Composition of firn air at the H72 ice core site, Antarctica

Histories of atmospheric N2O concentration and its d15N and d18O were reconstructed on the basis of the analyses of firn air collected at the H72, Antarctica. The N2O concentration increased from 297 ppbv in 1975 to 314 ppbv in 1998, which reasonably agrees with the results from atmospheric observations and polar ice core analyses. The d15N and d18O showed a secular decrease, the respective values being 8.2 and 45.1% in 1975 and 7.1 and 44.6% in 2001. The secularly decreasing trends reflect that anthropogenic N2O emission from soils played a main role in the atmospheric N2O increase after industrialization.