1. Ozone in the Troposphere: Air Quality, Chemical Weather and Climate Oliver Wild Centre for Atmospheric Science, Cambridge Dept. of Environmental Science, University of Lancaster, 5 th June 2007

2. Why are we Interested in Tropospheric Ozone? Environmental impacts on local, regional and global scales Secondary pollutant: sensitive to many variables –Chemical production can be fast in polluted conditions –Lifetime is sufficiently long for global-scale transport Pollution: O 3 is an important component of photochemical smog Climate: Direct:O 3 is a greenhouse gas Indirect:O 3 governs lifetime of other GHGs via OH Tropospheric oxidation: O 3 regulates oxidation through control of OH and controls removal of CH 4, VOCs, etc. Anthropogenic Influence: Surface and Tropospheric O 3 is increasing due to human activity

3. Ozone in the Troposphere Intercontinental transport of O 3 from industrial sources –Very long-range transport and the global O 3 background Regional meteorology and its impacts on O 3 –How do physical processes govern chemistry and transport? Characterising the uncertainty in current chemistry models –Can we explain the observed trends in O 3 and CH 4 ? –What processes affecting O 3 are least well understood? Underlying themes: 1.Development and evaluation of tropospheric chemistry models 2.Thorough testing of models against atmospheric measurements 3.Application to air quality and climate issues (O 3 and CH 4 )

4. Processes Controlling Tropospheric O 3 NONO 2 OHHO 2 CO, O 3 O3O3 O3O3 H2OH2O hνhν HO 2, RO 2 hνhν Deposition Strat.-Trop. Exchange NMHCs, CH 4, CO Emissions O3O3 OH O3O3 O3O3

5. Processes Controlling Tropospheric O 3 NONO 2 OHHO 2 CO, O 3 O3O3 O3O3 H2OH2O hνhν HO 2, RO 2 hνhν Deposition Strat.-Trop. Exchange NMHCs, CH 4, CO Emissions O3O3 OH O3O3 O3O3 STE: Governed by meteorological systems, filamentation and mixing Deposition: dependent on highly variable surface environment Chemistry: O 3 production is non- linear; strongly location-dependent

6. FRSGC/UCI Global CTM 1000 100 2 800 600 400 200 T42 resolution (2.8°x2.8°); driven with ECMWF-IFS forecast fields Pressure /hPa Emissions Wild and Prather [2000] Wild and Akimoto [2001] Wild et al., [2003] Deposition Tropospheric Chemistry ASAD, 37 species Strat. Chemistry: Linoz PBL Turbulence Convection: Tiedke Advection: 2 nd oM Strat-Trop Exchange Photolysis: Fast-J Cloud FormationLightning NO x source Surface Processes 37 Levels 50

7. 1. Intercontinental Transport of Ozone Industrial emission regions located at similar latitudes –Transport times about 1 week; chemical lifetime 3-4 weeks How much do major emission regions affect each other? –How much do they contribute to background O 3 ? –Could this affect attainment of air quality standards? Explore O 3 production and transport with 3-D global CTM –Single-region anthropogenic emission perturbation experiments Current Industrial/Fossil Fuel NO x Emissions

8. Photochemistry active in summer Transport most efficient in spring Wild and Akimoto [2001] Largest O 3 impacts in late spring

9. Source- Receptor Matrix East Asian Emissions US Emissions European Emissions Major emission regions directly affect each other –Upwind sources contribute 1-2 ppbv to surface background O 3 –This is sufficient to affect attainment of air quality standards –Study now being repeated with many models (HTAP) to inform policy

10. 2. Regional Meteorology and Chemical Weather Key Questions and Challenges –How are regional and global impacts influenced by meteorology? What is the variability in O 3 production from a given source? –How does meteorology govern climate impacts of sources? How will future changes in meteorology affect climate impacts? –How well can models simulate the time scales for O 3 formation? Model Approach –Perturb fossil fuel NO x /CO/NMHC emissions over one region for one day Follow atmospheric perturbation for 1 month –Repeat for each day of March 2001 (TRACE-P measurement campaign) –Look at variability in magnitude and location of O 3 production

11. Ozone Responses Look at regional and global O 3 from a single days emissions over Shanghai March 12 –Sunny, high pressure –Strong regional P(O 3 ) March 16 –Heavily overcast –Little regional P(O 3 ) Regional production different, Global production similar –Evolution quite different –Location of P(O 3 ) different

12. Meteorological Setting on March 12 and 16, 2001 Column- and latitude-integrated gross O 3 production over the first 3 days following 1 day of emissions over Shanghai L H H L

13. Ozone Response to Shanghai Emissions Effects on O 3 burden –Days with high regional O 3 (smog) have a reduced effect on global O 3 –Regional meteorology strongly influences climate impacts Regional Boundary Layer Distant Boundary Layer Free Troposphere Global Ozone Increase Regional Ozone Increase P(O 3 ) vs. NO x loss for each day –O 3 production efficiency (OPE) strongly dependent on location –Good representation of lifting processes is required!

