biostudies-literatureZheng GNational Natural Science Foundation of ChinaMax-Planck-Gesellschaft12571-12582https://www.ebi.ac.uk/biostudies/studies/S-EPMC10469486biostudies-literatureUnknown57(34)Acidity is one central parameter in atmospheric multiphase reactions, influencing aerosol formation and its effects on climate, health, and ecosystems. Weak acids and bases, mainly CO₂, NH₃, and organic acids, are long considered to play a role in regulating atmospheric acidity. However, unlike strong acids and bases, their importance and influencing mechanisms in a given aerosol or cloud droplet system remain to be clarified. Here, we investigate this issue with new insights provided by recent advances in the field, in particular, the multiphase buffer theory. We show that, in general, aerosol acidity is primarily buffered by NH₃, with a negligible contribution from CO₂ and a potential contribution from organic acids under certain conditions. FoEnvironmental science & technologyRole of Carbon Dioxide, Ammonia, and Organic Acids in Buffering Atmospheric Acidity: The Distinct Contribution in Clouds and Aerosols.PMC1046948622188102Zheng GSu HCheng YfalseRole of Carbon Dioxide, Ammonia, and Organic Acids in Buffering Atmospheric Acidity: The Distinct Contribution in Clouds and Aerosols.Acidity is one central parameter in atmospheric multiphase reactions, influencing aerosol formation and its effects on climate, health, and ecosystems. Weak acids and bases, mainly CO₂, NH₃, and organic acids, are long considered to play a role in regulating atmospheric acidity. However, unlike strong acids and bases, their importance and influencing mechanisms in a given aerosol or cloud droplet system remain to be clarified. Here, we investigate this issue with new insights provided by recent advances in the field, in particular, the multiphase buffer theory. We show that, in general, aerosol acidity is primarily buffered by NH₃, with a negligible contribution from CO₂ and a potential contribution from organic acids under certain conditions. Fo2023-01-01T00:00:00Z2023 Aug2025-04-19T20:07:02.296Z2025-04-19T20:07:02.296ZS-EPMC104694863759965110.1021/acs.est.2c09851