Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit https://espo.nasa.gov for information about our current projects.


How Atmospheric Chemistry and Transport Drive Surface Variability of N2O and...

Ruiz, D., M. Prather, S. Strahan, R. L. Thompson, L. Froidevaux, and S. Steenrod (2021), How Atmospheric Chemistry and Transport Drive Surface Variability of N2O and CFC-11, J. Geophys. Res., 126, org/10.1029/2020JD033979.

Nitrous oxide (N2O) is a long-lived greenhouse gas that affects atmospheric chemistry and climate. In this work, we use satellite measurements of N2O, ozone (O3), and temperature from the Aura Microwave Limb Sounder (MLS) instrument to calculate stratospheric loss of N2O, and thus its atmospheric lifetime. Using three chemistry transport models simulating the Aura period 2005–2017, we verify the stratospheric sink using MLS data and follow that loss signal down to the surface and compare with surface observations. Stratospheric loss has a strong seasonal cycle and is further modulated by the Quasi-Biennial Oscillation (QBO); these cycles are seen equally in both observations and the models. When filtered for interannual variability, the modeled surface signal is QBO-caused, and it reproduces the observed pattern, highlighting the potential role of the QBO in tropospheric chemistry and composition, as well as in model evaluation. The observed annual surface signal in the northern hemisphere matches well with the models run without emissions, indicating the annual cycle is driven mostly by stratospheretroposphere exchange (STE) flux of N2O-depleted air and not surface N2O emissions. In the southern hemisphere (SH), all three models disagree and thus provide no guidance, except for indicating that modeling annual STE in the SH remains a major model uncertainty. Parallel model simulations of CFCl3, which has greater stratospheric loss that N2O and possibly surreptitious emissions, show that its interannual variations parallel those of N2O, and thus the observed N2O variability can identify the stratospheric component of the observed CFCl3 variability. Plain Language Summary Nitrous oxide (N2O) is a long-lived greenhouse gas that drives climate change and ozone depletion, posing a threat to society's health and well-being. The abundance of N2O at Earth's surface, where we can measure it most precisely, fluctuates over seasons and years due to increasing human emissions, variable natural emissions, varying stratospheric destruction, and the movement of air throughout the atmosphere. Scientists use these fluctuations to separate natural from human emissions and quantify what humans can do to reduce the growth in N2O. In this work, we model the physical side of atmospheric N2O that drives fluctuations through chemistry and atmospheric transport. Our model simulations match most of the observed seasonal and multi-year fluctuations seen in satellite and surface observations, indicating that N2O loss is causing the dominating signal, not emissions. Unfortunately, in the southern hemisphere, the annual cycle of the models is in disagreement and cannot help us interpret the observed fluctuations. In addition to helping understand the human role in N2O increases, we find that the N2O observations provide a valuable test of models and guidance to improve them.

PDF of Publication: 
Download from publisher's website.
Research Program: 
Atmospheric Composition
Tropospheric Composition Program (TCP)
Funding Sources: 
NNX13AL12G 80NSSC20K1237 NNX15AE35G)