1. Tiger Team project : Processes contributing to model differences in North American background ozone estimates NASA AQAST Meeting University of Wisconsin-Madison June 14, 2012 AQAST PIs: Arlene Fiore (Columbia/LDEO) and Daniel Jacob (Harvard) Co-I: Meiyun Lin (Princeton/GFDL) Project personnel: Jacob Oberman (U Wisconsin) Lin Zhang (Harvard) AQ management contacts: Joe Pinto (EPA/NCEA) Pat Dolwick (EPA/OAR/OAQPS)

2. Objective: Improved error estimates of simulated North American background O 3 (NAB) Problem: Poorly quantified errors in NAB distributions complicate NAAQS- setting and interpreting SIP attainment simulations To date, EPA NAB estimates have been provided by one model. Approach: 1)Compare GFDL AM3 and GEOS-Chem NAB (regional, seasonal, daily) 2)Process-oriented analysis of factors contributing to model differences YEAR 2006GEOS-ChemGFDL AM3 Resolution ½°x⅔° (and 2°x2.5°) ~2°x2° Meteorology Offline (GEOS-5)Coupled, nudged to NCEP U and V Strat. O 3 & STE Parameterized (Linoz)Full strat. chem & dynamics Isoprene nitrate chemistry 18% yield w/ zero NO x recycling 8% yield w/ 40% NO x recycling (obs based; Horowitz et al, 2007) Lightning NO x tied to model convective clouds, scaled to obs. flash climat; higher NO x at N. mid-lat tied to model convective clouds Emissions NEI 2005 + 2006 fires (emitted at surface) ACCMIP historical + RCP4.5 (2005, 2010); vert. dist. climatological fires ALL DIFFERENT!

3. Seasonal mean North American background in 2006 (estimated by simulations with N. American anth. emissions set to zero) AM3 (~2°x2°)GEOS-Chem (½°x⅔°) North American background (MDA8) O 3 in model surface layer AM3: More O 3 -strat + PBL-FT exchange? GC: More lightning NO x (~10x over SWUS column) + spatial differences Summer (JJA) Spring (MAM) J. Oberman Different contributions from summertime Canadian wildfires? (use of 2006 in GC vs climatology in AM3) ppb

4. Space-based constraints on mid-trop O 3 ? Comparison with OMI & TES “500 hPa” in spring  Models bracket retrievals  Qualitative constraints where the retrievals agree in sign L. Zhang Bias vs. N mid- latitude sondes subtracted from retrievals Masked out where products disagree by > 10 ppb

5. Large differences in day-to-day and seasonal variability of N. American background: Eastern USA, Mar-Aug 2006 GEOS-Chem ( ½°x⅔° ) AM3 (~2°x2°) OBS. AM3 NAB declines in Jul/Aug (when total O 3 bias is worst) GC NAB varies less than AM3 (total O 3 has similar variability) GC NAB declines into summer AM3 NAB too high in summer: Excessive fire influence? Does model horizontal resolution matter? Both models too high in summer Similar correlations with obs GC captures mean AM3 +11 ppb bias: isop. chem.? Georgia Station, GA: 84W, 33N, 270m Voyageurs NP, MN: 93W, 48N, 429m Mean(σ) Total model O 3 Model NAB O 3

6. Horizontal resolution not a major source of difference in model NAB estimates Between OBS GC Higher resolution broadens distribution + shifts closer to observed mean (lower) GC 2°x2.5° GC ½°x⅔° GC High-res shows slight shift towards higher NAB (vertical eddies [Wang et al., JGR, 2004]) GC NAB 2°x2.5° GC NAB ½°x⅔° AM3 ~2°x2° AM3 NAB ~2°x2° AM3 represents distribution shape but biased high  Much larger differences between AM3 and GC distributions (both total and NAB O 3 ) than between the 2 GC resolutions SPRING (MAM) CASTNet sites above1.5 km GC ½°x⅔° similar to GC 2°x2.5° LARGEST DIFFERENCES OCCUR IN SUMMER at CASTNET SITES < 1.5 km (CONUS except CA)

7. Large differences in day-to-day and seasonal variability of N. American background: Western USA, Mar-Aug 2006 Gothic, CO: 107W, 39N, 2.9km Grand Canyon NP, AZ: 112W, 36N, 2.1km Mean(σ) GEOS-Chem ( ½°x⅔° ) AM3 (~2°x2°) OBS. Total model O 3 Model NAB O 3 Models bracket Obs. AM3 larger σ than GC (matches obs) Mean NAB is similar GC NAB ~2x smaller σ than AM3 AM3 NAB > GC NAB in MAM (strat. O 3 ?); reverses in JJA (lightning)  Fig 3-58 of O 3 Integrated Science Assessment

8. How much does N. American background vary year-to-year? Western CO experiences largest year-to-year variability: What drives this? NORTH AMERICAN BACKGROUND IN AM3 (ZERO N. Amer. emissions 1981-2007) MEAN OVER 27 YEARS STANDARD DEVIATION ppb

9. Stratospheric O 3 : key driver of daily (+ inter-annual) variability, particularly late spring – e.g. 1999 shown here Langford et al., 2009 AM3 O 3 -strat OBS  Examine observational constraints on strat. influence (M. Lin) M. Lin r 2 =0.45 (vs. obs)r 2 =0.50 (vs. obs) r 2 =0.44 (vs. obs)r 2 =0.31 (vs. obs)

10. Improved error estimates of simulated North American background O 3 (NAB) that inform EPA analyses AQ management outcomes: Improved NAB error estimates to support: (1) ongoing review of ozone NAAQS (EPA ISA for O 3 ), (2) SIP simulations focused on attaining NAAQS, (3) development of criteria for identifying exceptional events Deliverables: 1) Report to EPA on confidence and errors in NAB estimates & key factors leading to model differences (peer-reviewed publication) 2) Guidance for future efforts to deliver estimates of sources contributing to U.S. surface O 3 What next?  satellite constraints: how quantitative?  multi-model effort (more robust; error characterization)? -- focus on specific components of NAB tied to multi-platform observations -- choose a common study period (2008? 2010-2011)? -- leverage AQAST IP + other TT projects where possible