Temporal variations of the atmospheric nitrous oxide concentration and its δ¹⁵N and δ¹⁸O for the latter half of the 20th century reconstructed from firn air analyses

Histories of atmospheric N₂O concentration and its δ¹⁵N and δ¹⁸O 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 N₂O 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 δ¹⁵ N and δ¹⁸O 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 δ¹⁵N, and from about 0‰ yr^-1 to -0.02‰ yr^-1 for δ ¹⁸O. The isotopic budgetary calculations using a two-box model indicated that anthropogenic N₂O emission from soils played a main role in the atmospheric N₂O increase after industrialization, as well as that the average isotopic ratio of anthropogenic N₂O has potentially been changed temporally.