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Experimental study on isotope fractionation effects in visible photolysis of O 3 and in the O + O 3 odd oxygen sink reaction
Author(s) -
Früchtl Marion,
Janssen Christof,
Röckmann Thomas
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd022944
Subject(s) - photodissociation , fractionation , isotope fractionation , mass independent fractionation , equilibrium fractionation , chemistry , isotope , kinetic isotope effect , analytical chemistry (journal) , oxygen isotope ratio cycle , stable isotope ratio , ozone , chemical reaction , isotope analysis , photochemistry , environmental chemistry , chromatography , deuterium , geology , organic chemistry , physics , quantum mechanics , oceanography
Investigation of isotope effects in ozone (O 3 ) photolysis and its contribution to the overall ozone isotope composition is difficult since photolysis always leads to secondary O 3 formation and O 3 decomposition by reactions with O( 3 P). Here we use a large excess of carbon monoxide (CO) as O( 3 P) quencher to suppress O( 3 P) + O 3 . This allows disentangling the isotope effects in photolysis and chemical removal when the data are evaluated with a kinetic model. The largest systematic uncertainty arises from an unidentified O 3 removal reaction, which is responsible for an unaccounted 20% of the total removal rate. Assuming no isotope fractionation in this reaction, we find18 ε O 3 + h ν = ( 16 J / 18 J − 1) = −16.1 (±1.4)‰ and17 ε O 3 + h ν = −8.05 (±0.7)‰ for O 3 photolysis and18 ε O + O 3 = ( 16 k / 18 k − 1) = −11.9 (±1.4)‰ and17 ε O + O 3 = −5.95 (±0.7)‰ for chemical removal via O( 3 P) + O 3 . Allowing for isotope fractionation in the unidentified reaction results in lower fractionation values for photolysis and higher fractionations for chemical removal. Several fractionation scenarios are examined, which constrain the fractionation in photolysis to18 ε O 3 + h ν > −9.4‰ and17 ε O 3 + h ν > −4.7‰ and in the chemical removal to18 ε O + O 3 < −18.6‰ and17 ε O + O 3 < −9.3‰. Both fractionations are thus significant and of similar magnitude. Because our measurements are dominated by photolysis in the peak region of the Chappuis band, isotope fractionation of atmospheric O 3 by visible photons should also be in the same range. The isotope fractionation factor for O + O 3 directly bears on ozone chemistry in the lower thermosphere.