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Twilight observations suggest unknown sources of HO x
Author(s) -
Wennberg P. O.,
Salawitch R. J.,
Donaldson D. J.,
Hanisco T. F.,
Lanzendorf E. J.,
Perkins K. K.,
Lloyd S. A.,
Vaida V.,
Gao R. S.,
Hintsa E. J.,
Cohen R. C.,
Swartz W. H.,
Kusterer T. L.,
Anderson D. E.
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl900255
Subject(s) - solar zenith angle , stratosphere , wavelength , twilight , zenith , scattering , photodissociation , flux (metallurgy) , excited state , excitation , physics , atomic physics , absorption (acoustics) , analytical chemistry (journal) , materials science , astrophysics , optics , chemistry , atmospheric sciences , photochemistry , astronomy , quantum mechanics , chromatography , metallurgy
Measurements of the concentrations of OH and HO 2 (HO x ) in the high‐latitude lower stratosphere imply the existence of unknown photolytic sources of HO x . The strength of the additional HO x source required to match the observations depends only weakly on solar zenith angle (SZA) for 80° < SZA < 93°. The wavelengths responsible for producing this HO x must be longer than 650 nm because the flux at shorter wavelengths is significantly attenuated at high SZA by scattering and absorption. Provided that the sources involve only a single photon, the strength of the bonds being broken must be < 45 kcal mole −1 . We speculate that peroxynitric acid (HNO 4 ) dissociates after excitation to an unknown excited state with an integrated band cross section of 2‐3 × 10 −20 cm² molecule −1 nm (650 < λ < 1250 nm).