Implications of observed surprisingly high atmospheric oxidizing capacity over tropical forest: the GABRIEL Campaign Laurens Ganzeveld 1,2, Tim Butler 2, John Crowley 2, Terry Dillon 2, Gunter Eerdekens 2,3, Horst Fischer 2, Hartwig Harder 2, Rainer Königstedt 2, Dagmar Kubistin 2, Mark Lawrence 2, Monika Martinez 2, Bert Scheeren 4, Vinayak Sinha 2, Domenico Taraborrelli 2, Jonathan Williams 2, Jordi Vilà-Guerau de Arellano 1, and Jos Lelieveld 2 1 Department of Environmental Sciences, Wageningen University and Research Centre, Wageningen, Netherlands 2 Department of Atmospheric Chemistry, Max-Plank Institute for Chemistry, Mainz, Germany 3 Research Group Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Antwerp, Belgium 4 European Commission Joint Research Centre, Institute for Environment and Sustainability, Climate Change Unit, Ispra, Italy. Laurens Ganzeveld 1,2, Tim Butler 2, John Crowley 2, Terry Dillon 2, Gunter Eerdekens 2,3, Horst Fischer 2, Hartwig Harder 2, Rainer Königstedt 2, Dagmar Kubistin 2, Mark Lawrence 2, Monika Martinez 2, Bert Scheeren 4, Vinayak Sinha 2, Domenico Taraborrelli 2, Jonathan Williams 2, Jordi Vilà-Guerau de Arellano 1, and Jos Lelieveld 2 1 Department of Environmental Sciences, Wageningen University and Research Centre, Wageningen, Netherlands 2 Department of Atmospheric Chemistry, Max-Plank Institute for Chemistry, Mainz, Germany 3 Research Group Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Antwerp, Belgium 4 European Commission Joint Research Centre, Institute for Environment and Sustainability, Climate Change Unit, Ispra, Italy.

De GABRIEL campagne (Guyana’s 2005) Lelieveld, J., Butler, T.M., Crowley, J., Dillon, T., Fischer, H., Ganzeveld, L., Harder, H., Kubistin, D., Lawrence, M.G., Martinez, M., Taraborrelli, D., and Williams, J., Atmospheric oxidation capacity sustained by a tropical forest, Nature, doi: /nature06870, Observations of OH concentrations in the PBL much higher than simulated in any state-of-the-art atmospheric chemistry and transport model. Surprisingly high atmospheric oxidizing capacity over tropical forest: the GABRIEL Campaign OH recycling in isoprene oxidation product reactions

urban (U.S.) remote agricultural (U.S.) Maritime (pacific) Courtesy: Franz Meixner, from: Chameides  O 3 production, OH recycling Oxidizing capacity The OH Radical: the Atmosphere‘s detergent OH HO 2 recycling source sink NMHC CO, CH 4, CH 2 O CO 2, H 2 O CH 2 O hνhν H2O2H2O2 HO 2 NO 2 NO hνhν NO 2 O 3 + hv O( 1 D) + H 2 O Primary OH Formation OH Recycling Wet tropical forest Oxidizing capacity NO x : reactive nitrogen oxides NO, NO 2, NO 3, etc. VOC’s (or NMVOC): Volatile Organic Compounds, e.g., isoprene, acetone etc.

Courtesy: Jos Lelieveld Oxidizing capacity Low NO x, high natural VOC’s

Major influences on tropospheric OH ForcingMechanismResponse NO x ↑O 3 formation, OH recyclingOH ↑ H 2 O ↑H 2 O + O( 1 D) → 2OHOH ↑ CH 4 ↑CH 4 + OH → productsOH ↓ CO ↑CO + OH → productsOH ↓ NMHC ↑NMHC + OH → productsOH ? Clouds ↑light scattering, multiphase chemistryOH ? Courtesy: Jos Lelieveld How will deforestation affect atmospheric chemistry and climate through the modification of the exchange of moisture, energy and matter and GHG lifetime? Oxidizing capacity

 Note the large difference between simulated and observed OH concentrations < 1500m  This points at a problem in atmospheric chemistry models in the representation of boundary layer chemistry and in particular of tropical forest exchanges  It explains why large-scale scale chemistry models overestimate tropical isoprene concentrations using state-of-the art biogenic emission algorithms Factor 5-10 higher OH concentraties in tropical BL  10-20% decrease in CH 4 lifetime The other cleansing mechanism; wet deposition

GABRIEL flight tracks Atmospheric Chemistry over tropical forest: Gabriel flight tracks

Single-Column Chemistry-Climate model Multi-layer canopy model for trace gas exchanges CBM4+ terpene chemistry, sulfur, CH3CL and Rn Multi-layer canopy model for trace gas exchanges CBM4+ terpene chemistry, sulfur, CH3CL and Rn GABRIEL flight tracks and SCM trajectory for lagrangian experiment 4.5N, 45W-60W : :00 UTC ΔT=60 seconds, 6.5 m s -1 (z ref =1250m), ΔX = ~ 300 m Atmospheric Chemistry over tropical forest: SCM simulations Ganzeveld, L., and J. Lelieveld, Impact of Amazonian deforestation on atmospheric chemistry, Geophys. Res. Lett., 31, L06105, doi: /2003GL019205, 2004.