14. 3. Exploring the Uncertainty in Current CTMs CTM studies show large differences in O 3 burden and lifetime –Where do these differences originate? Perform sensitivity study on key processes in a single CTM –Identify processes contributing to this uncertainty O 3 Burden vs. O 3 Lifetime Diagonals in grey show O 3 loss rate (Tg/year) (τ O3 = Burden/Loss ) ACCENT studies CTM with NMHC CTM without NMHC

15. 3. Exploring the Uncertainty in Current CTMs CTM studies show large differences in O 3 burden and lifetime –Where do these differences originate? Perform sensitivity study on key processes in a single CTM –Identify processes contributing to this uncertainty O 3 Burden vs. O 3 Lifetime Diagonals in grey show O 3 loss rate (Tg/year) (τ O3 = Burden/Loss ) ACCENT studies CTM with NMHC CTM without NMHC 330 Tg/yr 22.4 days Best estimates from recent model studies

16. 3. Exploring the Uncertainty in Current CTMs Sensitivity to key variables explains much of the scatter 60 Tg NOx 650 Tg Isop 800 Tg STE 250 Tg STE 20% H 2 O +20% H 2 O 7.5 Tg NOx lightning T5°C T+5°C 0 Tg 460 Tg dep 975 Tg dep 20% +20% 30 Tg NOx O 3 Burden vs. O 3 Lifetime Diagonals in grey show O 3 loss rate (Tg/year)

17. 3. Exploring the Uncertainty in Current CTMs Summary of key sensitivities –NO x emissions: more O 3, P(O 3 ), more OH –Isoprene emissions: more O 3, P(O 3 ), less OH –Lightning NO x : poorly constrained, large impact on O 3 and OH –Meteorology: effects of humidity and STE Implications –Current models are not good enough to model trends in O 3 and CH 4 ! Account for 2/3 of model variability ACCENT studies CTM with NMHC CTM without NMHC

18. Future Studies Modelling atmosphere-vegetation interactions –Important feedbacks between O 3, VOC, N-species and plants –Interaction of anthropogenic and vegetation emissions is very poorly understood and requires spatial disaggregation –Currently lead the biogenic fluxes theme in JULES SoilsCrops Requires improved treatment of biogenic emissions and deposition. Involves collaboration with land use and vegetation community and a full Earth System approach NO x, CO VOC VOC aerosol O3O3 NO NO y Climate

19. Future Studies Improved treatment of urban emissions in climate models –Improved simulation of O 3 production in coarse-resolution models –Reduced bias in regional/global O 3 important for climate –Allows better testing against surface observations –Important for assessing environmental impacts of Megacities Background Plume Mixing zone These processes function on a range of scales, but their impacts on climate have not been assessed. Involve strong collaboration with the UK and EU urban & local modelling community Wind Direction

20. Future Studies Modelling the evolution of tropospheric oxidation –Reproducing the observed trends in CH 4 and O 3 –Important for climate and air quality communities –Requires improved understanding of tropospheric chemistry –Need a better characterization of variability in CH 4 sources Need more thorough testing of models vs. observations Contributes to goals of new international Atmospheric Chemistry and Climate project

22. Wild and Akimoto [2001] Annual Mean Impacts on O 3

23. Daily O 3 from Source Regions in Springtime Global Impact Receptor Region

24. r 2 =0.92 OPE=35

25. TRACE-P Ozonesondes Stratospheric intrusion at Cheju, Korea, March 1–2, 2001 Intercepted by sondes on successive days –Very different profiles CTM captures evolution of features well –Two layers on March 1 –Background strat. enhancement –One high layer on March 2 –Residual strat air mixed in Suggests mechanisms for STE can be captured, but demonstrates high degree of variability in ozone Evolution of O 3 profile over Cheju, Korea in CTM Pressure /hPa March 1, 2001March 2, 2001 Sonde data: Sam Oltmans, NOAA/CMDL Tropopause

26. Net O 3 Production Rate Instantaneous O 3 production in CTM vs. box model constrained by observations Mean latitude-altitude profile over all DC8/P3B flights Net destruction in tropical marine boundary layer Strong production over Japan Strong plume activity in outflow region, 23º–32ºN Net production in upper trop (underestimated in CTM) (Box model: Jim Crawford, NASA Langley, Doug Davis, Georgia Tech.)