Interannual and seasonal variability in atmospheric N₂O

Abstract

[1] The increase in atmospheric N 2 O observed over the last century reflects large-scale human perturbations to the global nitrogen cycle. High-precision measurements of atmospheric N 2 O over the last decade reveal subtle signals of interannual variability (IAV) superimposed upon the more prominent growth trend. Anthropogenic sources drive the underlying growth in N 2 O, but are probably too monotonic to explain most of the observed IAV. The causes of both seasonal and interannual variability in atmospheric N 2 O are explored on the basis of comparisons of a 1993-2004 atmospheric transport simulation to observations of N 2 O at five stations of the Advanced Global Atmospheric Gases Experiment (AGAGE). The complementary tracers chlorofluorocarbons (CFCs) 11 and 12 and SF 6 also are examined. The model simulation does not include a stratospheric sink and thus isolates the effects of surface sources and tropospheric transport. Both model and observations yield correlations in seasonal and interannual variability among species, but only in a few cases are model and observed variability correlated to each other. The results suggest that tropospheric transport contributes substantially to observed variability, especially at Samoa station. However, some features of observed variability are not explained by the model simulation and appear more consistent with a stratospheric influence. At Mace Head, Ireland, N 2 O and CFC growth rate anomalies are weakly correlated to IAV in polar winter lower stratospheric temperature, a proxy for the strength of the mean meridional stratospheric circulation. Seasonal and interannual variability in the natural sources of N 2 O may also contribute to observed variability in atmospheric N 2 O.

Comparison of nitrous oxide (N<sub>2</sub>O) analyzers for high-precision measurements of atmospheric mole fractions

“…The amplitude of the seasonal cycle is smaller in the Southern than in the Northern Hemisphere, with a value of approximately 0.4 ppb at Cape Grim, Tasmania, compared with 0.89 ppb at Mace Head, Ireland (Nevison et al, 2007).…”

Nitrous oxide emissions 1999 to 2009 from a global atmospheric inversion

“…Superimposed on the long-term trend in atmospheric N 2 O, is considerable interannual variability in the growth rate. To date, there have been only a few studies that have tried to understand the mechanisms driving this variability (Nevison et al, 2007(Nevison et al, , 2011; Thompson et al, 2013). On the one hand, the growth rate is influenced by changes in nonemission related variables, such as atmospheric transport, especially stratosphere-to-troposphere transport, which carries N 2 O-depleted air from the stratosphere into the troposphere and has a significant influence on the observed N 2 O seasonal cycle and also contributes to interannual variability (Nevison et al, 2011).…”

“…During El Niño, warm water in the western Pacific migrates eastward and reduces upwelling in the eastern Pacific off the coast of South America, while during La Niña the process is reversed and there is an increase in upwelling (McPhaden et al, 2006). Changes in upwelling affect air-sea N 2 O fluxes through physical and biological processes: physically, by changing the supply of N 2 O-rich water from below the euphotic zone to the surface and thereby the partial pressure of N 2 O in the surface water, and biologically, by changing the supply of nutrients to the surface layer and thus primary production and the production of N 2 O within the surface layer (Nevison et al, 2007). These processes are parameterized in the biogeochemistry model PISCES, used for the prior ocean N 2 O flux in the inversion (Dutreuil et al, 2009).…”

“…In contrast, there was little variability in the global total sink, which varied from 11.8 to 12.6 Tg a −1 N ( Table 8) In addition to variations in the N 2 O source, the tropospheric mole fraction is influenced by variations in stratosphere-to-troposphere exchange (STE) as there is a strong gradient in N 2 O mole fraction across the tropopause, and thus changes in the net air mass exchange between the stratosphere troposphere impact the tropospheric mole fraction (Nevison et al, 2007(Nevison et al, , 2011. Therefore, one important question that arises is, how sensitive are the inversion results to errors in the modelled STE?…”

Atmospheric constraints on 2004 emissions of methane and nitrous oxide in North America from atmospheric measurements and a receptor-oriented modeling framework

“…Many global-scale studies have investigated emissions of methane and nitrous oxide (Prinn et al 1990;Chen and Prinn 2006;Hirsch et al 2006;Houweling et al 2006;Bergamaschi et al 2007;Nevison et al 2007;Huang et al 2008). These studies help immensely to improve understanding of emissions at large spatial and temporal scales (continental and annual).…”