Fractionation of N2O isotopomers in the stratosphere

Citation
S. Toyoda et al., Fractionation of N2O isotopomers in the stratosphere, J GEO RES-A, 106(D7), 2001, pp. 7515-7522
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Volume
106
Issue
D7
Year of publication
2001
Pages
7515 - 7522
Database
ISI
SICI code
Abstract
The vertical distribution of isotopomers of N2O ((NNO)-N-14-N-15-O-16, (NNO )-N-15-N-14-O-16, and (NNO)-N-14-N-14-O-18) in the lower and middle stratos phere was observed over Japan (39 degreesN, 142 degreesE) in 1999 using a b alloon-borne cryogenic sampler and ground-based mass spectrometry. The abun dance of the heavier isotopomers relative to (NNO)-N-14-N-14-O-16 increased with altitude, while the mixing ratio of N2O decreased due to photochemica l depletion. Maximum fractionation was observed at the highest altitude, 34 .5 km, where delta 15N(air)(alpha) (isotopomer ratio of center nitrogen), d elta 15N(air)(beta) (end nitrogen), and delta O-18(SMOW) were 144.1 parts p er thousand, 42.4 parts per thousand, and 119.0 parts per thousand, respect ively. The observed distribution is mostly accounted for by isotopic fracti onation during consumption processes, which is in accordance with reported simulation experiments and theoretical prediction for photolytic fractionat ion of N2O isotopomers. However, the apparent fractionation factors in the lower (< <similar to>24 km) and higher regions are different, which suggest s that (1) the fractionation factor for stratospheric photolysis may depend on altitude or latitude, (2) transport and mixing processes in the stratos phere can affect the vertical profile, and (3) the relative contribution of photolysis and photo-oxidation to total N2O sink is possibly dependent on altitude.