Multi-model estimates for intercontinental transport of ozone pollution in the northern hemisphere(and uncertainties therein)

GFDL lunchtime seminar, January 21, 2009Arlene M. Fiore(arlene.fiore@noaa.gov)F. Dentener, O. Wild, C. Cuvelier, M. Schultz, D. Reidmiller, C. Textor, M. Schulz, C. Atherton, D. Bergmann, I. Bey, G. Carmichael, W. Collins, R. Doherty, B. Duncan, G. Faluvegi, G. Folberth, M. Garcia Vivanco, M. Gauss, S. Gong, D. Hauglustaine, P. Hess, T. Holloway, L. Horowitz, I. Isaksen, D. Jacob, D. Jaffe, J. Jonson, J. Kaminski, T. Keating, A. Lupu, I. MacKenzie, E. Marmer, V. Montanaro, R. Park, K. Pringle, J. Pyle, M. Sanderson, S. Schroeder, D. Shindell, D. Stevenson, S. Szopa, R. Van Dingenen, P. Wind, G. Wojcik, S. Wu, G. Zeng, A. Zuber

Reduced Visibility from Transpacific Transport of Asian DustGlen Canyon, Arizona, USAEvidence of intercontinental transport at northern midlatitudes: 2001 Asian dust eventDust leaving the Asian coast in April 2001Image c/o NASA SeaWiFS Project and ORBIMAGE

GEOS-Chem Model4x5 horizontal resolutionLi et al., JGR, 2002Hemispheric scale contribution of major source regions to summertime surface ozone: difficult (impossible?) to observe directlyEstimated with model simulations that zero out anthropogenic emissions of O3 precursors within the source regionNorth AmericaEuropeAsia

U.N. Economic Commission for EuropeConvention on Long-Range Transboundary Air Pollution (CLRTAP; established 1979)Co-chairs: Terry Keating (U.S. EPA) and Andr Zuber (EC)TF HTAP Mission: Develop a fuller understanding of hemispheric transport of air pollution to inform future negotiations under CLRTAP51 parties in Europe, North America, and Central Asia

Multi-model assessment involving >25 modeling groups HTAP S-R RegionsOBJECTIVES: Quantify S-R relationships for HTAP regions and assess uncertainties in these estimatesFocus species: Ozone and precursors Aerosols and precursors Mercury Persistent Organic Pollutants Idealized Tracers Oxidized NitrogenPRODUCTS: 2007 Interim Report to inform the review of the 1999 CLRTAP Gothenburg Protocol to abate acidification, eutrophication, and tropospheric ozone (www.htap.org). 2010 Assessment Report to inform the CLRTAP on hemispheric air pollution and S-R relationships.

Wide range in prior estimates of intercontinentalsurface ozone source-receptor (S-R) relationshipsAssessment hindered by different (1) methods, (2) reported metrics, (3) meteorological years, (4) regional definitions Few studies examined all seasonsASIA NORTH AMERICA NORTH AMERICA EUROPEannual mean eventsseasonal meanStudies in TF HTAP [2007] + Holloway et al., 2008; Duncan et al., 2008; Lin et al., 2008 eventsseasonal meanannual meanSurface O3 contribution from foreign region (ppbv)

Objective: Quantify & assess uncertainties in N. mid-latitude S-R relationships for ozoneBASE SIMULATION (21 models): horizontal resolution of 5x5 or finer 2001 meteorology each groups best estimate for 2001 emissions methane set to 1760 ppb

SENSITIVITY SIMULATIONS (13-18 models): -20% regional anthrop. NOx, CO, NMVOC emissions, individually + all together (=16 simulations) -20% global methane (to 1408 ppb)TF HTAP REGIONS

Large inter-model range; multi-model mean generally captures observed monthly mean surface O3 MediterraneanCentral Europe < 1kmCentral Europe > 1kmNE USASW USASE USAJapanMountainous W USAGreat Lakes USASurface Ozone (ppb)

North America as a receptor of ozone pollution: Annual mean foreign vs. domestic influences(1.64)Full range of 15 individual modelsAnnual mean surface O3 decrease from -20% NOx+CO+NMVOC regional anthrop. emissionsSum 3 foreigndomesticppbvimport sensitivity

