The pH of aqueous aerosols, as well as cloud and fog droplets, has an important influence on the chemistry that takes place within these unique microenvironments. Utilizing conjugate acid/base pairs to infer pH changes, we investigate, for the first time, changes in aerosol pH upon droplet coalescence. In particular, we show that the pH within individual aqueous aerosol droplets that are ~8 μm in diameter can be titrated via droplet coalescence in an Aerosol Optical Tweezer (AOT). Using sulfate/bisulfate and carbonate/bicarbonate as model systems, the pH of trapped droplets is determined before and after introduction of smaller droplets containing a strong acid. The pH change upon coalescence of the acid within the trapped droplet is calculated using Specific Ion Interaction Theory (SIT). Furthermore, we show that the pH of an individual aerosol can be manipulated along a fairly wide range of pH values, paving the way for future studies requiring rigorous pH control of aqueous aerosol.

Titration of aerosol pH through droplet coalescence

2019 Fall National Meeting

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