DOI: 10.5061/dryad.vmcvdnd6m
title: Data from: Projecting nitrous oxide over the 21<sup>st</sup> century, uncertainty related to stratospheric loss

description: This data set includes the analysis and graphical data in the PNAS
 publication entitled "Projecting nitrous oxide over the 21st century,
 uncertainty related to stratospheric loss". The data is in the form
 of column vectors of various derived products involving N2O, NOy, O3, and
 QBO indices that are plotted in the paper. The abscissa can be year,
 month, or lag time (months). The data is provided in an Excel spreadsheet
 with tabs for each figure. The data is available for open use, and there
 are no ethical or legal considerations related to its use in subsequent
 research. The abstract and significance statement of the publication
 follow. Abstract. Extending the N2O lifetime derived from Microwave Limb
 Sounder satellite observations, we find a mean value of 117 yr and a
 likely decrease of –1.4 ± 0.9 % per decade over the period 2004-2024. This
 trend is consistent with the previously published 2004-2021 value of –2.1
 ± 1.2 % per decade. A more careful analysis of uncertainty now provides a
 more robust likely (one-sigma) range. From analyses of a range of factors
 controlling the N2O lifetime, we find that the decrease in lifetime can be
 explained by recent changes in stratospheric circulation and temperature.
 Projection of the lifetime change to 2100 shows that this effect is
 comparable to differences across the shared socioeconomic pathways used
 for climate projections and cannot be ignored. An updated evaluation of
 the N2O chemical feedbacks shows that this effect produces a relatively
 small shift in atmospheric abundance over the 21st century, but still an
 important shift, –11%, in the global warming potential of N2O. 
 Significance. Projecting atmospheric nitrous oxide (N2O) abundance is
 critical for climate and ozone assessments. Research has focused on
 projecting the changing emissions of N2O from direct anthropogenic
 sources, the dominant cause of the recent growth. Earth system models are
 now projecting natural sources perturbed by climate change. There has been
 little effort to understand how climate and compositional changes may
 change the stratospheric sink of N2O, which balances all these sources and
 also controls the atmospheric abundance. Here, we review recent
 observational and modeling evidence for an increase in the sink caused by
 decreasing N2O lifetime and show that it introduces uncertainties
 comparable to shifts across the different shared socioeconomic pathway
 (SSP) scenarios used in current assessments.
description: # Data from: Projecting nitrous oxide over the 21^st^ century, uncertainty
 related to stratospheric loss Dataset DOI:
 [10.5061/dryad.vmcvdnd6m](https://doi.org/10.5061/dryad.vmcvdnd6m) ##
 Description of the data and file structure **Description of the data and
 file structure** The data here are derived from public sources and are in
 the form of monthly means or 12-month running sums. The data from the
 analysis are provided in a spreadsheet (.xlsx format). ### Files and
 variables #### **Files and variables** **File: 2025PNAS_N2O_Figures.pdf**
 **Description:** Published figures along with captions. The captions give
 a more detailed description of the data being plotted. An alternative to
 Fig. 4, using the earlier N~2~O scenarios (RCPs), is provided. **File:
 2025_N2O_PNAS-datasets.xlsx** **Description:** Monthly data used in this
 analysis and shown in the published figures are given in the
 spreadsheet. This analysis is accepted for publication in PNAS as #
 2025-24123R on 26 Dec 2025. ***Tab: monthly data*** These monthly data are
 averages over the month and are plotted as the middle of the month. Please
 note that blank cells mean that there is NO DATA available for these times
 and the analysis did not use any assumed values for the variables. A.
 month (#1 = Jan 2004) B. year (and month as a fraction of the year) C.
 N~2~O (ppb, mol/mol) D. N~2~O Loss (kg-N/sec) E. NOy Prod (kg-N/sec) F.
 N~2~O Mass (Tg-N) G. days / month H. u wind @ 10 hPa from Singapore sonde
 (m/s) ***Tab: annual mean data*** These annual mean data are calculated as
 the day-weighted average of the monthly means. They are plotted at the
 first of each month, i.e., the 12-month running average of Jan through Dec
 of 2005 is plotted at 1 Jul 2005 (2005.5). All months are treated as being
 of equal length (1/12 of a year) for plotting purposes, but each monthly
 mean is weighted by the days in the month. February monthly data are
 always weighted by 28.25 days to give an accurate annual mean, assuming
 that the year is 365.25 days long (Julian calendar). A. year B. N~2~O
 (ppb, mol/mol) C. N~2~O Loss (Tg-N/yr) D. NOy Prod (Tg-N/yr) E. N~2~O Mass
 (Tg-N) ***Tab: Fig. 1abcd*** A. X-axis (mon) B. Fig1a L-N~2~O (loss in
 Tg-N/yr) C. Fig1b NOy yield (% N/N) D. Fig1c Altitude (km) of L-N~2~O E.
