Fig. 5.

The role of pH in SARS-CoV-2 airborne loss of infectivity. (A) Bulk % infectivity of SARS-CoV-2 (B.1.351) after a 30-min incubation in DMEM 2% FBS altered to either pH 9 (purple datapoints) or 11 (green datapoints), diluted back into neutral media and plated onto cells every 10 min. Datapoints are the mean of three measurements for pH 11 and five measurements for pH 9, with error bars showing the standard error. (B) The pH changes that tissue culture media (in this case DMEM) underwent when exposed to open air. DMEM was left in an open petri dish or 50-mL tube both with and without HEPES and the initial pH (blue bar) and the pH after 20 min (orange bar) was measured. The same measurement was carried out using thin layers of DMEM that were allowed to evaporate to 10% of their original volume over the course of 24 h (labelled fully evaporated). (C) The 5-min levitations were carried out with SARS-CoV-2 (B.1.351) at 90% RH with varying CO₂ concentrations mixed into the gas flow. Bars show the mean of 15 measurements for 0% CO₂, 16 measurements for 5% CO₂, and 6 measurements for 10% CO₂ with the error bars showing the standard error. *P < 0.03 between 0% and 5% CO₂.