Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 3 2009 10.5194/acpd-9-13123-2009 http://www.atmos-chem-phys-discuss.net/9/13123/2009/ http://www.atmos-chem-phys-discuss.net/9/13123/2009/acpd-9-13123-2009.html http://www.atmos-chem-phys-discuss.net/9/13123/2009/acpd-9-13123-2009.pdf 13123 13153 2009-06-12 Evidence of the water-cage effect on the photolysis of NO₃^- and FeOH²⁺, and its implications for the photochemistry at the air-water interface of atmospheric droplets P. Nissenson D. Dabdub R. Das V. Maurino C. Minero D. Vione davide.vione@unito.it Dept. of Mechanical and Aerospace Engineering, University of California, Irvine, CA, USA Dipartimento di Chimica Analitica, Università degli Studi di Torino, Via P. Giuria 5, 10125 Torino, Italy Dept. of Chemical Engineering, Haldia Institute of Technology, ICARE complex, Haldia 721657, India Experiments are conducted to determine the photolysis quantum yields of nitrate, FeOH²⁺, and H₂O₂ in the bulk and at the surface layer of water. Results show that the quantum yields of nitrate and FeOH²⁺ are enhanced at the surface compared to the bulk due to a reduced water-cage surrounding the photo-fragments (^•OH+^•NO₂ and Fe²⁺+^•OH, respectively). However, no evidence is found for an enhanced quantum yield for H₂O₂ at the surface. The photolysis rate constant distribution within nitrate, FeOH²⁺, and H₂O₂ aerosols is calculated by combining the quantum yield data with Mie theory calculations of light intensity. Values for the photolysis rate constant of nitrate and FeOH²⁺ are significantly higher at the surface than in the bulk due to enhanced quantum yields at the surface. 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