HR: 0800h
AN: A21C-0865    [Abstracts]
TI: Photochemical Production and Release of NO2 from Nitrate-Doped Water Ice
AU: * Boxe, C
EM: boxe@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories, Pasadena, CA 91125 United States
AU: Colussi, A
EM: ajcoluss@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories, Pasadena, CA 91125 United States
AU: Hoffmann, M
EM: mrh@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories, Pasadena, CA 91125 United States
AU: Murphy, J
EM: j.g.murphy@uea.ac.uk
AF: University of California, Berkeley, Department of Chemistry and Department of Earth and Space Sciences, Berkeley, CA 94270 United States
AU: Wooldridge, P
EM: pjwool@Socrates.berkeley.edu
AF: University of California, Berkeley, Department of Chemistry and Department of Earth and Space Sciences, Berkeley, CA 94270 United States
AU: Bertram, T
EM: tbertram@berkeley.edu
AF: University of California, Berkeley, Department of Chemistry and Department of Earth and Space Sciences, Berkeley, CA 94270 United States
AU: Cohen, R
EM: cohen@cchem.berkeley.edu
AF: University of California, Berkeley, Department of Chemistry and Department of Earth and Space Sciences, Berkeley, CA 94270 United States
AB: Temperature-programmed NO₂ emissions from irradiated, frozen NaNO₃ aqueous solutions were monitored as function of nitrate concentration and heating rate H, above - 30 °C. Emissions increase nonmonotonically with temperature, displaying transitions suggestive of underlying metamorphic transformations. Thus, NO₂ emissions surge at ca. - 8 °C in frozen [NO₃^-] > 200 μM samples warmed at H = 0.70 °C min^-1 under continuous irradiation, and also in the dark from samples that had been photolyzed at - 30 °C. The amounts of NO₂ released in individual thermograms, σ_N, increase less than linearly with [NO₃^-] or the duration of experiments, revealing significant losses of photogenerated NO₂. The actual σ_N proportional to [NO₃^-]^1/2 dependence (at constant H) is consistent with NO₂ hydrolysis: 2NO₂ + H₂O producing NO₃^- + NO₂^- + 2H⁺, overtaking NO₂ desorption, even below the eutectic point (- 18 °C for aqueous NaNO₃). The increasingly larger losses detected in longer experiments (at constant [NO₃^-]) are ascribed to secondary photolysis of trapped NO₂. The relevance of present results to the interpretation of polar NO₂ measurements is briefly analyzed.
UR: http://www.its.caltech.edu/~boxe
DE: 9900 CORRECTIONS
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005