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The Influence of biogenic emissions on tropospheric ozone over Equatorial Africa during 2006

The Influence of biogenic emissions on tropospheric ozone over Equatorial Africa during 2006. J.E. Williams, R. Scheele, P.F.J. van Velthoven, J-P. Cammas, V. Thouret, C. Lacy-Galeux and A. Völz-Thomas. Questions within the AMMA project How well can a state-of-the-art global 3D CTM

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The Influence of biogenic emissions on tropospheric ozone over Equatorial Africa during 2006

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  1. The Influence of biogenic emissions on tropospheric ozone over Equatorial Africa during 2006 J.E. Williams, R. Scheele, P.F.J. van Velthoven, J-P. Cammas, V. Thouret, C. Lacy-Galeux and A. Völz-Thomas

  2. Questions within the AMMA project • How well can a state-of-the-art global 3D CTM capture the seasonality and variability of trace gas species in the African Troposphere. • Have improvements been made to the recent emission estimates which influence the performance of the model?? • What governs the oxidizing potential of this region?? • How do biogenic emissions from Africa influence the oxidative capacity of the global troposphere?? The Biogenic Emission study

  3. Driven by ECMWF operational data (6hrly). • Lumped chemical mechanism : modified • CBM4 (38 species) HOx-NOx-CO-CH4 • Organics introduced using the chemical • groups (C=C, CHO, etc). • Heterogeneous oxidation of SO2, N2O5, NH3 • Used in many previous studies including • multi-model intercomparisons. • 34 model layers (1km resolution in UT/LS) • 3 x 2  horizonzal resolution • Emissions: Anthropogenic (RETRO project) • Biomass burning (GFEDv2) • Biogenics (POET vs Lathiere) The TM4 Model

  4. Biogenic NO emissions Regions: (_) Saharan (40-20°N), (_) Sahel (10-20°N), (_) Guinea (0-10°N), and (_) southern Africa(40-0°S) Yienger and Levy (1995) vs Lathiére et al (2006)

  5. Isoprene Emissions (incl monoterp) Regions: (_) Saharan (40-20°N), (_) Sahel (10-20°N), (_) Guinea (0-10°N), and (_) southern Africa (40-0°S) Guenther et al (1995) vs Lathiere et al (2006)

  6. Volatile Organic Compounds Regions: (_) Saharan (40-20°N), (_) Sahel (10-20°N), (_) Guinea (0-10°N), and (_) southern Africa (40-0°S) Additional VOC’s : CH3COOH, HCHO and CH3CHO Different inventories: Acetone, C2H5OH

  7. Percentage differences in annual global fluxes for Africa Fraction = LATH/POET Longitudinal differences not shown but emission regions do shift with season

  8. Sensitivity studies 34 layers,3° x 2°, ECMWF 6 hour re-analysis LiNOx identical, 3 months spin-up

  9. LATH-POET/LATH • [O3] shows regionalsimilarities with [NO]↑ • (c.f. DJF – s.Africa). • [Isoprene] signature when [NO]↑ is ~ equal. • (c.f. MAM – s.Africa) • In the absence of strong [NO]↑ less [O3] in LATH.

  10. LATH-POET/LATH [PAN] shows regional similarities with [Isoprene]↑ (10S-10N). Source of CH3C(O)O2 Low in Sahara. Weaker [PAN] on [NO] ↑

  11. LATH-POET/LATH [HNO3] shows regional similarities with [O3] O3 + h (+H2O)  2OH OH + NO2  HNO3 5% More N deposition as HNO3 adds to decreases in [O3] for the background

  12. LATH-POET/LATH [OH] shows regional similarities with [O3] O3 + h (+H2O)  2OH In general the oxidizing power of the atmosphere decreases when using the LATH inventory

  13. LATH-NOSOIL/LATH • [NO] from soils has a large impact on tropospheric [O3] near the source regions • Differences extend throughout the troposphere • The maximum differences follow the seasonality of the NO emissions

  14. Δ[PAN] from African Soil NOx

  15. Δ[O3] from African soil NOx

  16. Δ[O3] in Tropical Troposphere African soil NOx influences the Total Tropical Ozone Column by 5-10% over the Atlantic

  17. MOZAIC profiles from Windhoek (22.5°S, 17.5°E) • LATH agrees better with MOZAIC profiles • Largest diff • shown by NOSOIL run • Effect of soil NOx propagates up the column High Soil NOx in DJF (_) POET, (_) LATH, (_) NOSOIL, (_) OBS

  18. MOZAIC in-flight data over Africa  Soil NOx High [O3] over biomass burning regions is not captured (_) POET, (_) LATH, (_) NOSOIL, (_) OBS,(_) STRAT

  19. 25.9°S 28.2°E 6.6°N 2.2°E 1.3°S 36.8°E Very High O3 Values near Lagos (_) POET, (_) LATH, (_) NOSOIL, (_) OBS

  20. French and German Falcons + UK BAe146 No simulation captures the high [O3] in measurements Lack of variation in soil NO emission between measurements Low [O3] captured when soil NO off!

  21. Comparison with IDAF ground sites : [O3] Dry Site location: 0-15N 10W-10E TM4 generally over-estimates surface [O3] in remote regions by 50-100% Transport of [O3] into measurement site dominates 2-5% stratospheric origin Wet Savannah Forest (_) POET, (_) LATH, (_) NOSOIL, (_) OBS

  22. Comparison with IDAF ground sites : [NO2] Dry Site location: 0-15N 10W-10E Both POET and LATH over predict [NO2] For some stations soil NO emissions account for nearly 100% of the resident [NO2]. Forest Wet Savannah (_) POET, (_) LATH, (_) NOSOIL, (_) OBS

  23. Comparison with IDAF ground sites : [HNO3] Dry Location: 0-15N 10W-10E Generally too [HNO3] is too low for many months but [O3] and [NO2] both too high. OH + NO2 HNO3 Why [HNO3] is low ?? Linked to missing OH source or exaggerated sink?? Wet Savannah Forest (_) POET, (_) LATH, (_) NOSOIL, (_) OBS

  24. Chemical Budget : Global Oxidizing capacity African soilNOxlarge affect on CH4 and CO 50% BB CO from Africa thus reducing OH increases transport and lifetime (Jain, 2007) LATH vs POET ; NOSOIL/NOBIO vs LATH

  25. Tropical Chemical Budget for BVOC’s LATH vs POET ; NOSOIL/NOBIO vs LATH • Biogenic emissions of ALD2 and HCHO are insignificant • Doubling of alkanes (PAR) using LATH (~4% globally) • Biogenic NO responsible for oxidizing 20% of trop [ISOP] via O3/OH • Biogenic BVOC’s reduces [OH] moderately

  26. Conclusions • The new biogenic climatology results in moderate improvements to TM4 cf MOZAIC measurements • The new biogenic climatology results in a less oxidising atmosphere increasing lifetime of greenhouse gases by ~2% (CH4) and ~4% (CO) • NO emissions from soils have a large effect on the African troposphere upto the UT/LS (30-50% trop. [O3] directly formed from this source, ~20% [ISOP] oxidation) • Updated frequency of emission inventory and extension of simulation period has potential to improved tropical O3 in global CTM´s • Future Climate: Drier environment reduces soil NO thus potentially increasing CH4 and CO Appearing in ACPD in the next few weeks

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