Ozone in the Troposphere Air Quality Chemical Weather

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

Why are we Interested in Tropospheric Ozone? Pollution: O 3 is an important component of photochemical smog Tropospheric oxidation: O 3 regulates oxidation through control of OH and controls removal of CH 4, VOCs, etc. Climate: Direct: O 3 is a greenhouse gas Indirect: O 3 governs lifetime of other GHGs via OH Anthropogenic Influence: Surface and Tropospheric O 3 is increasing due to human activity • 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

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)

Processes Controlling Tropospheric O 3 O 3 Strat. -Trop. Exchange NMHCs, CH 4, CO OH HO 2, RO 2 NO NO 2 hν Emissions CO, O 3 O 3 Deposition hν OH HO 2 H 2 O O 3

Processes Controlling Tropospheric O 3 O 3 Strat. -Trop. STE: Governed by meteorological Exchange systems, filamentation and mixing NMHCs, CH 4, CO OH HO 2, RO 2 NO NO 2 hν Emissions CO, O 3 hν production is non. Chemistry: O 3 O OH HO 3 linear; strongly location-dependent 2 H 2 O O 3 Deposition: dependent on highly Deposition variable surface environment

FRSGC/UCI Global CTM Wild and Prather [2000] Wild and Akimoto [2001] Wild et al. , [2003] 2 50 100 Pressure /h. Pa 200 400 600 Strat-Trop Exchange Strat. Chemistry: Linoz Cloud Formation Lightning NOx source Convection: Tiedke Photolysis: Fast-J Advection: 2 nd o. M Tropospheric Chemistry PBL Turbulence 800 1000 Surface Processes ASAD, 37 species Emissions Deposition 37 Levels T 42 resolution (2. 8°x 2. 8°); driven with ECMWF-IFS forecast fields

1. Intercontinental Transport of Ozone Current Industrial/Fossil Fuel NOx Emissions • 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

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

East Asian Emissions Source. Receptor Matrix 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

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 NOx/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

Ozone Responses Look at regional and global O 3 from a single day’s 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

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

Ozone Response to Shanghai Emissions Global Ozone Increase Regional Boundary Layer Distant Boundary Layer Free Troposphere • 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 • P(O 3) vs. NOx loss for each day – O 3 production efficiency (OPE) strongly dependent on location – Good representation of lifting processes is required!

3. Exploring the Uncertainty in Current CTMs O 3 Burden vs. O 3 Lifetime Diagonals in grey show O 3 loss rate (Tg/year) (τO 3 = Burden/Loss) • ACCENT studies • CTM with NMHC • CTM without NMHC • 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

3. Exploring the Uncertainty in Current CTMs O 3 Burden vs. O 3 Lifetime 330 Tg/yr Diagonals in grey show O 3 loss rate (Tg/year) (τO 3 = Burden/Loss) • ACCENT studies • CTM with NMHC • CTM without NMHC 22. 4 days Best estimates from recent model studies • 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

3. Exploring the Uncertainty in Current CTMs O 3 Burden vs. O 3 Lifetime Diagonals in grey show O 3 loss rate (Tg/year) 800 Tg STE 60 Tg NOx 650 Tg Isop 7. 5 Tg NOx lightning 460 Tg dep − 20% Sensitivity to key variables explains much of the scatter T− 5°C T+5°C 975 Tg dep +20% 30 Tg NOx +20% H 2 O 0 Tg 250 Tg STE 0 Tg − 20% H 2 O

3. Exploring the Uncertainty in Current CTMs • ACCENT studies • CTM with NMHC • CTM without NMHC • Summary of key sensitivities – – Account for 2/3 of NOx emissions: more O 3, P(O 3), more OH model variability Isoprene emissions: more O 3, P(O 3), less OH Lightning NOx: 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!

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 Climate aerosol NOx, CO VOC O 3 VOC NOy NO Soils Requires improved treatment of biogenic emissions and deposition. Crops Involves collaboration with land use and vegetation community and a full Earth System approach

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 These processes function on a range of scales, but their impacts on climate have not been assessed. Plume Mixing zone Wind Direction Involve strong collaboration with the UK and EU urban & local modelling community

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

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

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

r 2=0. 92 OPE=35

Evolution of O 3 profile over Cheju, Korea in CTM TRACE-P Ozonesondes – Very different profiles Pressure /h. Pa • Stratospheric intrusion at Cheju, Korea, March 1– 2, 2001 • Intercepted by sondes on successive days Tropopause • 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 Sonde data: Sam Oltmans, NOAA/CMDL March 1, 2001 March 2, 2001

Net O 3 Production Rate • Instantaneous O 3 production in CTM vs. box model constrained by observations • Mean latitude-altitude profile over all DC 8/P 3 B 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. )