Co2 level UP in Air with CO2.

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On a recent two-hour United Airlines flight from my home in Asheville, NC., to a
connecting flight out of Chicago O’Hare, I decided to perform very rudimentary
measurements while on board to see how interior carbon dioxide (CO2)
concentrations might change throughout the flight. I did this because there has
been a lot of discussion lately about assessing airline cabin air quality, in particular
revolving around CO2 levels, and I wanted to see for myself what results I might
observe. Over the pages that follow I will describe my simple procedure and
My Measurement Inside an Airplane

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results, but first I’ll provide some background information on CO2 to build a
foundation as we move the discussion forward.
Carbon Dioxide in Our Bodies
In the human body, CO2 is formed intracellularly as a byproduct of metabolism.
CO2 is transported in the bloodstream to the lungs where it is ultimately removed
from the body through exhalation. The average human exhales about 2.3
pounds of CO2 on an average day. (The exact quantity depends on your activity
level—a person engaged in vigorous exercise produces up to eight times as
much CO2 as one that is sedentary.)
Under normal conditions when we exhale, the composition of the air remains
almost the same as the air we inhale, only the percentage of CO2 and oxygen
changes. The amount of inhaled air contains approximately 21% of oxygen and
0.04% of CO2, while the air we breathe out contains around 16.4% of oxygen and
4.4% of CO2. CO2 is a waste product and is transported in the opposite direction to
oxygen: It passes from the bloodstream – across the lining of the air sacs – into
the lungs and out into the atmosphere.
CO2 also enters the atmosphere through the burning of fossil fuels (coal, natural
gas, and oil) solid waste, trees, volcanos, and other biological materials, and
because of certain chemical reactions (e.g., manufacture of cement). Climate
change is primarily a problem of too much CO2 in the atmosphere, responsible in
part for the greenhouse effect leading to global warming.
CO2 is not poisonous as a gas and will not hurt you. This is an important fact to
remember, as carbon dioxide is a vital part of the environment. The human
breathing mechanism actual revolves around CO2, it’s only when it gets
concentrated that we may begin to worry.

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Indoor CO2 monitoring has been established as a surrogate for measuring human
occupancy, used to assess whether ventilation is adequate for the number of
people occupying a space. Increasing human occupancy will cause the CO2 levels
indoors to accumulate to higher levels unless removed through ventilation. CO2
levels may also serve as a proxy for other difficult to detect pollutants, particurally
human bioefluents such as body odor, or airborne respiratory emissions such as
viruses, bacteria, and other potentially infectious or dangerous pathogens of
concern.
Other Uses of CO2
You may find it interesting to know that medical-grade CO2 is used as a pure gas
or mixed with other gases to form specialized mixtures for various purposes
including anesthesia, breathing stimulation, and equipment sterilization. CO2 is
also used in minimal invasive surgeries such as laparoscopy, endoscopy, and
arthroscopy and in cryotherapy for removals of warts, moles, and skin tags. The
pharmaceutical manufacturing industry used CO2 in multiple steps of various
processes. CO2 is applied in the production of supercritical fluid chromatography,
and incubators use CO2 in the gas phase. CO2 is also used in the pH control of

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wastewater. The COVID-19 Pandemic, along with the war in the Ukraine and
other world disruptions, has contributed in multiple ways to the shortage of CO2
that the world has been experiencing since 2020.
My Measurement Apparatus
I used a simple, relatively inexpensive, and readily available CO2 meter made by
Aranet (model 4 APP). This device uses a nondispersive infrared (NDIR) sensor to
measure CO2 concentrations. The CO2 gas in the chamber adsorbs infrared light
and this absorption is measured by the sensor. The less light that passes through
the higher the CO2 concentration. CO2 absorbs only a specific wavelength of light;
therefore, an optical filter is used. This device updates its measurement display
for every 5 minutes it is in operation.
Flying High with Carbon Dioxide
The volume percentage of CO2 in the air remains almost constant with increasing
elevation (apart from local modifications near the ground). Consequently, its
partial pressure or concentration (mass per volume) decreases as the barometric
pressure falls with increasing altitude.
CO2Meter, a supplier of measurement equipment, provides a rule of thumb that
states the CO2 level at altitude will change about 3% for every 1,000 feet (300m).
Assuming an average cruising height of 20,000 feet, with ground level CO2
concentration of 450 ppm, the CO2 level at flight altitude would be approximately
60% less, or about 180 ppm.

