Non-OH-driven liquid-phase chemistry in water microdroplets

Water microdroplets containing organic and fluorinated compounds, such as formate, perfluorooctanoic acid (PFOA) and triflic acid, were exposed to a radiofrequency glow discharge plasma with a droplet residence time on the order of milliseconds. Triflic acid remained unaffected by any plasma condition while >75% decomposition of formate and PFOA could be achieved. In situ hydroxyl (OH)-laser-induced fluorescence measurements near the droplets confirmed that the conversion was independent of the OH flux to the droplet. A series of control experiments suggest that the contribution of vacuum UV photons in such decomposition of aqueous compounds can be significant for He and He + 17% Ar plasmas and can also explain unexpected decomposition trends as a function of droplet residence time in the plasma.

Automated summary

Water microdroplets containing organic and fluorinated compounds were exposed to a radiofrequency glow discharge plasma, resulting in significant decomposition of formate and perfluorooctanoic acid, but no significant effect on triflic acid. In situ measurements confirmed that the conversion was independent of the OH flux to the droplet. Control experiments suggest that vacuum UV photons play a significant role in the decomposition process and can explain unexpected trends.