1. Improved understanding of global tropospheric ozone integrating recent model developments Lu Hu (luhu@seas.harvard.edu) With Daniel Jacob, Xiong Liu, Patrick Kim, Katie Travis, Lin Zhang Acknowledgement: Johan Schmidt, Ploy Achakulwisut, Lu L. Shen, Bob Yantosca, Melissa Sulprizio, NASA/GMAO

2. 1-yr benchmarks from Bob Yantosca and Melissa Sulprizio Updated isoprene scheme (OH +8.4%) [Mao et al. 2013] Including Br chemistry (OH - 4.2%) [Parrella et al. 2012] Updated lightning NOx (OH +3.2%) [Murray et al. 2012] Evolution of GEOS-Chem, reflecting the advancement of knowledge Introduced GEOS-FP OH: -4.2 % P(Ox): -10%

3. Introducing GEOS-FP reduces free tropospheric O 3 by 0-10 ppbv GEOS-Chem with GEOSFP– with GEOS5 GEOS-FP meteorological fields (since June 2012): Higher temporal and horizontal resolution Weaker convection Lower temperature  lower global isoprene emission (by 20%) July mean O 3 at 500 hPa:

4. Objective: Evaluate GEOS-Chem with the observations for global tropospheric ozone, and diagnose model weaknesses, using – Ozonesondes (vertical gradient) – OMI satellite data (global distribution) Question : Do recent updates improve our ability to model tropospheric ozone?

5. GEOS-FP generally improves simulated vertical distribution of ozone compared to sonde data for 2012/2013 (annual mean) Ozonesonde GEOS-FP GEOS-5 Ozonesonde data from WOUDC and NOAA/GMD

6. Each point represents monthly mean O 3 at 500 hPa for a specific site GEOS-FP O 3 Also a remarkable job in capturing global tropospheric O 3 variability Mean bias ± StdDev

7. Comparison to bias-corrected OMI satellite data at 400-700 hPa for 2012/2013 [ppbv] OMI ozone data quality is not significantly degraded from 2008 (not shown). OMI O 3 data was corrected for biases (3.6 ppbv) relative to in situ ozonesonde data following the method by Zhang et al. (2010) OMI ozone data from X. Liu

8. Improved ability to model tropospheric ozone compared to early versions Zhang et al., 2010: v8-01-04, 4x5, GEOS-4, 2006, ‘old ’ isoprene chemistry, no Br Hu et al., [in prep]: v9-02, 2x2.5, GEOS-FP, 2012/2013

9. Global comparison to OMI satellite data Mean bias ± StdDev Each point represents seasonal mean O 3 at 400-700hPa for a model grid (2x2.5) Bias-corrected OMI ozone [ppbv] Bias at northern mid-latitude in winter partly due to satellite error

10. Improved ozone simulation is a result of advancing scientific knowledge of atmospheric processes controlling tropospheric ozone GEOS-4 GEOS-5 GEOS-FP Besides meteorological fields, P(Ox) is mostly sensitive to lightning NO x emission and isoprene chemistry

11. Impact of isoprene chemistry on O 3 extends to free troposphere ‘old’ isoprene chemistry: Dry deposition is the only loss pathway for isoprene nitrate Turning off ISOPOOH+OH  IEPOX Turning off isomerisation and self-reaction pathways of ISOPO2 Ozonesonde Base ‘old’ isoprene chemistry Ozone (ppbv)

12. Impact of isoprene chemistry on O 3 extends to free troposphere ‘old’ isoprene chemistry: Dry deposition is the only loss pathway for isoprene nitrate Turning off ISOPOOH+OH  IEPOX Turning off isomerisation and self-reaction pathways of ISOPO2 Ozonesonde Base ‘old’ isoprene chemistry Ozone (ppbv) K. Travis Ozone (ppbv)

13. Conclusions Recent model developments improve GEOS-Chem tropospheric ozone simulations, reflecting integrated improvements in lightning NO x source, isoprene chemistry, Br chemistry, and improved meteorological inputs. Tropospheric ozone simulation is mostly sensitive to model treatments in isoprene chemistry and lightning NO x emissions, and selection of meteorological inputs. Standard GEOS-Chem underestimates free tropospheric O 3 in the northern high latitudes. Standard GEOS-Chem still overestimates O 3 in the Southeast U.S., but this is likely caused by an overestimated US NEI NO x emission (K. Travis).

14. Thanks!

15. Extra

16. 40% reduction in Wet deposition of Ox Wet deposition: a minor term in O 3 budget, but could be important for modeling other species

17. Column total of convective mass flux Isoprene emission

18. Upper troposphere Ozonesonde GEOS-5 GEOS-4

20. Green numbers show the max and min biases relative to sondes Summer high biases in in west Pacific/Indonesia (also seen in 2008) due to OMI row anomaly, noise increase (Xiong Liu) Large biases in Spring and Winter over northern high latitudes; also occur for data before 2009 (not shown) Validating OMI measurements against ozonesondes (2011-2013)

21. High biases in >45N for Spring and Winter OMI O 3 is generally biased high 400-700 hPa: OMI vs sonde (OMI AK) Comparison for 2008 is similar (slightly better) to 2011-2013 Validating OMI measurements against ozonesondes (2011-2013)

22. OMI ozone data quality is not significantly degraded from 2008