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Tiger Team project :

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)

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Tiger Team project :

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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 O3 (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: • Compare GFDL AM3 and GEOS-Chem NAB (regional, seasonal, daily) • Process-oriented analysis of factors contributing to model differences ALL DIFFERENT!

  3. Seasonal mean North American background in 2006 (estimated by simulations with N. American anth. emissions set to zero) North American background (MDA8) O3 in model surface layer AM3 (~2°x2°) GEOS-Chem (½°x⅔°) AM3: More O3-strat + PBL-FT exchange? Spring (MAM) GC: More lightning NOx (~10x over SWUScolumn) + spatial differences Summer (JJA) ppb J. Oberman Different contributions from summertime Canadian wildfires? (use of 2006 in GC vs climatology in AM3)

  4. Space-based constraints on mid-trop O3? Comparison with OMI & TES “500 hPa” in spring Bias vs. N mid-latitude 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 GEOS-Chem ( ½°x⅔° ) AM3 (~2°x2°) OBS. Mean(σ) Total model O3 Model NAB O3 AM3 NAB too high in summer: Excessive fire influence? GC NAB declines into summer Georgia Station, GA: 84W, 33N, 270m 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 O3 bias is worst) GC NAB varies less than AM3 (total O3 has similar variability) Does model horizontal resolution matter?

  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 Higher resolution broadens distribution + shifts closer to observed mean (lower) GC NAB 2°x2.5° GC NAB ½°x⅔° GC High-res shows slight shift towards higher NAB (vertical eddies [Wang et al., JGR, 2004]) AM3 NAB ~2°x2° GC 2°x2.5° OBS GC ½°x⅔° AM3 ~2°x2° AM3 represents distribution shape but biased high SPRING (MAM) CASTNet sites above1.5 km GC ½°x⅔° similar to GC 2°x2.5° • Much larger differences between AM3 and GC distributions (both total and NAB O3) than between the 2 GC resolutions

  7. Large differences in day-to-day and seasonal variability of N. American background: Western USA, Mar-Aug 2006 GEOS-Chem ( ½°x⅔° ) AM3 (~2°x2°) OBS. Gothic, CO: 107W, 39N, 2.9km Mean(σ) Total model O3 Model NAB O3 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. O3?); reverses in JJA (lightning) Fig 3-58 of O3 Integrated Science Assessment Grand Canyon NP, AZ: 112W, 36N, 2.1km

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

  9. Stratospheric O3: key driver of daily (+ inter-annual) variability, particularly late spring – e.g. 1999 shown here r2=0.44 (vs. obs) r2=0.31 (vs. obs) OBS AM3 O3-strat r2=0.45 (vs. obs) r2=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 O3 (NAB) that inform EPA analyses • AQ management outcomes: • Improved NAB error estimates to support: • ongoing review of ozone NAAQS (EPA ISA for O3), • SIP simulations focused on attaining NAAQS, • development of criteria for identifying exceptional events • Deliverables: • Report to EPA on confidence and errors in NAB estimates & key factors leading to model differences (peer-reviewed publication) • Guidance for future efforts to deliver estimates of sources contributing to U.S. surface O3 • 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

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