Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk

Abstract

An improved understanding of the underlying physicochemical properties of respiratory aerosol that influence viral infectivity may open new avenues to mitigate the transmission of respiratory diseases such as COVID-19. Previous studies have shown that an increase in the pH of respiratory aerosols following generation due to changes in the gas-particle partitioning of pH buffering bicarbonate ions and carbon dioxide is a significant factor in reducing SARS-CoV-2 infectivity. We show here that a significant increase in SARS-CoV-2 aerostability results from a moderate increase in the atmospheric carbon dioxide concentration (e.g. 800 ppm), an effect that is more marked than that observed for changes in relative humidity. We model the likelihood of COVID-19 transmission on the ambient concentration of CO2, concluding that even this moderate increase in CO2 concentration results in a significant increase in overall risk. These observations confirm the critical importance of ventilation and maintaining low CO2 concentrations in indoor environments for mitigating disease transmission. Moreover, the correlation of increased CO2 concentration with viral aerostability need to be better understood when considering the consequences of increases in ambient CO2 levels in our atmosphere.

Review of factors affecting virus inactivation in aerosols and droplets

“…Haddrell et al [65] demonstrated that the introduction of HNO 3 to the system had minimal effects on virus stability, contrary to the prediction of Luo et al [55]. Haddrell et al [65] further demonstrated that increasing the gaseous CO 2 concentration increased the stability of SARS-CoV-2 in aerosols [74]. Results align with a study on SARS-CoV-1 that observed infectivity was sensitive to both acidic conditions (pH 1-3) and alkaline conditions (pH 12-14) but stable at pH 5-9 [63].…”

“…Thus, plots of virus infectivity as a function of time may appear to have a discontinuity between the first and second phases of decay if ambient RH is below the efflorescence RH. Haddrell et al [74] described three phases of decay: a lag phase, a dynamic phase and a slow decay phase, where the dynamic phase corresponds to efflorescence or other rapidly changing conditions in a particle.…”

“…elevated viability at low and high RHs, with decreased viability at medium RH), and (iv) no difference in viability as a function of RH. Because measurements of infectivity are usually collected after many minutes to hours in experiments, these results usually incorporate multiple phases of decay (§5.3), although one older study and some recent studies include sufficient temporal resolution to distinguish biphasic or triphasic decay [ 10 , 13 , 21 , 71 , 74 ]. Typically, researchers have observed increasing infectivity with increasing RH in non-enveloped viruses, for example poliovirus [ 13 , 24 , 52 ], foot-and-mouth disease virus (FMDV) [ 111 , 112 ] and rhinovirus [ 102 , 113 ], and a U-shaped trend in infectivity among enveloped viruses, for example influenza virus [ 30 , 43 , 114 ], vesicular stomatitis virus (VSV) [ 77 , 115 ] and SARS-CoV-2 [ 6 , 71 ] ( figures 1 a–c and 2 , electronic supplementary material, figures S2a–c and S3a,b).…”

“…Physicochemically, it is at equilibrium, but virus decay may continue. Furthermore, a rapid loss in virus infectivity of approximately 50% has been observed at the time of efflorescence [ 10 , 21 , 65 , 66 , 74 ]. Thus, plots of virus infectivity as a function of time may appear to have a discontinuity between the first and second phases of decay if ambient RH is below the efflorescence RH.…”

“…Variants of SARS-CoV-2 in the studies include WA1/2020, REMRQ0001, Delta, England-2, O.S. and BetaCoV-2020[10,21,51,55,[61][62][63][64][67][68][69][70][71][72][73][74][75][76][77][78][79][80]. Additional network diagrams at low and medium RHs are available in electronic supplementary material, figureS3.Figure created using ConceptDraw DIAGRAM, by CS Odessa.…”