1. Simulation of N 2 O 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 N 2 O ~325 ppb Lifetime: 124-130 years + hν (90 %) + O( 1 D) (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

2. N 2 O observing system: April 2010-April 2012 1) How well do different observations constrain emissions and sink of N 2 O, and at what time and space resolution? 2) Where are additional measurements needed to get better observational constraints on N 2 O 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.

3. Observing system simulation experiments test ability of inversion to recover known N 2 O 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

4. Error reduction from stochastic approx. of inverse Hessian: A posteriori error indicates where N 2 O observations provide spatially-resolved emission constraints Lack of tropical constraints from ALL measurements Constraints near and upwind of hourly obs Constraints near and upwind of flight tracks

5. 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

6. “Unconstrained” N 2 O distribution helps identify priority regions for new N 2 O measurements Unconstrained N 2 O = E*(1 – x), x = error reduction achieved with surface pseudo obs August – September 2010 Additional aircraft obs could help constrain tropical emissions

8. Observing system simulation experiments test ability of inversion to recover known stratospheric sink Surface HIPPO CARIBIC Strat loss frequency bias won’t affect inferred source at timescale of inversion, but STE bias likely will Perturb k STE Perturb k chem Recovery of bias in summer months, no recovery in joint inversion

9. 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

10. N 2 O 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 2010 HIPPO 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