Correlation of Respiratory Aerosols and Metabolic Carbon Dioxide

Abstract

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.

Informing Building Strategies to Reduce Infectious Aerosol Transmission Risk by Integrating DNA Aerosol Tracers with Quantitative Microbial Risk Assessment

“…Surrogates for exposure to respiratory aerosols include tracer gases − and solid particles, , though tracer gases do not simulate particle evaporation, transport, and removal. Solid particle tracers and particle mass concentration monitoring can indicate how aerosols are dispersed and removed, though these techniques do not simulate the changes in composition and size distribution that respiratory aerosols undergo following emission and evaporation. − Using an aerosol tracer solution with a composition comparable to that of mucosalivary fluid, it is possible to emulate the physicochemical changes that occur during respiratory aerosol emission and transport.…”

The Control of Metabolic CO2 in Public Transport as a Strategy to Reduce the Transmission of Respiratory Infectious Diseases

“…To overcome these hurdles, the CO 2 level has been suggested as an indirect indicator of respiratory infectious diseases’ transmission [ 22 ]. CO 2 is co-expired with bioaerosols that may contain SARS-CoV-2 in infected people [ 28 , 29 , 30 ]. Its quantification provides an idea of indoor air renewal and establishes the risk of infection as it depends on the viral load [ 31 ].…”

“…Despite the ventilation rates being known to influence the concentration of microorganisms in the environment [ 32 ], the increase in the exhalation rate of aerosols depending on CO 2 has been poorly explored [ 30 ]. The concentration of airborne particles and the level of CO 2 cannot be directly related due to a disparity between the bioaerosols generated and the respiratory activity [ 28 ]. For example, aerosol generation during forced vocalization or coughing is not comparable to emission rates during respiration [ 33 ].…”

Tempo-spatial infection risk assessment of airborne virus via CO2 concentration field monitoring in built environment

“…In coping with these issues, CO 2 from occupants exhalation was widely utilized as a feasible index to assess indoor ventilation performance [ 23 , 24 ] and has been suggested as an appropriate airborne disease infection risk proxy in buildings [ 25 , 26 ]. After exhaled by infector(s) during breathing, speaking, coughing and sneezing, virus-attached droplet nuclei with aerodynamic diameter below 10 μm was dispersed in the built environment with airflow.…”

“…Meanwhile, CO 2 was also exhaled by infector(s) continuously. According to the chamber study of Kappelt [ 25 ], the measured concentrations of PM10 and CO 2 kept increasing linearly in the 2 m 3 chamber for 10 min with participants’ exhalation. Participants released 6210 ± 5630 particles and 143 ± 29 ppm CO 2 per minute.…”