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Wavelength‐dependent isotope fractionation in visible light O 3 photolysis and atmospheric implications
Author(s) -
Früchtl Marion,
Janssen Christof,
Taraborrelli Domenico,
Gromov Sergey,
Röckmann Thomas
Publication year - 2015
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 - 10.1002/2015gl066219
Subject(s) - fractionation , photodissociation , wavelength , isotope fractionation , isotope , analytical chemistry (journal) , mass independent fractionation , absorption (acoustics) , visible spectrum , troposphere , materials science , chemistry , optics , photochemistry , physics , atmospheric sciences , optoelectronics , chromatography , quantum mechanics
The 17 O and 18 O isotope fractionation associated with photolysis of O 3 in the Chappuis band was determined using a broadband light source with cutoff filters at 455, 550, and 620 nm and narrowband light sources at 530, 617, and 660 nm. The isotope effects follow a mass‐dependent fractionation pattern (δ 17 O/δ 18 O = 0.53). Contrary to theoretical predictions, fractionations are negative for all wavelength ranges investigated and do not change signs at the absorption cross‐section maximum. Our measurements differ from theoretical calculations by as much as 34‰ in ε O 3 + h ν18 = ( 18 J / 16 J − 1). The wavelength dependence is also weaker than predicted. Photo‐induced fractionation is strongest when using a low‐wavelength cutoff at 620 nm with ε O 3 + h ν18 = −26.9(±1.4)‰. With decreasing wavelength, fractionation values diminish to ε O 3 + h ν18 = −12.9(±1.3)‰ at 530 nm. Results from an atmospheric model demonstrate that visible light photolysis is the most important tropospheric sink of O 3 , which thus contributes about one sixth to the ozone enrichment.