What will control future tropospheric ozone? David Stevenson + thanks to many others, acknowledged along the way

Tropospheric Ozone (O 3 ) Not to be confused with stratospheric ozone (same gas, different place)

About ¼ of CO 2 forcing

US EPA (1999) Ozone the air pollutant: Los Angeles smog 1950s Ozone linked to respiratory diseases, e.g., asthma

O 3 injury to wheat, Pakistan (courtesy of A. Wahid) Ozone damages crops Ozone impact Chamber impact

Ozone impact on vine leafs Soja et al. (2004) OTC experiments 30 km Vienna, Austria 4 treatments, CF, NF, +25 ppb, +50 ppb Exposed for 3 years Non-filtered (NF) air i.e. ambient Courtesy Lisa Emberson, Stockholm Environment Institute, University of York

Ozone is a secondary pollutant i.e., unlike CO 2, CH 4, etc., it is not directly emitted It is generated in the atmosphere from its precursors by photochemical reactions In addition there are important physical and biological processes that control its distribution A brief summary of the main chemical and physical processes…

‘Odd oxygen’ O 3 + h → O( 3 P) + O 2 O( 3 P) + O 2 + M → O 3 O 3 + h → O( 1 D) + O 2 O( 1 D) + M → O( 3 P) O3O3 NO 2 NO Stratospheric O 3 Dry deposition O( 3 P) O( 1 D) O 3 + NO → NO 2 + O 2 NO 2 + h → O( 3 P) + NO HO 2 OH CO CH 4 VOC Anthropogenic & Natural emissions NO y losses Tropospheric Ozone Chemistry Surface Stratosphere Troposphere 10-15km O 3 losses +H 2 O ΔClimate

Relevant timescales for O 3 Chemical lifetime of O 3 : – weeks-months in upper troposphere – days-weeks in lower troposphere Tropospheric transport and mixing: –vertical convection: minutes-hours –synoptic meteorology: days –intercontinental transport: days-weeks –interhemispheric transport: ~1 year Chemical and transport timescales overlap: both processes are important

Tropospheric O 3 essentials Its not stratospheric ozone Greenhouse gas (¼ forcing of CO 2 since 1850) –Concentrations +50 to +100% since 1850 –(but its not in the Kyoto Protocol) Secondary air pollutant: –Precursors: NO x, CO, CH 4, VOCs (+sunlight) –Linked to respiratory diseases, e.g. asthma –Damages crops (One estimate: £3bn/yr in Europe) –Also harms forests, natural ecosystems Lifetime ~weeks → regional distribution Ozone is not only a climate issue, but also affects the wider environment & economy

ACCENT model intercomparison for IPCC-AR4 25 different models perform same experiments –15 Europe: 4 UK (Edinburgh, Cambridge x2, Met. Office) 3 Germany (Hamburg x2, Mainz) 2 France (Paris x2) 2 Italy (Ispra, L’Aquila) 1 Switzerland (Lausanne) 1 Norway (Oslo) 1 Netherlands (KNMI) 1 Belgium (Brussels) –7 US –3 Japan Large ensemble reduces uncertainties, and allows them to be quantified

Future tropospheric O 3 Consider 2030 – ‘the next generation’ – of direct interest for policymakers 3 Emissions scenarios –‘Likely’: IIASA CLE (‘Current Legislation’) –‘High’: IPCC SRES A2 –‘Low’: IIASA MFR (‘Maximum technically Feasible Reductions’) Also assess climate feedbacks –expected surface warming of ~0.7K by 2030

People & Organisation Co-ordination; N+S-deposition, Tropospheric O 3 –F. Dentener, D. Stevenson Surface O 3 - impacts on health/vegetation; web-site –K. Ellingsen NO 2 columns – comparison of models and satellite data –T. van Noije, H. Eskes Emissions –M. Amann, J. Cofala, L. Bouwman, B. Eickhout Data handling and storage (SRB; ~1 TB of model output) –J. Sundet Other modellers and contributors: –C.S. Atherton, N. Bell, D.J. Bergmann, I. Bey, T. Butler, W.J. Collins, R.G. Derwent, R.M. Doherty, J. Drevet, A. Fiore, M. Gauss, D. Hauglustaine, L. Horowitz, I. Isaksen, M. Krol, J.-F. Lamarque, M. Lawrence, V. Montanaro, J.-F. Müller, G. Pitari, M.J. Prather, J. Pyle, S. Rast, J. Rodriguez, M. Sanderson, N. Savage, M. Schultz, D. Shindell, S. Strahan, K. Sudo, S. Szopa, O. Wild, G. Zeng

Year 2000 Anthropogenic NO x Emissions EDGAR database: Jos Olivier et al., RIVM Plot: Martin Schultz, MPI

Year 2000 tropospheric NO 2 columns Model (ensemble mean) Observed (GOME) (mean of 3 methods) Courtesy Twan van Noije, Henke Eskes (10:30am local sampling in both cases)

Global NO x emission scenarios Figure 1. Projected development of IIASA anthropogenic NO x emissions by SRES world region (Tg NO 2 yr -1 ). CLE SRES A2 MFR

Figure 4. Regional emissions separated for sources categories in 1990, 2000, 2030-CLE and 2030-MFR for NO x [Tg NO 2 yr -1 ] Regional NO x emissions CLE 2030 MFR Europe: falling Asia: rising USA: ~flat Biomass burning important source for Africa / S. America Ships/aircraft: unregulated; may become larger than any regional source by 2030

Emission Changes 2030 CLE Plots: Martin Schultz, MPIIIASA RAINS model: Markus Amann et al.

Year 2000 Annual Zonal Mean Ozone (24 models)

Year 2000 Ensemble mean of 25 models Annual Zonal Mean Annual Tropospheric Column

Year 2000 Inter-model standard deviation (%) Annual Zonal Mean Annual Tropospheric Column

Comparison of ensemble mean model with O 3 sonde measurements J F M A M J J A S O N D Observed ±1SD Model ±1SD 90-30°S 30°S-Eq30°N-Eq90-30°N UT 250 hPa MT 500 hPa LT 750 hPa

2030 CLE MRF A ppbv-5 ppbv+10 ppbv

Tropospheric O 3 scales ~linearly with NO x emissions

Radiative forcing implications Forcings (mW m -2 ) for the 3 scenarios: -23% +37% CO 2 CH 4 O3O3

Impact of Climate Change on Ozone by 2030 (ensemble of 9 models) Mean Mean - 1SD Mean + 1SD Negative water vapour feedback Positive stratospheric influx feedback Positive and negative feedbacks – no clear consensus

Impact-based ozone indices: AOT40 Accumulated over crop growing season (e.g. 3 months for wheat) Courtesy Lisa Emberson

3000 ppb.h !!! AOT40, May-June-July, mean model, ppb*hours

Change in AOT40 (CLE)

Change in AOT40 (MFR)

Change in AOT40 (A2)

Conclusions Tropospheric O 3 will increase over most parts of the world by 2030, following a ‘Current Legislation’ scenario (some view this as relatively optimistic) O 3 could be reduced if current emissions reduction technologies were applied worldwide (wildly optimistic) O 3 could rapidly rise under a high growth scenario with lax emissions controls, reminding us of the consequences of not implementing current policies (pessimistic) Reductions would have clear (and quantifiable) benefits for climate and air quality; increases have clear detrimental impacts. Climate change is likely to have both positive and negative feedbacks on ozone – model predictions are rather uncertain as to which feedbacks dominate. There a clear synergies between climate and air pollution control policies that should be exploited.