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Acidic pH inactivation of SARS-CoV-2 in exhaled breath and expectoration (ApHiCoV)

English title Acidic pH inactivation of SARS-CoV-2 in exhaled breath and expectoration (ApHiCoV)
Applicant Peter Thomas
Number 196729
Funding scheme Special Call on Coronaviruses
Research institution Institut für Atmosphäre und Klima ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Other disciplines of Environmental Sciences
Start/End 01.07.2020 - 31.08.2022
Approved amount 292'450.00
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All Disciplines (2)

Other disciplines of Environmental Sciences
Physical Chemistry

Keywords (6)

inactivation mechanism; expiratory aerosol; electrodynamic balance; biophysical aerosol model; pH; respiratory fluid

Lay Summary (German)

Als medizinische Intervention und Krankheitsmanagement für COVID-19 erforscht das SNF-Projekt ApHiCoV die Inaktivierung von Corona-Viren in ausgeatmeten Partikeln mit Hilfe von Essigsäuredämpfen
Lay summary

Ein saures Milieu (niedrige pH-Werte) ist wirksam gegen Viren, die von einer Lipidhülle umgeben sind, wie der neuartige Corona-Virus.  Die Virushülle kann bei einem niedrigen pH-Wert zerstört werden, was den Virus inaktiviert, ähnlich wie beim Pasteurisieren.  ApHiCoV erforscht die Möglichkeit, gasförmige Essigsäure in Raumluft auf Konzentrationen anzureichern, die zwar für Personen im Raum noch unschädlich sind, aber ausreichen, um die Viren in Aerosolpartikeln, Tröpfchen und auf verschmutzten Gegenständen zu inaktivieren.  Ziel ist, den pH-Wert von ausgeatmeten Partikeln so weit zu senken, dass das Risiko einer Übertragung von COVID-19 wirksam vermindert wird.

Direct link to Lay Summary Last update: 11.06.2020

Responsible applicant and co-applicants


Project partner

Associated projects

Number Title Start Funding scheme
189939 Infectivity of influenza viruses in expiratory aerosols under ambient temperatures and humidities (IVEA) 01.06.2020 Sinergia


Acidic pH inactivation is known to be effective against enveloped viruses, such as SARS-CoV-2, which exposed to a low pH will denature spontaneously. Similar to pasteurization, viral reduction by chemical treatment at pH ~< 4, is thought to be achieved by destroying the lipid envelope, which results in an effective inactivation of the viruses. Several previous studies, e.g. for avian influenza virus and Bovine diarrhoea virus , suggest an exponential decay of active virus titer, exp(-t/t), with mean lifetimes t = 3-4 minutes upon exposure to pH = 4 (i.e. titer reductions by 99 % after less than 15 minutes). Similar investigations for SARS-CoV-2 are still lacking. ApHiCoV will investigate the possibility to use gaseous acetic acid (CH3COOH) in room air, as an easy-to-apply measure, in order to lower the pH of exhalation aerosol, expectorated droplets and contaminated contact sur-faces, and thereby to effectively mitigate the risk of transmission of enveloped viruses such as SARS-CoV-2. To this end we will- determine the thermodynamics of airway lining fluid and mucus and molecular diffusion processes therein, in particular with respect to solubility and diffusivity of CH3COOH;- investigate the uptake kinetics of CH3COOH into airway lining fluid and mucus of micron-sized aerosol particles, millimeter-sized droplets and contaminated planar contact surfaces;- consider the buffering by ammonium (NH4+ ), i.e. its neutralization by CH3COOH in the exhaled or expectorated substance as well as the loss of ammonia (NH3) to the gas phase of the indoor air;- determine the kinetics of pH-change (within milliseconds to minutes) inside the exhaled aerosol particles and expectorated drops subject to CH3COOH in the indoor air;- identify the target pH, i.e. the optimum acidity between being most efficient in virus inactivation, yet still acceptable for the health of the exposed individuals;- determine the pH-dependent inactivation kinetics of SARS-CoV-2 in the acidified airway lining fluid and mucus.These investigations will be performed experimentally in due consideration of biosafety and by thermodynamic and kinetic modelling. Experimental work will include the investigation of CH3COOH uptake kinetics of droplets in the 1-35 µm size regime by means of an electrodynamic balance, a direct determination of droplet pH for these droplets, and the measurement of active virus titer reduction in acidified airway lining fluid and mucus in a BSL-3 laboratory. Modeling work will apply a state-of-the-art thermodynamic and kinetic model applied in spherical and planar geometry for droplets and contaminated contact surfaces. We aim at answering the following questions:- Can rapid SARS-CoV-2 inactivation by pH-reduction be reached by applying indoor CH3COOH below the legal permissible exposure limit for 8-hour work-shifts, i.e. at concentrations below 10 ppmv?- Can such a pH-reduction even be reached by applying indoor CH3COOH below the odor threshold of unacclimatized individuals of ~1 ppmv? - If the results of this investigation are encouraging, could gaseous CH3COOH be used as disinfecting measure in hospitals?- Given CH3COOH application would be a cheap and easy-to-apply measure, allowing the inactivation of viruses in exhaled aerosol, in droplets and on all kinds of surfaces, could it potentially also be applied in other places in the public domain or in private houses?