Acids help against airborne viruses

Viruses such as SARS-CoV-2, influenza virus and others travel from person to person essentially by hitchhiking on aerosols. These are finely dispersed particles containing liquid suspended in the air that an infected person expels when coughing, sneezing, or simply exhaling, and can be inhaled by someone else.

That’s why it is generally seen as important to ventilate rooms effectively and filter indoor air: lowering aerosol particle concentrations in homes, offices and public transport vehicles can reduce the risk of infection.

How do suspended particles become acidic?

It’s not clear how long viruses in aerosols remain infectious. Some studies suggest that the humidity and temperature of the air may play a role in virus persistence. A factor that has been underestimated so far is the exhaled aerosols’ chemical composition, in particular its acidity and its interactions with the indoor air. Many viruses, such as influenza A virus, are acid-sensitive; exhaled aerosol particles can absorb volatile acids and other airborne substances, among them acetic acid, nitric acid or ammonia, from the indoor air, which in turn affects the acidity (pH) levels of the particles.

No research had yet been conducted on the effect the acidification of aerosols post exhalation has on the viral load they carry. Now a team of researchers from ETH Zurich, EPFL and the University of Zurich has investigated exactly that.

In a new study, they show for the first time how the pH of aerosol particles changes in the seconds and hours after exhalation under different environmental conditions. Further, they show how this impacts the viruses contained in the particles. The study has just been published in the journal Environmental Science & Technology.

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