Table 1.
Reactive N inputs to the biosphere and atmosphere, atmospheric N2O mixing ratios and associated N2O emission factors in 1860 and 2000 (after Crutzen et al. [10]).
| source/process | annual rate/ EF | reference |
|---|---|---|
| 1860 (atmospheric mixing ratio = 270 ppbv) | ||
| [A] total N2O source | 10.2 Tg N2O-N yr−1 | [11] |
| [B] land and coastal zone source | 6.2–7.2 Tg N2O-N yr−1 | [11] |
| [C] input of new reactive N | 141 Tg N yr−1 | [5] |
| [D] N2O emission factor (i.e. [B]/[C]) | 4.4–5.1% | |
| 2000 (atmospheric mixing ratio = 315 ppbv) | ||
| [E] atmospheric increase | 3.9 Tg N2O-N yr−1 | [11] |
| [F] photochemical loss (stratosphere) | 11.9 Tg N2O-N yr−1 | [11] |
| [G] total N2O source (= [E] + [F]) | 15.8 Tg N2O-N yr−1 | |
| [H] decrease in natural source | 0–0.9 Tg N2O-N yr−1 | [12] |
| [I] total anthropogenic source (i.e. [G] − [A] + [H]) | 5.6–6.5 Tg N2O-N yr−1 | |
| [J] non-biological anthropogenic source | 0.7–1.3 Tg N2O-N yr−1 | [11] |
| [K] land/coastal zone biological source (=[I] − [J]) | 4.3–5.8 Tg N2O-N yr−1 | |
| [L] new terrestrial anthropogenic N input | 114 Tg N yr−1 | [5,13] |
| [M] N2O emission factor for new N (i.e. [K]/[L]) | 3.8–5.1% |