Time-resolved Photochemistry of Pyruvic Acid
CONLAN BRODERICK, Min-Hsien (Tony) Kao, Bryan R. Bzdek, Andrew J. Orr-Ewing, University of Bristol
Abstract Number: 64
Working Group: Aerosol Chemistry
Abstract
Pyruvic acid (PA), the simplest α-keto acid and a key oxidation product of isoprene, plays a significant role in the formation of secondary organic aerosols (SOAs)—a major component of fine particulate matter — with implications for both air quality and climate. As a semi-volatile compound, PA partitions between the gas and condensed phases and exhibits environment-dependent photochemistry. In complex aerosol matrices, which can include supersaturated solute states, understanding the solvent-dependent photodynamics of PA is essential for accurately assessing its atmospheric behavior.
This study investigates the excited-state dynamics of PA in bulk water and acetonitrile solutions using two ultrafast spectroscopy techniques: time-correlated single photon counting (TCSPC) and transient electronic absorption spectroscopy (TEAS). TCSPC measurements reveal longer fluorescence lifetimes in acetonitrile (7.5 ns) than in water (4 ns), indicating solvent-mediated differences in the relaxation dynamics. TEAS spectra, obtained for PA in water/acetonitrile following 345 nm excitation (a near-UV wavelength chosen to be relevant to atmospheric conditions) show evolving excited-state absorption (ESA) features, with kinetic analysis identifying three time constants: 400 ps, 7.5 ns, and 110 ns. Notably, signatures of a transient species (tentatively, Tâ‚‚ state population) appear in acetonitrile TEAS measurements but are absent in water.
The bulk-phase results highlight the critical influence of solvent environment on the excited-state behavior of PA and suggest implications for its reactivity and lifetime in atmospheric condensed aerosol phases. Ongoing work is extending these studies to 30-micron aqueous droplets using TCSPC, aiming to better replicate the microenvironments of atmospheric aerosols and explore the air–water interfacial chemistry. These droplet-phase experiments will give new insights into how confinement and surface effects modulate the photochemical pathways of PA, offering a valuable complement to the bulk solution measurements.