 Fig1c Altitude (km) of P-NOy F. Fig1d Latitude (deg) of L-N~2~O G. Fig1d
 Latitude (deg) of P-NOy Caption: Fig. 1. (a) Monthly annual cycle of N~2~O
 loss rate (TgN/y) calculated from the MLS monthly data for N~2~O, O~3~,
 and T for Jan 2005 through Dec 2024. (b) Annual cycle of NOy yield (% per
 N~2~O lost as N per N). (c) Mean altitude (km, in pressure altitude) of
 the N~2~O loss ('o') and NOy production ('x'). (d)
 Mean latitude (degrees) of the N~2~O loss ('o') and NOy
 production ('x').  ***Tab: Fig. 2abcd*** A. X-axis (yr) B. Fig2a
 N~2~O mass (Tg-N) C. Fig2a linear fit to N~2~O mass D. Fig2b L-N~2~O (loss
 in Tg-N/yr) E. Fig2b linear fit to L-N~2~O F. Fig2c NOy yield (%N;N) G.
 Fig2c linear fit to NOy yield H. Fig2d N~2~O lifetime (yr) I. Fig2d linear
 fit to N~2~O lifetime J. Fig2d linear fit to N~2~O lifetime using only
 years 2004-2021 Caption: Fig. 2. Interannual variability (IAV) of key
 N~2~O quantities. All data here have the annual cycle removed (see Fig. 1)
 by summing or averaging over 1 year with daily weighting for each month
 from Aug 2004 through Dec 2024. Every Feb has 28.25 days. The first point
 covers Aug 2004 through Jul 2005 and is plotted as 1 Feb 2005. The last
 point is the sum over Jan 2024 through Dec 2024 and plotted as 1 Jul 2024.
 (a) N~2~O total atmospheric mass (TgN) derived from NOAA monthly global
 mean surface observations (ref) and a scaling factor of 4.79 TgN/ppb. The
 linear trend line fit (+3.0 %/dec) shows the positive residuals of the fit
 at both ends, indicating the parabolic pattern of the N~2~O growth rate,
 corresponding to a near uniform acceleration of 2.1 % yr^2^. (b) N~2~O
 loss rate (TgN/y) calculated from the MLS monthly data for N~2~O, O~3~,
 and T for Aug 2004 through Dec 2024. The trend line (+4.4 %/dec) shows
 that N~2~O loss is increasing faster than the burden. The IAV is much
 smaller than the annual cycle (Fig. 1a) and correlates with QBO winds
 (Fig. 3a). (c) Yield rate of NO (%) in terms of moles of N produced per
 moles of N lost of N~2~O. (d) Annual mean lifetime of N~2~O (y) derived
 from panels (a) and (b). The solid black trend line (–1.4 %/dec) for the
 extended period is compared with that from previous analysis using data
 through Dec 2021 (dotted line, –2.1 %/dec, Prather et al., 2023). The mean
 lifetime for either period is 117.3 y.  ***Tab: Fig. 3abc*** A. X-axis
 (lag in mon) B. Fig3a Xcorr (cross correlation) of u10 v. L-N~2~O C. Fig3a
 Xcorr of u10 v. P-NOy D. Fig3b Xcorr of P-NOy vs. L-N~2~O E. Fig3c Xcorr
 of L-N~2~O vs. w @ 30hPa F. Fig3c Xcorr of L-N~2~O vs. w @ 20 hPa G. Fig3c
 Xcorr of L-N~2~O vs. w @ 10 hPa H. Fig3c Xcorr of L-N~2~O vs. w @ 7 hPa I.
 Fig3c Xcorr of L-N~2~O vs. w @ 5 hPa Caption: Fig. 3. (a) Cross
 correlation of detrended N~2~O loss ('o') and NOy production
 ('x') against QBO metric (u~10~ = equatorial wind at 10 hPa),
 showing peak correlation with N~2~O-loss of –0.47 at –4 months (vertical
 dotted line, N~2~O lagging QBO). All data have been yearly averaged,
 month-by-month. (b) Cross correlation of NOy production against N~2~O
 loss, showing peak correlation of 0.98 and no significant lag. (c) Cross
 correlation of N~2~O loss against residual vertical velocity w*~QBO~ at
 pressure levels: 30, 20, 10, 7, 5 hPa. ***Tab: Fig. 4*** A. X-axis (years)
 B. projected N~2~O abundance (ppb) assuming constant growth of +3 %/dec,
 and fixed lifetime C. projected N~2~O abundance assuming lifetime decrease
 of -2.1 %/dec D. projected N~2~O abundance assuming lifetime decrease of
 -1.4 %/dec E. projected N~2~O abundance assuming lifetime decrease of -1.4
 %/dec and including chemical feedback F. (intentionally left blank) G.