North America as a receptor of ozone pollution: Seasonality of response to -20% foreign anthrop. emissionsSAEUEASUM OF 3 FOREIGN REGIONS15- MODEL MEAN SURFACEO3 DECREASE (PPBV)Spring (fall) max due to longer O3 lifetime, efficient transport [e.g., Wang et al., 1998; Wild and Akimoto, 2001; Stohl et al., 2002; TF HTAP 2007]

North America as a receptor of ozone pollution:Seasonality of response to -20% foreign anthrop. emissions CONOxNMVOCNOx+NMVOC+CO MODEL ENSEMBLE MEAN SURFACEO3 DECREASE (PPBV)Wide range in EU anthrop. NMVOC inventories large uncertainty in the estimated response of NA O3

North America as a receptor of ozone pollution: Seasonality in import sensitivity Surface O3 response to -20% domestic(NA NOx+NMVOC+CO) anthrop. emis.PPBRATIOResponse to -20% Foreign > Domestic(winter)

Surface O3 response to decreases in foreign anthropogenic emissions of O3 precursorsSource region: SUM3 NA EA EU SAEU receptorEA receptorSA receptorSurface O3 decrease (ppb)

Monthly mean import sensitivities

Surface ozone response to -20% global [CH4]:similar decrease over all regions Full range of 18 modelsppbEU NA E Asia S Asia 1 ppbv O3 decrease over all regions [Dentener et al.,2005; Fiore et al., 2002, 2008; West et al., 2007]Estimate O3 response to -20% regional CH4 anthrop. emissions to compare with O3 response to NOx+NMVOC+CO:

-20% global [CH4] -25% global anthrop. CH4 emissions Anthrop. CH4 emis. inventory [Olivier et al., 2005] for regional emissions Scale O3 response diagnosed with change in global burden to obtain O3 response due to regional CH4 emission change

Tropospheric O3 responds approximately linearly to anthropogenic CH4 emission changes across modelsAnthropogenic CH4 contributes ~50 Tg (~15%) to tropospheric O3 burden ~5 ppbv to surface O3Fiore et al., JGR, 2008

Comparable annual mean surface O3 response to -20% foreign anthropogenic emissions of CH4 vs. NOx+NMVOC+COppb(Uses CH4 simulation + anthrop. CH4 emission inventory [Olivier et al., 2005]to estimate O3 response to -20% regional anthrop. CH4 emissions) Sum of annual mean ozone decreases from 20% reductions of anthropogenic emissions in the 3 foreign regionsReceptor: NA EU E Asia S Asia

Summary: Hemispheric Transport of O3

Benchmark for future: Robust estimates + key areas of uncertainty

Import Sensitivities (D O3 from anthrop. emis. in the 3 foreign vs. domestic regions): 0.5-1.1 during month of max response to foreign emis; 0.2-0.3 during month of max response to domestic emissions

Comparable O3 decrease from reducing equivalent % of CH4 and NOx+NMVOC+CO over foreign regions (0.4-0.6 ppb for 20% reductions)

More info at www.htap.org, 2007 TF HTAP Interim Report

TF HTAP multi-model publications: Shindell et al., ACP, 2008: Transport to the ArcticSanderson et al., GRL, 2008: NOy transportFiore et al., JGR, in press: Surface O3Reidmiller et al., in prep: U.S. surface O3 Jonson et al., in prep: Evaluation with O3 sondesCasper et al., in prep: Health impacts (O3) Schultz et al., in prep: Idealized tracers

Some Remaining Questions.. And much more TF HTAP work ongoing to inform 2010 report!What is the contribution of hemispheric transport to metrics relevant to attainment of O3 air quality standards?

How important is interannual variability?

What is causing model spread? Can we tie to specific processes and use observational constraints to reduce uncertainty?

Can we scale O3 responses to other combinations and magnitudes of emission changes?

How will climate change affect hemispheric transport of air pollution?

