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Correlation of Respiratory Aerosols and Metabolic Carbon Dioxide

Department of Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark
Airlabs, Nannasgade 28, 2200 Copenhagen, Denmark
Danish Big Data Centre for Environment and Health (BERTHA), Aarhus University, 4000 Roskilde, Denmark
Department of Environmental Science, Aarhus University, 4000 Roskilde, Denmark
Department of the Built Environment, Division of Sustainability, Energy and Indoor Environment, Aalborg University, 2450 Copenhagen, Denmark
Author to whom correspondence should be addressed.
Current address: Department of Geology, Lund University, 22362 Lund, Sweden.
Academic Editor: Giouli Mihalakakou
Sustainability 2021, 13(21), 12203;
Received: 27 September 2021 / Revised: 2 November 2021 / Accepted: 4 November 2021 / Published: 5 November 2021
(This article belongs to the Special Issue Sustainable Building and Sustainable Indoor Environment)
Respiratory aerosols from breathing and talking are an important transmission route for viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Previous studies have found that particles with diameters ranging from 10 nm to 145 μm are produced from different regions in the respiratory system and especially smaller particles can remain airborne for long periods while carrying viral RNA. We present the first study in which respiratory aerosols have been simultaneously measured with carbon dioxide (CO2) to establish the correlation between the two concentrations. CO2 concentrations are easily available through low-cost sensors and could be used to estimate viral exposure through this correlation, whereas source-specific aerosol measurements are complicated and not possible with low-cost sensors. The increase in both respiratory aerosols and CO2 was linear over ten minutes in a 2 m3 chamber for all participants, suggesting a strong correlation. On average, talking released more particles than breathing, with 14,600 ± 16,800 min−1 (one-σ standard deviation) and 6210 ± 5630 min−1 on average, respectively, while CO2 increased with 139 ± 33 ppm min−1 during talking and 143 ± 29 ppm min−1 during breathing. Assuming a typical viral load of 7×106 RNA copies per mL of oral fluid, ten minutes of talking and breathing are estimated to produce 1 and 16 suspended RNA copies, respectively, correlating to a CO2 concentration of around 1800 ppm in a 2 m3 chamber. However, viral loads can vary by several orders of magnitude depending on the stage of the disease and the individual. It was therefore concluded that, by measuring CO2 concentrations, only the number and volume concentrations of released particles can be estimated with reasonable certainty, while the number of suspended RNA copies cannot. View Full-Text
Keywords: respiratory aerosols; carbon dioxide; airborne transmission; indoor air quality; COVID-19 respiratory aerosols; carbon dioxide; airborne transmission; indoor air quality; COVID-19
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MDPI and ACS Style

Kappelt, N.; Russell, H.S.; Kwiatkowski, S.; Afshari, A.; Johnson, M.S. Correlation of Respiratory Aerosols and Metabolic Carbon Dioxide. Sustainability 2021, 13, 12203.

AMA Style

Kappelt N, Russell HS, Kwiatkowski S, Afshari A, Johnson MS. Correlation of Respiratory Aerosols and Metabolic Carbon Dioxide. Sustainability. 2021; 13(21):12203.

Chicago/Turabian Style

Kappelt, Niklas, Hugo Savill Russell, Szymon Kwiatkowski, Alireza Afshari, and Matthew Stanley Johnson. 2021. "Correlation of Respiratory Aerosols and Metabolic Carbon Dioxide" Sustainability 13, no. 21: 12203.

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