Sources of Reactive Trace Gases: NO x -VOC Simulated soil NO emissions and canopy NOx flux Simulated isoprene emissions for Gabriel domain Inferred isoprene emission flux from dC/dt in C 5 H 8 and MVK+Methac. conc and PBL height Extensive evaluation of BVOC and NO x exchanges regime Ganzeveld, L., Eerdekens, G., Feig, G., Fischer, H., Harder, H., Königstedt, R., Kubistin, D., Martinez, M., Meixner, F. X., Scheeren, B., Sinha, V., Taraborrelli, D., Williams, J., Vilà-Guerau de Arellano, J., and Lelieveld, J., Surface and Boundary Layer Exchanges of Volatile Organic Compounds, Nitrogen Oxides and Ozone during the GABRIEL Campaign, Atmos. Chem. Phys., 8, 6223–6243, 2008.

Simulated OH source and sink terms over tropical forest Simulated chemical sources and sinks of OH over land, day2, 18UT OH –C 5 H 8 jO 3 Simulated versus observed OH concentrations over land PBL Representation of jO 3 in FT is explaining a lot of discrapency but in PBL there is still a large underestimation: too large sink or missing source of OH in PBL?

OH concentrations in canopy and PBL Elevated nocturnal and early morning OH sesquiterpene concentrations in canopy and PBL OH sources: VOC ozonolysis Considering this potential source of OH improves the simulations of OH and isoprene in the canopy and surface layer but not aloft! Needed: VOC being destroyed by ozonolysis (not by OH), producing efficiently OH and living long enough to be transported higher up in the PBL (τ ~30 min.)

Compound τOH [OH]=2e 6 cm -3 τO 3 [O 3 ]=7e 11 cm -3 OH yield2-generation Product with Double Bond isoprene1.4 h1.3 day  -pinene 2.6 h4.6 h  -pinene 1.8 h1.1 day carene1.7 h 3-carene1.6 h11 h limonene49 min2.0 h x sabinene1.2 h4.8 h myrcene39 min50 min xx cis/trans-ocimene33 min44 min xx  -phellandrene 27 min 8 min?  -phellandrene 50 min8.4 h0.14x  -terpinene 23 min 1 min0.38  -terpinene 47 min2.8 h0.81 terpinolene37 min 13 min x  -caryophyllene 42 min 2 min0.06x  -cedrene 2.1 h14 h  -copaene 1.5 h2.5 h  -humulene 28 min 2 min?xx longifolene2.9 h> 33 day linalool52 min 55 min x 6 methyl-5-heptene-2-one53 min 1.0 h0.75 high OH yield, sink of OHhigh OH yield, source of OH, and τO3 ~ τTurbulent OH yield? source of OH, but τO 3 << τTurbulent OH sources: VOC ozonolysis

OH-C 5 H 8, ~ -25 in surface layer O 3 -terpinolene Terpinolene brings some more OH higher up in the PBL: However this is for an emission flux of terpinolene of 10 x monoterpene emission flux This resembles a reactive alkene emission flux comparable to that of isoprene! OH sources: VOC ozonolysis jO 3 OH recycling in isoprene oxidation product reactions

Simulated chemical sources and sinks of OH over land, day2, 18UT Substantial overstimation HCHO OH sinks: other compounds besides isoprene CO Reasonable agreement in PBL H2O2H2O2 Good agreement

Simulated HCHO concentrations for L60, Femisop=0.25 Nocturnal build-up of isoprene oxidation products such as HCHO, MVK, Methac., etc.: How significant is this residual layer chemistry for daytime chemistry and exchanges? Precursors and oxidation products: HCHO

Conclusions and outlook  Gabriel observations have indicated that the oxidizing capacity over pristine tropical forest is substantially larger then previously assumed  This (partly) explains the misrepresention of C 5 H 8 concentrations in ACTMs and is expected to have a significant impact of the lifetime of CH 4 and pollutants (and aerosol production?)  The actual mechanims that explains this much larger OH concentration is still under investigation focussing on reactions involving isoprene oxidation products  However, interpretation of the observations has also revealed an potentially important role of longer-lived compounds with chemical transformations occuring in the nocturnal inversion- and residual layer  Future AC campaigns; nocturnal observations including airborne/tetherered balloon observations to reach residual layer

Thank you !