ORIGINAL RESEARCH
https://doi.org/10.4209/aaqr.2020.07.0403

Aerosol and Air Quality
Research

Effect of Wearing Face Masks on the Carbon
Dioxide Concentration in the Breathing Zone
Otmar Geiss*

Special Issue:
Special Issue on COVID-19 Aerosol
Drivers, Impacts and Mitigation (X)

European Commission, Joint Research Centre (JRC), Ispra, Italy

ABSTRACT
The use of face masks is among the measures taken to prevent person-to-person transmission
of the virus (SARS-CoV-2) responsible for the coronavirus disease (COVID-19). Lately, concern was
expressed about the possibility that carbon dioxide could build up in the mask over time, causing
medical issues related to the respiratory system. In this study, the carbon dioxide concentration
in the breathing zone was measured while wearing a surgical mask, a KN95 and a cloth mask. For
the surgical mask, the concentration was determined under different conditions (office work,
slow walking, and fast walking). Measurements were made using a modified indoor air quality
meter equipped with a nondispersive infrared (NDIR) CO2 sensor. Detected carbon dioxide
concentrations ranged from 2150 ± 192 to 2875 ± 323 ppm. The concentrations of carbon dioxide
while not wearing a face mask varied from 500–900 ppm. Doing office work and standing still on
the treadmill each resulted in carbon dioxide concentrations of around 2200 ppm. A small
increase could be observed when walking at a speed of 3 km h–1 (leisurely walking pace). Walking
at a speed of 5 km h–1, which corresponds to medium activity with breathing through the mouth,
resulted in an average carbon dioxide concentration of 2875 ppm. No differences were observed
among the three types of face masks tested. According to the literature, these concentrations
have no toxicological effect. However, concentrations in the detected range can cause
undesirable symptoms, such as fatigue, headache, and loss of concentration.
Keywords: Face masks, Carbon dioxide, SARS-CoV-2, COVID-19 pandemic, COVID-19

1 INTRODUCTION

OPEN ACCESS

Received: July 15, 2020
Revised: October 1, 2020
Accepted: October 6, 2020
* Corresponding

Author:

otmar.geiss@ec.europa.eu

Publisher:
Taiwan Association for Aerosol
Research
ISSN: 1680-8584 print
ISSN: 2071-1409 online
Copyright: The Author's
institution. This is an open access
article distributed under the terms
of the Creative Commons
Attribution License (CC BY 4.0),
which permits unrestricted use,
distribution, and reproduction in
any medium, provided the original
author and source are cited.

Physical distancing, good hand hygiene and the wearing of gloves and face masks are among
the most frequent measures taken to prevent person-to-person transmission of the virus (SARSCoV-2) responsible for the coronavirus disease (COVID-19) since the outbreak of the COVID-19
pandemic in early 2020 (Chu et al., 2020; Howard et al., 2020). Especially, the use of face masks
in public reduces the spread of the virus by minimizing the excretion of respiratory droplets from
asymptomatic infected individuals or individuals who have not yet developed symptoms
(Bourouiba, 2020). The human body utilizes oxygen and generates carbon dioxide, which is then
exhaled in the expiration air. An adult with healthy lungs produces approximately 5.6% by volume
of CO2. When wearing a face mask, a fraction of carbon dioxide previously exhaled is inhaled
again with each respiratory cycle. Some media have been claiming that carbon dioxide may slowly
build up in the mask over time, causing medical issues related to the respiratory system such as
hypercapnia (a condition arising from too much carbon dioxide in the blood).
Only a few studies have been conducted so far in this field. In a study conducted by Sinkule et
al. (2013), the breathing air quality when using N95 filtering facepiece respirators was assessed.
The concentration of carbon dioxide increased to approximately 1.2–3% in a short period of light
work. The participants did not show any obvious changes in physical functions. The average
carbon dioxide concentration inhaled was, however, far higher than the limit of 0.1% of indoor
carbon dioxide concentration in many countries. The study of Li et al. (2005) investigated the
effects of wearing N95 and surgical face masks with and without nano-functional treatments on
thermo-physiological responses and the subjective perception of discomfort in five healthy

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