EC-05. Aqueous Pyruvic Acid: Insights from Surface and Bulk Vibrational Spectroscopy
One of the major challenges in accurately modeling Earth’s climate is the role of aerosols. These particles affect how much sunlight is absorbed in the atmosphere through their own optical properties and also play a key role in cloud formation. Aqueous aerosols are known to have an organic component and larger hydrophobic organics will be preferentially located at the water-air interface. Organic compounds at the surface of aerosol particles will affect both their optical properties and cloud formation. Reactions that lead to larger organic molecules may also be a pathway to secondary organic aerosol formation. We have studied the biogenic organic acid pyruvic acid in aqueous environments. When in water, this compound establishes an equilibrium with its gem diol which had distinct properties from the keto form. Using the complementary techniques of infrared and Raman spectroscopies along with quantum chemical calculations, we have identified the presence of both the keto and the gem diol forms in aqueous solutions. Bulk solutions were studied with attenuated total reflection infrared spectroscopy (ATR-IR), while the surface of water was observed via infrared reflection-absorption spectroscopy (IRRAS). Water droplets were observed with Raman microscopy; focusing on droplet edges was used to probe the surface region. Our spectra show that not only is the diol ubiquitous in solution, but it is also present at the water surface. The implications for organic reactivity in aqueous aerosols in Earth’s atmosphere will be discussed.