 second X-axis (decadal years) H. SSP1-2.6 decadal projections for N~2~O
 (ppb) I.  SSP2-4.5 ibid J.  SSP3-7.0 ibid K. SSP4-6.0 ibid L. SSP5-8.5
 ibid Caption: Figure 4. Observed (2000-2024) and projected (2025-2100)
 N~2~O annual mean tropospheric abundance (gray line) assuming the observed
 2005-2024 +3.0 %/decade growth rate continues to 2100. N~2~O emissions
 (2025-2100) are calculated from this projection assuming a fixed lifetime
 of 120 yr. Using these emissions, the N~2~O abundance is projected (black
 lines) using three different lifetime assumptions: (solid line) lifetime
 decreases at –1.4 % per decade; (thin dotted line) same lifetime trend
 plus a chemical feedback factor that reduces the lifetime with increasing
 burden (i.e., dln(N~2~O lifetime) / dln(N~2~O burden) = –0.065; Prather
 and Hsu, 2010); and (dashed line) the lifetime decreases at –2.1 % per
 decade as found from the earlier period 2004-2021 (Prather et al., 2023).
 The reduction in 2100 N~2~O abundance for these three cases are –4.3,
 –4.5, and –6.5 %, respectively. A range of SSP emissions scenario
 projections (Shared Socio-economic Pathways: SSP1-2.6, SSP2-4.5, SSP5-8.5,
 SSP4-6.0, SSP3-7.0, in ascending order) calculated by Meinshausen et al.
 (2020) for the IPCC assessments are shown for perspective. ##
 Code/software **Code/software** The Figure/ data sets are given in a .xlsx
 file with separate page tabs for each Figure. ## Access information
 **Access information** Data used in this analysis was collected from the
 following sources: ***N~2~O surface abundance from NOAA***: G.S. Dutton
 *et al.*, Combined Atmospheric Nitrous Oxide Dry Air Mole Fractions from
 the NOAA GML Halocarbons Sampling Network, 1977-2024, Version: 2024-02-21,
 doi: 10.15138/GMZ7-2Q16, creation date: 14 Mar 2025 (Xin Lan),
 [https://gml.noaa.gov/webdata/ccgg/trends/N~2~O/N~2~O_mm_gl.txt](https://gml.noaa.gov/webdata/ccgg/trends/N~2~O/N~2~O_mm_gl.txt), (accessed 30 March 2025) ***MLS O~3~profiles from JPL:*** M. Schwartz, L. Froidevaux, N. Livesey, W. Read, R. Fuller, MLS/Aura Level 3 Monthly Binned Ozone (O3) Mixing Ratio on Assorted Grids V005, Greenbelt, MD, USA, Goddard Earth Sciences Data and Information Services Center (GES DISC), doi: 10.5067/Aura/MLS/DATA/3546 (accessed 30 March 2025). ***MLS temperature profiles from JPL:*** M. Schwartz, N. Livesey, W. Read, R. Fuller, MLS/Aura Level 3 Monthly Binned Temperature on Assorted Grids V005, Greenbelt, MD, USA, Goddard Earth Sciences Data and Information Services Center (GES DISC), doi: 10.5067/Aura/MLS/DATA/3550 (accessed 30 March 2025). ***MLS N~2~O profiles from JPL:*** A. Lambert, N. Livesey, W. Read, R. Fuller, MLS/Aura Level 3 Monthly Binned Nitrous Oxide (N~2~O) Mixing Ratio on Assorted Grids V005, Greenbelt, MD, USA, Goddard Earth Sciences Data and Information Services Center (GES DISC), doi: 10.5067/Aura/MLS/DATA/3545 (accessed 30 March 2025). ***Singapore u winds at 10 hPa:*** T. Kerzenmacher, P. Braesicke, QBO: monthly zonal stratospheric winds from tropical radiosonde data (mainly Singapore), [https://zenodo.org/records/14037052](https://zenodo.org/records/14037052), (accessed 20 Jum 2025) ***MERRA-2 w*** **profiles from NASA:*** P.A. Newman, L. Coy, S. Pawson, The Quasi-biennial Oscillation (QBO), Vertical residual velocity (mm/s) monthly means from MERRA-2 (5S-5N), 1980/01-2025/05, [https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo.html](https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo.html), and [https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/QBO_MERRA2-Wvals_05S-05N_GSFC.txt](https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/QBO_MERRA2-Wvals_05S-05N_GSFC.txt) (accessed 23 Jun 2025)