, acrolein, isoprene and menthol were the most frequently measured compounds. The concentrations of semi‐volatile organic compounds (SVOCs) and other contaminants did not exceed standards and guidelines in buildings except for the average NO2 concentration at 12 ppb. Although the focus was on VOCs, we also retrieved the data on other parameters characterizing cabin environment. Ozone concentration averaged 38 ppb below the upper limit recommended for aircraft. The outdoor air supply rate ranged from 1.7 to 39.5 L/s per person and averaged 6.0 ± 0.8 L/s/p (median 5.8 L/s/p), higher than the minimum level recommended for commercial aircraft. Carbon dioxide concentration averaged 1315 ± 232 ppm, lower than what is permitted in aircraft and close to what is permitted in buildings. Measured temperatures averaged 23.5 ± 0.8°C and were generally within the ranges recommended for avoiding thermal discomfort. Relative humidity averaged 16% ± 5%, lower than what is recommended in buildings.
Article
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In the CleanSky 2 ComAir study, subject tests were conducted in the Fraunhofer Flight Test Facility cabin mock-up. This mock-up consists of the front section of a former in-service A310 hosting up to 80 passengers. In 12 sessions the outdoor/recirculation airflow ratio was altered from today’s typically applied fractions to up to 88% recirculation fraction. This leads to increased relative humidity, carbon dioxide (CO2) and Total Volatile Organic Compounds (TVOC) levels in the cabin air, as the emissions by passengers become less diluted by outdoor, dry air. This paper describes the measured increase of relative humidity, CO2 and TVOC level in the cabin air for the different test conditions.
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Background: Recent studies suggest that carbon dioxide has an impact on cognitive function performance of office workers at concentrations previously thought to be benign (1000-2500 ppm). The only available data for CO2 on the flight deck indicate that the average CO2 concentrations are typically <1000 ppm, but the 95th percentile concentration can be as high as 1400 ppm, depending on airplane type. Methods: We recruited 30 active commercial airline pilots to fly three 3-h flight segments in an FAA-approved flight simulator with each segment at a different CO2 concentration on the flight deck (700, 1500, 2500 ppm). CO2 concentrations were modified by introducing ultra-pure CO2 into the simulator; ventilation rates remained the same for each segment. The pilots performed a range of predefined maneuvers of varying difficulty without the aid of autopilot, and were assessed by a FAA Designated Pilot Examiner according to FAA Practical Test Standards. Pilots and the Examiner were blinded to test conditions and the order of exposures was randomized. Results: Compared to segments at a CO2 concentration of 2500 ppm, the odds of passing a maneuver as rated by the Examiner in the simulator were 1.52 (95% CI: 1.02-2.25) times higher when pilots were exposed to 1500 ppm and 1.69 (95% CI: 1.11-2.55) times higher when exposed to 700 ppm, controlling for maneuver difficulty, Examiner and order of maneuvers. Discussion: Examiner rating captured a wider range of performance indicators than output from the flight simulator, which can characterize only a few quantitative aspects of the flight performance. More broadly, these findings suggest that there is a direct effect of carbon dioxide on performance, independent of ventilation, with implications for many other indoor environments that routinely experience CO2 concentrations above 1000 ppm.
