Accelerated Zymonic Acid Formation from Pyruvic Acid at the Interface of Aqueous Nanodroplets

Area of Science:

• Atmospheric Chemistry
• Physical Chemistry
• Chemical Kinetics

Background:

• The role of interfaces in chemical reactions is crucial for understanding processes in confined environments.
• Pyruvic acid (PA) condensation to zymonic acid (ZA) is a slow reaction in bulk solutions.
• Submicron aerosols represent unique micro-environments where interfacial effects can dominate reactivity.

Purpose of the Study:

• To investigate the influence of the liquid interface on reaction kinetics within small compartments.
• To quantify the formation rate of zymonic acid (ZA) in submicron aerosols.
• To elucidate the mechanisms behind accelerated ZA formation in aerosol phases.

Main Methods:

• Utilized mass spectrometry to measure ZA formation kinetics in submicron aerosols (average radius = 240 nm).
• Employed a kinetic model to simulate experimental results and validate findings.
• Compared reaction rates in aerosols versus bulk solutions.

Main Results:

• ZA formation in submicron aerosols occurred in minutes, compared to days in bulk solutions.
• An apparent interfacial reaction rate coefficient (k_i) of (0.9 ± 0.2) × 10^-3 M^-1 s^-1 was determined.
• Simulations indicated that PA surface activity and enhanced interfacial reaction rates drive accelerated ZA formation.

Conclusions:

• The condensation reaction of PA to ZA occurs predominantly at the aerosol-solution interface.
• The interfacial reaction rate coefficient is enhanced by approximately 4 orders of magnitude compared to bulk solutions.
• Liquid interfaces significantly mediate and accelerate chemical reactivity in small aerosol compartments.