Elevated CO2 concentrations in the atmosphere limit the degree the equilibrium goes right. Thus, excess CO2 will affect the maximum pH the aerosol reaches. The virus is sensitive to the pH in this region (>10); any subtle change in pH can have a large effect in aerostability.
Implications: if the high pH of the respiratory aerosol is driving the loss of viral infectivity, it means that any increase in the conc of CO2 must have an effect of viral aerostability. The question becomes, will a difference be observable at CO2 conc in the real world?
We used a levitation/sampling technology we developed, called CELEBS (Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate), to probe the survival of different SARS-CoV-2 variants (Del+Omi) in mimics of exhaled particles in different conditions.
When compared to the Delta variant, the Omicron variant is more stable in a highly alkaline solution (pH 11). This relationship further supports our hypothesis presented in our previous publications that the high pH of respiratory aerosol is driving the loss of viral infectivity.
Omicron (BA.2) was found to be more aerostablethan the Delta variant when the humidity was high. In our previous study, we found that as the virus evolved, it had lost aerostability. This is the first time we’ve recorded an increase.
Omicron was also found to be more aerostablethan the Delta variant across a broad range of humidities. Perhaps this played a role in Omicron rising to prominence?
We levitated the Delta variant in air that had various levels of CO2 and measured the infectivity. Any increase in the concentration of CO2 was found to result in an increase the virus’s aerostability. At higher concentrations, the difference became more significant.
It has become popular to use CO2 monitors to estimate risk. This is based upon the idea that the CO2 informs about how well a space is ventilated. From our study, the results show that the levels of the CO2 will also inform about how long the virus remains infectious in the air.
A moderate increase in the concentration of CO2 dramatically affected the decay dynamics. Changes in CO2 concentrations resulted in a completely different decay profile, where a difference in aerostability was observed within as little as 30 seconds, and throughout.
This data shows that the concentration of CO2 has a dramatic effect on how the aerosolized viral load will accumulate. Over longer periods of time at high CO2, the rate in which the virus becomes inactivated gets slower (after 20 mins only a subtle change in viral infectivity)
In terms of total aerosolized viral load, this means that after 40 minutes, more than 10x the amount of virus remains infectious in the air as a result of an increase in CO2 concentration. This will have a massive effect on the risk of transmission in a poorly ventilated space.
Increased concentrations of CO2 effected virus aerostability across a broad range of humidity. Below a humidity of 90%, the increase in CO2 roughly doubled the amount of virus that remained infective. This suggests that CO2 is more important than RH on aerosolized viral spread.