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

Otmar Geiss

doi:10.4209/aaqr.2020.07.0403

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.

Highlights

Received: July 15, 2020 Revised: October 1, 2020 Accepted: October 6, 2020Publisher: Taiwan Association for Aerosol Research ISSN: 1680-8584 print ISSN: 2071-1409 onlineCopyright: The Author's institution
It was included in the study to assess the potential impact of the exhalation valve on the concentration of accumulated carbon dioxide. c) Cloth masks: Since surgical and FFP2 masks were sometimes difficult to find at the beginning of the pandemic and, especially the FFP2 masks should be reserved for health care providers, cloth masks have become popular during the pandemic as they are cheap, easy to find or to make and can be washed and reused
Even with the one-way exhalation valve on the KN95 face mask, under these conditions, the type of mask had no significant impact on the carbon dioxide concentration in the breathing zone

Summary

Introduction

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 exhaled in the expiration air. 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)

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