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Background The Germanwings Flight 9525 crash has brought the sensitive subject of airline pilot mental health to the forefront in aviation. Globally, 350 million people suffer from depression–a common mental disorder. This study provides further information on this important topic regarding mental health especially among female airline pilots. This is the first study to describe airline pilot mental health–with a focus on depression and suicidal thoughts–outside of the information derived from aircraft accident investigations, regulated health examinations, or identifiable self-reports, which are records protected by civil aviation authorities and airline companies. Methods This is a descriptive cross-sectional study via an anonymous web-based survey administered between April and December 2015. Pilots were recruited from unions, airline companies, and airports via convenience sampling. Data analysis included calculating absolute number and prevalence of health characteristics and depression scores. Results One thousand eight hundred thirty seven (52.7%) of the 3485 surveyed pilots completed the survey, with 1866 (53.5%) completing at least half of the survey. 233 (12.6%) of 1848 airline pilots responding to the Patient Health Questionnaire 9 (PHQ-9), and 193 (13.5%) of 1430 pilots who reported working as an airline pilot in the last seven days at time of survey, met depression threshold–PHQ-9 total score ≥ 10. Seventy-five participants (4.1%) reported having suicidal thoughts within the past two weeks. We found a significant trend in proportions of depression at higher levels of use of sleep-aid medication (trend test z = 6.74, p < 0.001) and among those experiencing sexual harassment (z = 3.18, p = 0.001) or verbal harassment (z = 6.13, p < 0.001). Conclusion Hundreds of pilots currently flying are managing depressive symptoms perhaps without the possibility of treatment due to the fear of negative career impacts. This study found 233 (12.6%) airline pilots meeting depression threshold and 75 (4.1%) pilots reporting having suicidal thoughts. Although results have limited generalizability, there are a significant number of active pilots suffering from depressive symptoms. We recommend airline organizations increase support for preventative mental health treatment. Future research will evaluate additional risk factors of depression such as sleep and circadian rhythm disturbances. Electronic supplementary material The online version of this article (doi:10.1186/s12940-016-0200-6) contains supplementary material, which is available to authorized users.
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Thirty years of public health research have demonstrated that improved indoor environmental quality is associated with better health outcomes. Recent research has demonstrated an impact of the indoor environment on cognitive function. We recruited 109 participants from 10 high-performing buildings (i.e. buildings surpassing the ASHRAE Standard 62.1–2010 ventilation requirement and with low total volatile organic compound concentrations) in five U.S. cities. In each city, buildings were matched by week of assessment, tenant, type of worker and work functions. A key distinction between the matched buildings was whether they had achieved green certification. Workers were administered a cognitive function test of higher order decision-making performance twice during the same week while indoor environmental quality parameters were monitored. Workers in green certified buildings scored 26.4% (95% CI: [12.8%, 39.7%]) higher on cognitive function tests, controlling for annual earnings, job category and level of schooling, and had 30% fewer sick building symptoms than those in non-certified buildings. These outcomes may be partially explained by IEQ factors, including thermal conditions and lighting, but the findings suggest that the benefits of green certification standards go beyond measureable IEQ factors. We describe a holistic “buildingomics” approach for examining the complexity of factors in a building that influence human health.
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Green buildings are designed to have low environmental impacts and improved occupant health and well-being. Improvements to the built environment including ventilation, lighting, and materials have resulted in improved indoor environmental quality (IEQ) in green buildings, but the evidence around occupant health is currently centered around environmental perceptions and self-reported health. To investigate the objective impact of green buildings on health, we tracked IEQ, self-reported health, and heart rate in 30 participants from green and conventional buildings for two weeks. 24 participants were then selected to be relocated to the Syracuse Center of Excellence, a LEED platinum building, for six workdays. While they were there, ventilation, CO2, and volatile organic compound (VOC) levels were changed on different days to match the IEQ of conventional, green, and green+ (green with increased ventilation) buildings. Participants reported improved air quality, odors, thermal comfort, ergonomics, noise and lighting and fewer health symptoms in green buildings prior to relocation. After relocation, participants consistently reported fewer symptoms during the green building conditions compared to the conventional one, yet symptom counts were more closely associated with environmental perceptions than with measured IEQ. On average, participants had 4.7 times the odds of reporting a lack of air movement, 43% more symptoms (p-value = 0.019) and a 2 bpm higher heart rate (p-value < 0.001) for a 1000 ppm increase in indoor CO2 concentration. These findings suggest that occupant health in green and conventional buildings is driven by both environmental perceptions and physiological pathways.