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Carbon Dioxide in the Cabin
My procedures and measurement of CO2 concentrations within the plane’s cabin
was simple, straightforward and I’m sure fraught with error, but I found the
results compelling and worthy of future investigation. I’ll include making air ion
concentration measurements next time. My set-up for testing is shown in the
photo below, and consisted of me in my seat, holding the Aranet device on top of
a magazine in my lap for the entire trip.
This was a United Airlines flight on a Canadair CL-65 airplane. I was seated in
business class, first row, left hand side, two people per row, aisle seat #C1. The
flight was scheduled for March 26th
, 2022 with boarding beginning at 6:35am (ET),
departure at 7:00am, and arrival at 8:02am (CT) for a 2hr 02 min duration. All
seats were filled, less one. The flight took off on time and under good weather
conditions, arriving a few minutes early. The plane’s interior layout and my
seating position is shown in the diagram below.

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From the time I boarded, throughout the duration of flight and until the plane had
come to a stop at the connecting terminal, I allowed the meter to measure and
display CO2 concentrations while I recorded each changing measurement (every 5
minutes). I took cell phone pictures of each event, and a few of those are shown
below.

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I made a log of cabin CO2 concentrations over time, which is shown below.
Elevating the Discussion
The Canadair CL-65 specification states that this is a 50-passenger plane with a
cabin length of 40 ft 6 in, a maximum (centerline) width of 8 ft 3 in, maximum
height of 6 ft 1 in, a floor area of 290.25 square feet, and a cabin volume of 1,687
cubic feet. This flight consisted of 49 passengers and 1 flight attendant (50 total)
occupying the main cabin. Using 180 ppm CO2 as the baseline outdoors, and an
average cabin CO2 measurement of 1511 ppm, I applied the National Institute of
Standards and Technology (NIST) Indoor Carbon Dioxide Metric Analysis Tool
available online at https://pages.nist.gov/CONTAM-apps/webapps/CO2Tool/#/
By manipulating the input ventilation rate per person to achieve the resulting CO2
average I had measured, the tool quickly estimated what the equivalent
commercial building ventilation rate in cfm per person would be. I thought this
calculation might make my results more relatable. That calculation outcome is
shown below.

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The program inputs I made under the “user defined” option included 1.3 met per
person and resulted in a 7.5 cfm per person ventilation rate, which seems low in
comparison to what we might typically see in an equivalent fully occupied indoor
environment, perhaps ventilated with outdoor air at a rate closer to 15 cfm per
person. The calculated air changes rate for the airline cabin space was 13.34 ACH.
Not being familiar with commercial airplane ventilation standards or practices, I
can draw no conclusions to its acceptability.
Of interest is the comparison in CO2 concentrations measure on my connecting
flight from Chicago to St. Louis. This was a United Airlines flight on a CRJ550
airplane. I was bumped up to first class on this flight, first row, left hand side, two
persons per row, window seat. Boarding began at 8:34am (CT), departure at
9:05am, and arrival at 10:26am (1hr 21 min duration). The plane was occupied to
capacity. CO2 measurements were conducted throughout the flight, with a low of
1149 ppm which never peaked above 1400 ppm, including any runway time.
Average concentrations were approximately 1275 ppm. These measurements
were lower than my first flight, perhaps based on a newer plane, more passenger
room in first class, or a better ventilation system. Lesson learned, always fly first
class if you want to breathe “better” air.

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My crude experiment probably didn’t prove much as it was a single test (no
replicates) and the measurement device was not laboratory quality, but I can brag
that the batteries were almost fully charged. I had a fun time performing the test
which helped pass the time, and I finished reading my latest ASHRAE Journal
magazine as well, so I felt it productive. I’m on-and-off airplanes almost every
week, sometimes taking four flights per week, so this was a nice distraction from
my normal routine…and who knows, I may l have gained some knowledge that
will prove useful one day down the road.
As mentioned, I’d like to run simultaneous CO2 and air ionization measurements,
maybe even throw in particle and TVOC counts as well. I do however worry about
getting all the required measurement gear through security, as well as the stares I
might receive from other passengers when they see a guy onboard dressed up
like a weather station. I guess if my next flight is on Halloween, I might just be
able to pull it off.
Authors Bio:
David Schurk DES, CEM, LEED-AP, CDSM, CWEP, SFP, CIAQM is the Director of
Healthcare and Applied Engineering Markets for GPS Air in Charlotte, NC.