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Published May 27, 2008 | Published + Supplemental Material
Journal Article Open

Acidity enhances the formation of a persistent ozonide at aqueous ascorbate/ozone gas interfaces


The pulmonary epithelium, like most aerial biosurfaces, is naturally protected against atmospheric ozone (O3) by fluid films that contain ascorbic acid (AH2) and related scavengers. This mechanism of protection will fail, however, if specific copollutants redirect AH2 and O3(g) to produce species that can transduce oxidative damage to underlying tissues. Here, the possibility that the synergistic adverse health effects of atmospheric O3(g) and acidic particulate matter revealed by epidemiological studies could be mediated by hitherto unidentified species is investigated by electrospray mass spectrometry of aqueous AH2 droplets exposed to O3(g). The products of AH2 ozonolysis at the relevant air–water interface shift from the innocuous dehydroascorbic acid at biological pH to a C4-hydroxy acid plus a previously unreported ascorbate ozonide (m/z = 223) below pH {approx}5. The structure of this ozonide is confirmed by tandem mass spectrometry and its mechanism of formation delineated by kinetic studies. Present results imply enhanced production of a persistent ozonide in airway-lining fluids acidified by preexisting pathologies or inhaled particulate matter. Ozonides are known to generate cytotoxic free radicals in vivo and can, therefore, transduce oxidative damage.

Additional Information

© 2008 by The National Academy of Sciences of the USA. Freely available online through the PNAS open access option. Edited by Barbara J. Finlayson-Pitts, University of California, Irvine, CA, and approved February 28, 2008 (received for review November 13, 2007). Published online on May 16, 2008, 10.1073/pnas.0710791105. We thank C.D. Vecitis and J. Cheng for experimental assistance. S.E. is grateful to Prof. Yutaka Matsumi (Solar–Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan), Prof. Masahiro Kawasaki (Department of Molecular Engineering, Kyoto University, Kyoto, Japan), and the Japan Society for the Promotion of Science Research Fellowship for Young Scientists. This work was supported by National Science Foundation Grant ATM-0534990. Author contributions: A.J.C. designed research; S.E. performed research; M.R.H. contributed new reagents/analytic tools; S.E. and A.J.C. analyzed data; and S.E. and A.J.C. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/cgi/content/full/Supplemental0710791105/DCSupplemental.

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