Tiger Team project:

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

YEAR 2006 GEOS-Chem GFDL AM3
Resolution ½x? (and 2x2.5) 2x2
Meteorology Offline (GEOS-5) Coupled, nudged to NCEP U and V
Strat. O3 STE Parameterized (Linoz) Full strat. chem dynamics
Isoprene nitrate chemistry 18 yield w/ zero NOx recycling 8 yield w/ 40 NOx recycling (obs based Horowitz et al, 2007)
Lightning NOx tied to model convective clouds, scaled to obs. flash climat higher NOx 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)
North American background (MDA8) O3 in model
surface layer
AM3 (2x2)
GEOS-Chem (½x?)
AM3 More O3-strat PBL-FT exchange?
Spring (MAM)
GC More lightning NOx (10x over SWUS column)
spatial differences
Summer (JJA)
ppb
J. Oberman
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 gt 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 ( ½x? ) AM3 (2x2) OBS.
Mean(s)
Total model O3 Model NAB O3
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 lt 1.5 km (CONUS except CA)
OBS

• 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 ( ½x? ) AM3 (2x2) OBS.
Gothic, CO 107W, 39N, 2.9km
Mean(s)
Total model O3 Model NAB O3
Models bracket Obs. AM3 larger s than
GC (matches obs) Mean NAB is similar GC NAB 2x
smaller s than AM3 AM3 NAB gt 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
ppb
ppb
9
Stratospheric O3 key driver of daily (
inter-annual) variability, particularly late
spring e.g. 1999 shown here
r20.44 (vs. obs)
r20.31 (vs. obs)
OBS
AM3 O3-strat
r20.45 (vs. obs)
r20.50 (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