The Impact of CO2 Levels on Airborne Viral Loads

New research has indicated that keeping CO2 levels low can help reduce infectious airborne viral loads, particularly in spaces with limited ventilation. The study, focusing on the pathogen responsible for COVID-19, has significant implications for minimizing the risk of virus transmission. According to University of Bristol chemist Allen Haddrell, opening a window could be more effective than previously believed, especially in crowded and poorly ventilated areas. Fresh air with lower CO2 concentrations can lead to a faster inactivation of the virus.

Haddrell and his colleagues utilized a new technique called Controlled Electrodynamic Levitation and Extraction of Bioaerosol onto a Substrate (CELEBS) to measure the impact of temperature, relative humidity, and different gas concentrations on suspended virus particles. The study revealed that the stability of the SARS-CoV-2 virus is directly affected by CO2 levels in the air. While atmospheric CO2 concentrations are currently around 400 parts per million (ppm), they can reach up to 3,000 ppm in crowded indoor spaces. Under elevated concentrations, the number of viral particles that remain infectious can be significantly higher compared to outdoor air.

Haddrell explained that the high pH of exhaled droplets containing the SARS-CoV-2 virus plays a crucial role in the loss of infectiousness. When CO2 interacts with these droplets, it acts as an acid, causing the pH to become less alkaline. As a result, the virus within the droplets is inactivated at a slower rate. In highly crowded and poorly ventilated environments where CO2 levels exceed 5,000 ppm, the risk of virus transmission can escalate, potentially leading to super spreader events.

Interestingly, the study also found that different strains of SARS-CoV-2 exhibit varying patterns of stability in the air. For example, after 5 minutes, the viable viral particle concentrations were 1.7 times higher for the Omicron (BA.2) variant compared to the Delta variant. This suggests that there may be significant variability among different types of viral particles. Further research is needed to explore the relationship between CO2 levels and other viruses, but the findings hint at a possible explanation for the seasonality of many respiratory viruses.

As global warming leads to an increase in outdoor CO2 levels, projections suggest concentrations could exceed 700 ppm by the end of the century. Haddrell emphasized the importance of global net zero goals in light of these findings. Even slightly elevated levels of CO2, driven by climate change, can enhance the survival rate of viruses and increase the risk of transmission. The research serves as a scientific foundation for developing effective mitigation strategies that could save lives in future pandemics, according to University of Bristol physical chemist Jonathan Reid.