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 delta N-15 and delta O-18 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 (NO)-O-2 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 delta N-15 and delta O-18 showed a secular decrease, the respective values being 8.9 and 21.5 parts per thousand in 1952 and 7.0 and 20.5 parts per thousand 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 delta N-15, and from about 0 parts per thousand yr(-1) to -0.02 parts per thousand yr(-1) for delta O-18. 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.