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Abstract Above rules-of-thumb ventilation standard based on air change rate per hour (ACH), it is necessary to assess the indoor airflow and indoor air quality (IAQ) with respect to simple dimensionless numbers from the practical point of view. Hence, this work aims at investigating the influence of air change rates on indoor CO2 stratification and removal with dimensionless time scale ratio (proportional to Ri/α, Richardson number Ri, mass flux ratio α) and vorticity by applying experiment and simulation methods. We firstly carried out a series of experiments with different ACHs along with constant CO2 pollutant sources, further for simulation validation. Next, numerical simulation was employed to investigate five different ACHs (ranged from 4 to 28) on indoor CO2 concentration for two different vent-inlet-size cases. It was found that as the increase of ACH, the averaging outlet CO2 concentration was decreased until ACH equal to 16, both cases starting showing asymptotic behavior. When looking at indoor CO2 distribution, the case with larger vent-inlet size showed clear stratification even with higher ACH value (i.e., 28), due to the relatively smaller vorticity value (i.e., 0.47, with 3.14 for small-vent-size case) and larger Ri magnitude (37 times) compared to small-vent-size case. Specifically, it is beneficial for indoor CO2 removal to keep time scale ratio Ri/α below 10−3 and vorticity above 1 rather than merely following with high ACH values. These findings will be of great importance for practical applications to design and control ventilation systems in the perspective of health and energy efficiency.
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Passengers and crew on board of commercial airliners often spend extra time in the cabin waiting for departure due to flight delays. During the waiting period, a large amount of ambient ultrafine particles (UFPs) may penetrate into the aircraft cabin through the environmental control system (ECS) and ground airconditioning cart (GAC). However, limited data are available for human exposure, in waiting commercial airliners, to freshly emitted UFPs from the exhaust of ground vehicles and airliners. To address this issue, we measured the ambient and in-cabin particle number concentrations and particle size distributions (PSDs) simultaneously in an MD-82 airliner parked at Tianjin International Airport, China. When air was supplied to the cabin by GAC, particle counts variation outdoors caused in-cabin variation with a 1–2 min delay. The in-cabin and ambient PSDs ranged from 15 to 600 nm were bimodal, with peaks at 30–40 and 70–90 nm. The GAC and ECS removed 1–73% particles in the size range of 15–100 nm and 30–47% in the size range of 100–600 nm. The relationship between the penetration factor and particle size was an inverted U-curve. An improved particle dynamic model from this study was used to calculate the time-dependent in-cabin UFPs concentrations with dramatic changes in outdoor concentration.
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We hypothesized that elevations of carbon dioxide (CO2) commonly found in modern buildings will stimulate leukocytes to produce microparticles (MPs) and activate the nucleotide-binding domain-like receptor 3 (NLRP3) inflammasome due to mitochondrial oxidative stress. Human and murine neutrophils generate MPs with high interleukin-1β (IL-1β) content when incubated ex vivo in buffer equilibrated with 0.1 to 0.4% additional CO2. Enhanced MPs production requires mitochondrial reactive oxygen species production, which is mediated by activities of pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Subsequent events leading to MPs generation include perturbation of inositol 1,3,5-triphosphate receptors, a transient elevation of intracellular calcium, activation of protein kinase C and NADPH oxidase (Nox). Concomitant activation of type-2 nitric oxide synthase yields secondary oxidants resulting in actin S-nitrosylation and enhanced filamentous actin turnover. Numerous proteins are linked to short filamentous actin including vasodilator-stimulated phosphoprotein, focal adhesion kinase, the membrane phospholipid translocation enzymes flippase and floppase, and the critical inflammasome protein ASC (Apoptosis-associated Speck protein with CARD domain). Elevations of CO2 cause oligomerization of the inflammasome components ASC, NLRP3, caspase 1, thioredoxin interacting protein, and calreticulin - a protein from endoplasmic reticulum, leading to IL-1β synthesis. An increased production rate of MPs containing elevated amounts of IL-1β persists for hours after short-term exposures to elevated CO2.
