Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion

Abstract

Abstract. N 2 O surface fluxes were estimated for 1999 to 2009 using a time-dependent Bayesian inversion technique. Observations were drawn from 5 different networks, incorporating 59 surface sites and a number of ship-based measurement series. To avoid biases in the inverted fluxes, the data were adjusted to a common scale and scale offsets were included in the optimization problem. The fluxes were calculated at the same resolution as the transport model (3.75 • longitude × 2.5 • latitude) and at monthly time resolution. Over the 11-year period, the global total N 2 O source varied from 17.5 to 20.1 Tg a −1 N. Tropical and subtropical land regions were found to consistently have the highest N 2 O emissions, in particular in South Asia (20 ± 3 % of global total), South America (13 ± 4 %) and Africa (19 ± 3 %), while emissions from temperate regions were smaller: Europe (6 ± 1 %) and North America (7 ± 2 %). A significant multi-annual trend in N 2 O emissions (0.045 Tg a −2 N) from South Asia was found and confirms inventory estimates of this trend. Considerable interannual variability in the global N 2 O source was observed (0.8 Tg a −1 N, 1 standard deviation, SD) and was largely driven by variability in tropical and subtropical soil fluxes, in particular in South America (0.3 Tg a −1 N, 1 SD) and Africa (0.3 Tg a −1 N, 1 SD). Notable variability was also found for N 2 O fluxes in the tropical and southern oceans (0.15 and 0.2 Tg a −1 N, 1 SD, respectively). Interannual variability in the N 2 O source shows some correlation with the El Niño-Southern Oscillation (ENSO), where El Niño conditions are associated with lower N 2 O fluxes from soils and from the ocean and vice versa for La Niña conditions.

Tracking nitrous oxide emission processes at a suburban site with semicontinuous, in situ measurements of isotopic composition

“…The mean mole fraction (328.9 ± 3.6 ppb) is above the mean Northern Hemisphere (NH) background value of 327.6 ± 0.2 ppb for the same time period (Advanced Global Atmospheric Gases Experiment network data [ Prinn et al , , ; Thompson et al , ]), as Dübendorf is a suburban site. The observed trend for all data of 0.73 ± 0.3 ppb yr −1 in N 2 O mole fraction is in good agreement with the result of 0.72 ppb yr −1 for Hateruma Island, Japan [ Toyoda et al , ], as well as the Northern Hemisphere mean trend for the last 5 years of 0.94 ± 0.02 ppb yr −1 [ Prinn et al , , ; Thompson et al , ]. The isotopic trends are much larger than observed previously [ Toyoda et al , ], which may be due to seasonality and/or interannual variability in isotopic composition and magnitude of the regional source.…”

Correcting oceanic O2/Ar‐net community production estimates for vertical mixing using N2O observations

“…The oceans are believed to contribute approximately one third of the natural N 2 O flux to the atmosphere [ Hirsch et al ., ; Seitzinger et al ., ]. Oceanic sources of N 2 O are only poorly constrained based on bottom up estimates, with a range of 1.2–6.8 Tg N yr −1 [ Nevison et al ., , ] but generally fall in a narrower 4–6 Tg N yr −1 range in recent top down atmospheric inversions [ Saikawa et al ., ; Thompson et al ., ].…”

Comparisons of continuous atmospheric CH<sub>4</sub>, CO<sub>2</sub> and N<sub>2</sub>O measurements – results from a travelling instrument campaign at Mace Head

“…This may reinforce the possibility of a current smallscale difference between the WMO X2006a scale and the SIO-1998 scale, which could be of the order of −0.1 to −0.4 nmol mol −1 (SIO-1998 -WMO X2006a). Note, however, that Thompson et al (2014) …”