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HTAP Multi-model Assessment of Ozone Source-receptor Relationships

This draft interim report presents a detailed multi-model assessment of intercontinental ozone source-receptor relationships using a variety of 3-D models and simulations. The study evaluates the impact of emission reductions on surface ozone concentrations across different receptor regions, shedding light on the complexities and uncertainties associated with ozone transport. This informative report aims to enhance understanding in order to inform future negotiations under the CLRTAP Convention.

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HTAP Multi-model Assessment of Ozone Source-receptor Relationships

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  1. HTAP Multi-model Assessment of Ozone Source-receptor Relationships Arlene M. Fiore (arlene.fiore@noaa.gov) Kees Cuvelier, Frank Dentener (JRC) and the TF HTAP Modeling Team including Rokjin Park (GEOS-Chem v7.0 2x2.5) and Marta Garcia Vivanco (GEOS-Chem 4x5) Draft interim report at www.htap.org 3rd GEOS-Chem Users’ Meeting, Harvard University April 13, 2007

  2. TF HTAP mission: Develop a fuller understanding of hemispheric transport of air pollution to inform future negotiations under CLRTAP Convention on Long-Range Transboundary Air Pollution (CLRTAP) 49 parties in Europe, North America, and Central Asia Co-chairs: Terry Keating (U.S. EPA) and André Zuber (EC) TF HTAP Products: 2007 (Interim) and 2009 (Final) Assessment reports

  3. Thin dashes: seasonal mean Thick dashes: events Solid bars: annual means Literature Estimates of Surface O3 Enhancements at Northern Mid-latitudes from Hemispheric Transport RECEPTOR REGIONS USA EU ASIA SOURCE REGIONS: N. AMERICAEUROPEASIABACKGROUND Estimates are from studies cited in current draft of TF HTAP interim report Ch5, updated from tables in Holloway et al., ES&T, 2003 and Fiore et al., EM, 2003 Difficult to conduct meaningful assessment due to differences in: 1) methods 2) regional definitions 3) reported metrics

  4. EU NA EA SA HTAP Multi-model approach to estimate intercontinental source-receptor (S-R) relationships for ozone Conduct base simulations with 3-D models  horizontal resolution of 4°x5° or finer  2001 meteorology  each group’s best estimate for emissions in 2001  methane set to a uniform value of 1760 ppb Conduct sensitivity simulations(17 total) 20% decreases in: • anthrop. emis. in HTAP regions for NOx, CO, NMVOC individually • anthrop. emis. of all O3 and aerosol precursors in HTAP regions • global CH4

  5. Surface O3 seasonal cycles in base simulations over the HTAP regions 17-model mean 17-model range GEOS-Chem 2x2.5 GEOS-Chem 4x5 Other HTAP O3 models: CAMCHEM ECHAM5-HAMMOZ EMEP FRSGCUCI GEMAQ INCA LLNL-IMPACT-T5a MOZARTGFDL MOZECH OsloCTM2 STOC-HadAM3 STOCHEM TM5-JRC ULAQ UM-CAM EU NA Surface O3 (ppbv) EA SA Month of 2001  Model range often spans ~15 ppbv

  6. Recent ACCENT multi-model surface O3 vs. observations in HTAP regions: NA and EU North America OBS Multi-model mean standard deviation range SW US: 11 sites SE US: 12 sites US Great Lakes: 13 Europe and North Africa C. Mediterranean: 21 C. Europe: 101 sites Middle East: 1 site 25 participating models Year 2000 Ellingsen et al., in prep

  7. x x x x x x x x x GEOS-Chem 2x2.5 x GEOS-Chem 4x5 Estimates of S-R relationships: Annual mean surface ozone decrease due to 20% global methane reduction 2.0 1.5 1.0 0.5 0.0 Full range of 14 models ppbv EUROPE N. AMER. S. ASIA E. ASIA HTAP receptor region • 1 ppbv O3 decrease over all NH receptor regions • Consistent with prior studies What causes the ~1 ppbv range across individual models? -- examine ozone production efficiency; NOx:VOC ratios

  8. Estimates of S-R relationships: Sensitivity of surface O3 to NOx sources during season of max domestic O3 production 14 model range x GEOS-Chem x x x x x x x x x x x x x x x x x x x x S(20% decreases in foreign NOx) 20% decrease in domestic NOx = 10-30% Source region: Largest HTAP influence on SA Similar impact from all 3 foreign source regions Smallest HTAP influence on NA Largest S-R pair: NAEU Decrease in surface O3 (ppbv) Receptor region: Season:JJA JJA SON JJA • Examine springtime when intercontinental transport typically peaks • Compare role of NOx emissions with other O3 precursors

  9. SOURCE REGIONS: S 3 foreign regions S(-20% foreign emis.) -20% domestic emis. S(-20% foreign emis.) -20% domestic emis. ≈ 85% ≈ 55% RECEPTOR = EAST ASIA EU and NA ≥ SA Larger uncertainty in role of foreign VOC ppbv Estimates of S-R relationships: Springtime surface O3 decrease in HTAP receptor regions from 20% reductions of O3 precursors RECEPTOR = NORTH AMERICA EA/EU contribute similarly EU VOC at least as important as NOx ppbv

  10. Some remaining questions...(to be examined as part of the TF HTAP project) Overall conclusion from previous analysis: Range of estimates narrows from that in the literature under HTAP setup • Which processes contribute most to uncertainty in S-R relationships? • Insights from idealized tracer experiments • Normalize model response to emission perturbations • How can we best test models of hemispheric transport of air pollution?  Need to test processes (export, chemical evolution, mixing to surface) • Can 20% emission decreases be scaled to reductions of other magnitudes?  Yes for CH4; simulations underway for other O3 precursors • Role of hemispheric transport in polluted vs. background conditions?  Examine range of model responses across the O3 distribution • How will climate change affect hemispheric transport of air pollution? www.htap.org for more info and to comment on draft 2007 interim report

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