Photolysis of pyruvic acid in ice: Possible relevance to CO and CO2 ice core record anomalies

• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Guzmán; ice core
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.154.2620; http://people.seas.harvard.edu/~mig/JGR_2007.pdf

[1] The abnormal spikes detected in some CO and CO2 polar ice core records indicate persistent chemical activity in glacial ice. Since CO and CO2 spikes are correlated, and their amplitudes scale with reported CO/CO2 yields for the photolysis of dissolved natural organic matter, a common photochemical source is implicated. Given that sufficient actinic radiation is constantly generated throughout ice by cosmic muons (Colussi and Hoffmann, 2003), it remains to be shown that the photolyses of typical organic contaminants proceed by similar mechanisms in water and ice. Here we report that the photodecarboxylation of pyruvic acid (PA, an ubiquitous ice contaminant) indeed leads to the same products nearly as efficiently in both media. CO 2 is promptly released from frozen PA/H2O films upon illumination and continues to evolve after photolysis. By analogy with our studies in water (Guzmán et al., 2006b), we infer that 3 PA * reacts with PA in ice producing CH3C(O)C(O)O and (CH3 _C (OH)C(O)OH) radicals. The barrierless decarboxylation, CH3C(O)C(O)O!CH3C(O) +CO2, accounts for prompt CO2 emissions down to 140 K. Bimolecular radical reactions subsequently ensue in fluid molecular environments, both in water and ice, leading to metastable intermediates