Simulation of N2O with GEOS-Chem and its adjoint: evaluation of observational constraints 

Kelley Wells, Dylan Millet, Nicolas Bousserez, Daven Henze, Tim Griffis, Sree Chaliyakunnel, Yurong Luan + coauthors

IGC7, 6 May 2015

N2O~325 ppb

Lifetime: 124-130 years

+ hν(90 %)

+ O(1D)(10 %)

stratosphere

Growth rate: ~0.8 ppb/year

Soils

EDGAR

Industry

EDGAR

Biomass burning

GFEDv3

Ocean

Jin and Gruber (2003)

2.4 Tg N 0.6 Tg N

7.7 Tg N

3.5 Tg N

N2O observing system: April 2010-April 2012

1) How well do different observations constrain emissions and sink of N2O, and at what time and space resolution?2) Where are additional measurements needed to get better observational constraints on N2O emissions?4D-Var inversion, monthly scaling factors:• Emissions, 4° x 5° • Stratospheric loss frequencies,

8 latitude bands

Cruising altitude

Vertical profiles

CARIBIC

HIPPO

Surface flask and hourly obs

Dlugokencky, Prinn, Weiss, O’Doherty, Krummel, Dutton, Elkins, Steele, Langenfelds, Worthy, Nichol, Griffis et al.

Kort, Wofsy et al.

Brenninkmeijer, Umezara et al.

Observing system simulation experiments test ability of inversion to recover known N2O emissions

Pseudo obs

Perturbed initial state

SF = 1 “true” state

Surface and HIPPO recover “true” zonal emissions

CARIBIC provides weaker constraint

Uniform bias is well-resolved using surface and HIPPO,

but a seasonally or spatially-varying bias is more

challenging

Error reduction from stochastic approx. of inverse Hessian:

A posteriori error indicates where N2O observations provide spatially-resolved emission constraints

postyT

a SxJ SH)HS())(( -11112

Lack of tropical constraints from ALL measurements

Constraints near and upwind of hourly obs

Constraints near and upwind of flight tracks

Inversion AKs indicate where emissions can be independently resolved from emissions elsewhere

Rows of AK for emissions in specific locations using

surface pseudo observations

AK smearing = tropical emissions conflated with extratropical emissions

Hourly obs =

well-resolved

local emissions

Weekly obs = somewhat weaker

local constraint

“Unconstrained” N2O distribution helps identify priority regions for new N2O measurements

Unconstrained N2O = E*(1 – x),

x = error reduction achieved with surface

pseudo obs

August – September 2010

Additional aircraft obs could help constrain tropical emissions

Observing system simulation experiments test ability of inversion to recover known stratospheric sinkSurface HIPPO CARIBIC

Strat loss frequency bias won’t affect inferred source

at timescale of inversion, but STE bias likely will

Perturb kSTEPerturb kchem

Recovery of bias in summer months, no recovery in joint inversion

Seasonal biases are more difficult to resolve, but some seasonal constraints are achieved near and upwind of obs

201005

1.5× bias applied Mar – Aug, 0.5× bias applied Sep – Feb

N2O observing network: April 2010 – April 2012

Surface flask and hourly obs

CARIBIC aircraft obs

HIPPO aircraft obs

NOAA CCGG (Dlugokencky et al)NOAA CATS (Elkins, Dutton et al.)CSIRO (Krummel et al.)AGAGE (Prinn, Weiss, O’Doherty et al.)NIWA (Nichol et al.)UMN KCMP tall tower (Griffis et al.)

HIPPO III: 24 March – 16 April 2010HIPPO IV: 14 June – 11 July 2010

HIPPO V: 9 August – 9 September 2010

(Brenninkmeijer, Ukemara, Schuck et al.)

(Kort, Wofsy et al.)

Cruising altitude

Vertical profiles

CARIBIC aircraft obs