Naohiro Yoshida

Temporal changes in the magnitude and geographic distribution of different sources of nitrous oxide (N 2 O) are not well constrained. To better understand the dynamics of N 2 O in the atmosphere over the last century, we have reconstructed the mole fraction, δ 15 N bulk , δ 18 O, and δ 15 N SP values of N 2 O from ice cores, firn air archives, and modern atmospheric samples. We have provided new firn air records from the Styx Glacier, Antarctica, and the North Greenland Eemian Ice drilling Project, and updated the firn air transport modeling of the published records. The composite reconstruction shows that the N 2 O growth rates were 0.26 ± 0.05, 0.15 ± 0.05 and 0.75 ± 0.01 ppb yr −1 during 1850–1930 (P1), 1931–1965 (P2) and 1966–2021 CE (P3), respectively. The temporal slope found in a linear least squares fit in δ 15 N bulk and δ 18 O were −0.010 ± 0.025 and −0.004 ± 0.031‰ yr −1 , −0.014 ± 0.013 and −0.009 ± 0.017‰ yr −1 , and −0.040 ± 0.013 and −0.022 ± 0.005‰ yr −1 during P1, P2 and P3 phases, respectively. Overall, a significant long‐term trend was not observed in δ 15 N SP data. Two‐box model calculations using N 2 O mole fraction suggest that the total N 2 O flux ( F T ) at 2015 CE was 17.5 ± 1.1 TgN yr −1 , where flux from the natural ( F N ) and anthropogenic ( F A ) sources were ∼60% and 40% of F T , respectively, and the contribution of F A was ∼30% of F T at 1900 CE. Estimated F A and δ 15 N bulk of atmospheric N 2 O suggest that the anthropogenic emissions from continental regions were 12%, 25% and 76% of F A during P1, P2 and P3 phases, respectively.