Measuring and modeling the lifetime of nitrous oxide including its variability

Abstract

The lifetime of nitrous oxide, the third‐most‐important human‐emitted greenhouse gas, is based to date primarily on model studies or scaling to other gases. This work calculates a semiempirical lifetime based on Microwave Limb Sounder satellite measurements of stratospheric profiles of nitrous oxide, ozone, and temperature; laboratory cross‐section data for ozone and molecular oxygen plus kinetics for O(1D); the observed solar spectrum; and a simple radiative transfer model. The result is 116 ± 9 years. The observed monthly‐to‐biennial variations in lifetime and tropical abundance are well matched by four independent chemistry‐transport models driven by reanalysis meteorological fields for the period of observation (2005–2010), but all these models overestimate the lifetime due to lower abundances in the critical loss region near 32 km in the tropics. These models plus a chemistry‐climate model agree on the nitrous oxide feedback factor on its own lifetime of 0.94 ± 0.01, giving N2O perturbations an effective residence time of 109 years. Combining this new empirical lifetime with model estimates of residence time and preindustrial lifetime (123 years) adjusts our best estimates of the human‐natural balance of emissions today and improves the accuracy of projected nitrous oxide increases over this century.

Preindustrial nitrous oxide emissions from the land biosphere estimated by using a global biogeochemistry model

“…Prather et al (2012) provided an estimate of 9.1 ± 1.0 Tg N yr −1 of natural emissions in the preindustrial era using observed preindustrial abundances of 270 ppb and model estimates of lifetime decreases from 142 years in the preindustrial era to 131 ± 10 years in the present day. Later, Prather et al (2015) reevaluated N 2 O lifetime based on Microwave Limb Sounder satellite measurements of the stratosphere, which were consistent with modeled values in the present day. The lifetime in the preindustrial era and the present day was estimated to be 123 and 116 ± 9 years, respectively.…”

“…Based on the IPCC AR5, Davidson and Kanter (2014) indicated that the central estimates of both top-down and bottom-up approaches for preindustrial natural emissions were in agreement at 11 (10-12) Tg N yr −1 , including natural emission from soils at 6.6 (3.3-9.0) Tg N yr −1 (Syakila and Kroeze, 2011). Prather et al (2015) provided an estimate of the preindustrial emissions (total natural emission: 10.5 Tg N yr −1 ) based on the most recent study with a corrected lifetime of 116 ± 9 years. Although these previous estimates intend to provide a baseline of preindustrial N 2 O emission at a global level, information on preindustrial N 2 O emissions at fine resolutions such as biome, sector or country, and regional levels remains unknown but is needed for climate change mitigation.…”

“…Nitrous oxide is also the most longlived reactant, resulting in the destruction of stratospheric ozone (Prather et al, 2015;Ravishankara et al, 2009). The atmospheric concentration of N 2 O has increased from 275 to 329 parts per billion (ppb) since the preindustrial era until 2015 at a rate of approximately 0.26 % per year, as a result of human activities (Davidson, 2009;Forster et al, 2007;NOAA2006A, 2016.…”

“…Numerous studies have reported the sources and estimates of N 2 O emission since the preindustrial era (Davidson and Kanter, 2014;Galloway et al, 2004;Kroeze et al, 1999;Prather et al, 2012Prather et al, , 2015Syakila and Kroeze, 2011). According to the Intergovernmental Panel on Climate Change Guidelines (IPCC, 1997), the global N 2 O emission evaluated by Kroeze et al (1999) is 11 (8-13) Tg N yr −1 (natural soils: 5.6-6.6 Tg N yr −1 ; anthropogenic: 1.4 Tg N yr −1 ), which is consistent with the estimation from global preagricultural N 2 O emissions in soils (6-7 Tg N yr −1 ) (Bouwman et al, 1993).…”

“…Since there are no observational data of N 2 O emission in the preindustrial period, the estimates of natural emission from Prather et al (2012Prather et al ( , 2015 were used to validate the simulation results. In addition, site-level N 2 O emissions from different natural vegetation were used to test model performance in the contemporary period.…”