Temporal variations of the atmospheric nitrous oxide concentration and itsδ15N andδ18O for the latter half of the 20th century reconstructed from firn air analyses

[1] 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 δ15N 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 δ18O. 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.