Temporal variations of the atmospheric nitrous oxide concentration and its <i>δ</i>¹⁵N and <i>δ</i>¹⁸O for the latter half of the 20th century reconstructed from firn air analyses

Abstract

Histories of atmospheric N 2 O concentration and its δ 15 N and δ 18 O were reconstructed for the period 1952–2001 on the basis of the analyses of firn air collected at the North Greenland Ice Core Project (NGRIP), Greenland, and Dome Fuji and H72, Antarctica. The N 2 O concentration increased from 290 ppbv in 1952 to 316 ppbv in 2001, which agrees well with the results from atmospheric observations and polar ice core analyses. The δ 15 N and δ 18 O showed a secular decrease, the respective values being 8.9 and 21.5‰ in 1952 and 7.0 and 20.5‰ in 2001. Their rates of change also varied, from about −0.02‰ yr −1 in the 1950s to about −0.04‰ yr −1 in 1960–2001 for δ 15 N, and from about 0‰ yr −1 to −0.02‰ yr −1 for δ 18 O. The isotopic budgetary calculations using a two‐box model indicated that anthropogenic N 2 O emission from soils played a main role in the atmospheric N 2 O increase after industrialization, as well as that the average isotopic ratio of anthropogenic N 2 O has potentially been changed temporally.