Time-Resolved Photochemical Dynamics of Pyruvic Acid in Aqueous Solutions
MIN-HSIEN (TONY) KAO, Conlan Broderick, Jim Walker, Andrew J. Orr-Ewing, Bryan R. Bzdek, University of Bristol
Abstract Number: 139
Working Group: Aerosol Chemistry
Abstract
Pyruvic acid is an important component of secondary organic aerosol and arises from atmospheric oxidation of isoprene. The photochemistry of pyruvic acid differs significantly at the air-water interface compared to bulk solution or the gas phase. Absorption of UVA radiation and subsequent photoexcitation lead to dimerization and oligomerization processes in water. However, detailed reaction dynamics for this process have not yet been reported. In this study, we explore the photochemical reaction dynamics of pyruvic acid within bulk aqueous solutions across picosecond to microsecond timescales at an excitation wavelength of 345 nm using advanced spectroscopic techniques, including time-correlated single photon counting (TCSPC) and transient absorption spectroscopy (TAS). TCSPC allows measurement of fluorescence lifetimes with ~100-picosecond time resolution, whereas TAS allows observation of excited state absorption and kinetics with sub-picosecond time resolution.
Investigations of fluorescence lifetimes using TCSPC reveal a consistent lifetime (~4.5 ns) for the first excited state (S1) of pyruvic acid, indicating negligible interaction with the ground-state to form a dimer. Contrastingly, TAS experiments unveil the formation and decay of triplet state pyruvic acid, with kinetics varying with pyruvic acid concentration. These concentration-dependent kinetics suggest the triplet state plays an important role in dimerization reactions. We will also describe ongoing efforts to explore the photochemical dynamics of pyruvic acid within aqueous droplets. Individual picoliter droplets are collimated in a linear quadrupole electrodynamic balance and then spectroscopically interrogated using time-resolved techniques. The results of these picoliter droplet experiments will shed light on the photochemical dynamics of pyruvic acid in microcompartments and will allow comparisons to bulk phase studies.