Tiger Team project: Processes contributing to model differences in North American background ozone estimates

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1 Tiger Team project: Processes contributing to model differences in North American background ozone estimates 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) NASA AQAST Meeting University of Wisconsin-Madison June 14, 2012

2 Objective: Improved error estimates of simulated North American background O 3 (NAB) Problem: Poorly quantified errors in NAB distributions complicate NAAQSsetting 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 2006 GEOS-Chem GFDL 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 Isoprene nitrate chemistry Lightning NO x Emissions Parameterized (Linoz) 18% yield w/ zero NO x recycling ALL DIFFERENT! tied to model convective clouds, scaled to obs. flash climat; higher NO x at N. mid-lat NEI fires (emitted at surface) Full strat. chem & dynamics 8% yield w/ 40% NO x recycling (obs based; Horowitz et al, 2007) tied to model convective clouds ACCMIP historical + RCP4.5 (2005, 2010); vert. dist. climatological fires

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

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

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

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

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 Mean(σ) GEOS-Chem ( ½ x⅔ ) AM3 (~2 x2 ) OBS. Total model O 3 Model NAB O 3 Models bracket Obs. Fig 3-58 of O 3 Integrated Science Assessment Grand Canyon NP, AZ: 112W, 36N, 2.1km 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)

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

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

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? )? -- leverage AQAST IP + other TT projects where possible