Conference Paper
Frequent air travel and long flight duration makes the study of airliner cabin environmental quality a topic of utmost importance. Ventilation effectiveness is one of the more crucial factors affecting air quality in any environment. Ventilation effectiveness, along with the overall ventilation rate, is a measure of the ability of the air distribution system to remove internally generated pollutants or contaminants from a given space. Because of the high occupant density in an aircraft cabin, local variations in ventilation are important as a passenger will occupy the same space for the duration of the flight. Poor ventilation in even a small portion of the cabin could impact multiple people for extended time periods. In this study, the local effective ventilation rates and local ventilation effectiveness in an eleven-row, full-scale, Boeing 767 cabin mockup were measured. These measurements were completed at each of the 77 seats in the mockup. Each seat was occupied by a heated mannequin. In order to simulate the thermal load inside the cabin, the mannequins were wrapped with a heating wire to generate approximately 100 W (341 BTU/hour) of heat. Carbon dioxide was used as a tracer gas for the experiments and the tracer gas decay method was employed to calculate the local effective ventilation rate and local ventilation effectiveness. The overall ventilation rate, based on total supply air flow, was approximately 27 air changes per hour. Local ventilation effectiveness ranged from 0.86 to 1.02 with a mean value of 0.94. These ventilation effectiveness values are higher than typically found in other indoor applications and are likely due to the relatively high airspeeds present in the aircraft cabin and the high degree of mixing they provide. The uniformity is also good with no areas of particularly low ventilation effectiveness being identified. No clear patterns with respect to seat location, window versus center versus aisle, were found.
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A ventilation nozzle’s airflow characteristics could have an influence on a passenger’s thermal comfort and dispersion of pollutants in an aircraft cabin, but there is little published research in this area. In this article, the temperature and air velocity from a nozzle jet were measured in a simulated three-row aircraft cabin at more than 220 points for both isothermal and non-isothermal jets. The non-isothermal jets were tested for air supply temperature differences of ± 5 and 10℃, and the isothermal jets for volume flowrates of 1.86 × 10⁻⁷, 2.67 × 10⁻⁷, and 4.03 × 10−7 m³/h. The results show that both the nozzle jet’s temperature and air velocity distributions are axially symmetrical and that the decay of the jet is rapid. The equation for the air velocity distribution was used to calculate the air velocity at any point in the main jet region for different volume flowrates. The temperature difference was shown to have little effect on the air velocity distribution for the main region of a nozzle jet, whereas the air flowrate was shown to significantly affect the air velocity distribution. This suggests that the effect of nozzle jet on passenger’s thermal comfort is mostly due to its air velocity distribution rather than temperature distribution.
Article
To extend the results of a previous study on the effects of carbon dioxide (CO2) and bioeffluents on humans, the new study reported in this paper was carried out. The purpose of this study was to examine, whether exposure to CO2 at 5,000 ppm would cause sensory discomfort, evoke acute health symptoms, reduce the performance of cognitive tasks, or result in changes in physiological responses. The outdoor air supply rate was set high enough in a low-emission stainless-steel climate chamber to create a reference condition with CO2 at 500 ppm when subjects were present, and chemically pure CO2 was added to the supply air to create an exposure condition with CO2 at 5,000 ppm (the measured exposure level was ca. 4,900 ppm). Ten healthy college-age students were exposed twice to each of the two conditions for 2.5 hours in a design balanced for order of presentation. The raised CO2 concentration had no effect on perceived air quality or physiological responses except for end-tidal CO2 (ETCO2), which increased more (to 5.3 kPa) than it was in the reference condition (5.1 kPa). Other results indicate additionally that a 2.5-hour exposure to CO2 up to 5,000 ppm did not increase intensity of health symptoms reported by healthy young individuals and their performance of simple or moderately difficult cognitive tests and some tasks resembling office work. These results accord well with the current occupational exposure limit recommendation for CO2 and with many other reports published in the literature.