Temporal and latitudinal distributions of stratospheric N₂O isotopomers

Abstract

[1] Temporal and latitudinal variations of vertical profiles of N 2 O isotopomers were observed in the stratosphere over Japan (39°N, 142°E), Sweden (68°N, 20°E) O were nearly constant in the lower stratosphere (less than $22 km) but increased at higher altitudes ($22-35 km) while showing seasonal and latitudinal differences. Enrichment factors during the photolysis and photo-oxidation of N 2 O were also obtained in laboratory experiments and compared with those observed. We found that in the higher-altitude region (1) fractionation of the isotopomers is mainly determined by photolysis, but is also affected by physical processes, (2) subsidence of air masses in the winter polar vortex induces the intrusion of an upper stratospheric air mass depleted in N 2 O, and (3) decay of the vortex in the local spring leads to rapid horizontal advection of midlatitude air masses. At lower altitudes, isotopomer ratios are determined by photolysis, photo-oxidation, and the mixing of air masses within the stratosphere or between the stratosphere and the troposphere. Secular trend of isotopomer profiles was not detectable over Japan during 11 years. Assuming that the lower stratospheric air over midlatitudes is exchanged with the troposphere, isotopomer ratios of the N 2 O ''back-flux'' from the stratosphere were estimated. These values can be used in the isotopomeric mass balance model to constrain the global N 2 O budget.

Probing stratospheric transport and chemistry with new balloon and aircraft observations of the meridional and vertical N<sub>2</sub>O isotope distribution

“…The Delta Plus XP allows simultaneous registering of mass-to-charge ratios 30, 31, 44, 45, and 46, which has the advantage of requiring only a single extraction/injection of sample for analysis. The reproducibility for a 2 nmol N 2 O sample was about 0.15‰ for (Park et al, 2004;Toyoda et al, 2004).…”

“…The paper by Toyoda et al (2004) also contains the data from the earlier two papers by the same principal authors. All but the Fourier transform infrared-spectra (FTIR) of were analyzed by isotope ratio mass-spectrometry (IRMS) of discrete whole-air samples, either obtained by aircraft (Park et al, 2004) or from balloon platforms.…”

“…The new analytical techniques were used for further stratospheric measurements, as evidenced by six publications Park et al, 2004;Röckmann et al, 2001;Toyoda et al, 2001Toyoda et al, , 2004Yoshida and Toyoda, 2000). The paper by Toyoda et al (2004) also contains the data from the earlier two papers by the same principal authors.…”

“…Analytical advances in the late 1990s then allowed the position-dependent measurement of the nitrogen isotope distribution between the terminal and central nitrogen atoms in N 2 O (Brenninkmeijer and Röckmann, 1999;Esler et al, 2000;Toyoda and Yoshida, 1999). The new techniques were immediately adopted for extensive laboratory measurements of kinetic isotope effects during photolysis (summarized in Kaiser et al, 2003b andvon Hessberg et al, 2004) and the reaction of N 2 O with O( 1 D) (Kaiser et al, 2002a;Toyoda et al, 2004). Our present understanding of these isotope effects can be considered to be very good.…”

Site selective real-time measurements of atmospheric N<sub>2</sub>O isotopomers by laser spectroscopy

“…The bulk nitrogen δ value (δ 15 N bulk = (δ 15 N α + δ 15 N β )/2) of tropospheric N 2 O is enriched by 6.3 ± 0.3 ‰ to 6.72 ± 0.12 ‰, depending on the sampling location and time (Kaiser et al, 2003;Park et al, 2004;Röckmann and Levin, 2005;Toyoda et al, 2004), with a strong site preference (SP = δ 15 N α − δ 15 N β ) of 18.7 ± 2.2 ‰ for the central nitrogen atom (Yoshida and Toyoda, 2000). Temporal trends in the N 2 O isotopic composition from firn air, ice core and archived air sample measurements indicate a year to year decrease in δ 15 N bulk of 0.04 ‰ yr −1 , confirming substantial emissions of isotopically depleted N 2 O (Bernard et al, 2006;Ishijima et al, 2007;Röckmann and Levin, 2005).…”