Wide model range in AQ-relevant metrics: MAM average daily max 8-hour (MDA8) surface O3 over the USA (HTAP models)ppb

CASTNet sites used in model evaluationReidmiller, AGU, 2008; in prep for JGR

Model EvaluationCorrelations are generally strongest in East & weaker in WestModels have large (+) biases in summer that are largest in the EastWide spread in individual models, but ensemble represents obs quite wellReidmiller, AGU, 2008; in prep for JGR

10-model mean response of MDA8 ozone to 20% reductions of foreign emissions: MAM averageEnsemble mean MDA8 O3 decrease from -20% EA + EU + SA anthrop. emissionsVariability in response to foreign emissions? e.g., clean vs. polluted conditions?Ensemble mean base case MDA8 O3Ensemble mean MDA8 O3 decrease from -20% NA anthrop. emissionsppbppbppb(Models regridded to common 2x2.5 grid)

MDA8 O3 response to 20% emissions reductions: 3 foreign regions vs. North America regionResponse to foreign emissions greatest in springFor most regions O3 response (to -20% foreign emissions ) is ~0.5 ppbv in springResponse to domestic emissions greatest in summer at high end of O3 distributionFor all regions, response to domestic emissions greater than to foreign emissions (~2-10x; varies with season) Reidmiller, AGU, 2008; in prep for JGR

Some Remaining QuestionsWhat is the contribution of hemispheric transport to metrics relevant to attainment of O3 air quality standards?

How important is interannual variability?

What is causing model spread? Can we tie to specific processes and use observational constraints to reduce uncertainty?

Can we scale O3 responses to other combinations and magnitudes of emission changes?

How will climate change affect hemispheric transport of air pollution?

Image from http://www.cpc.noaa.gov/products/precip/CWlink/pna/nao.timeseries.gifMOZART2 simulations GMI simulations GMI simulations http://jisao.washington.edu/data_sets/pna/MOZART runs

Inter-model spread generally larger than that due to interannual variability in meteorology

Some Remaining QuestionsWhat is the contribution of hemispheric transport to metrics relevant to attainment of O3 air quality standards?

How important is interannual variability?

What is causing model spread? Can we tie to specific processes and use observational constraints to reduce uncertainty?

Can we scale O3 responses to other combinations and magnitudes of emission changes?

How will climate change affect hemispheric transport of air pollution?

A measure of uncertainty in SR relationships (sfc o3): Model spread can be > factor of 2Comparison with surface obs showsno relationship btw base-case bias and source-receptor relationship (e.g., NA->EU)Models do not alwaysrank in consistent way!Multi-model mean

Individual models sometimes rank consistently in terms of source region influence on multiple receptorsPossible explanations:

-- Emissions (not major player: similar across models, except EU NMVOC)

-- Export / transport / mixing processes

-- Chemistry Individual model

Idealized tracer experiments (CO tagged by region; all models use same emissions) suggest some role for vertical mixing in source region Less vertical mixingMore vertical mixingIndex adapted from Martin SchultzSpringtime (MAM) r2 = 0.56Surface O3 decrease over EU from -20% NA emis.(SR1-SR6NA; ppb)Ratio of NA CO tracer burden at 3-8km to 0-2km over NAIndividual modelEXAMPLE for NA EU surface ozone

FiresLandbiosphereHumanactivity Continent 1Models likely differ in export of O3 + precursors, downwind chemistry, and transport to receptor regionOcean Ocean O3NOyNOy partitioning (e.g., PAN vs. HNO3) influences O3 formation potential far from source regionNOxPANO3 otherorganic nitrates HNO3N2O5O3

PAN transport can lead to highly efficient O3 production downwindHudman et al., JGR, 2004Emmerson & Evans, ACPD, 2008: significant variations in the calculated concentration of PAN between the schemes [model chemical mechanisms] Does surface O3 response to emission changes in foreign regions correlate with: -- O3 response over source region? Yes EU (r2=0.3-0.5); NO in other regions (r2

Change in PAN over upwind region (or receptor) correlates with surface ozone change over receptor region Separation of lowest sensitivity models and higherChange in PAN burden (trop column) over upwind region in spring (Tg)Surface o3 decrease over receptor region (ppb)Individual modelEANA O3 vs. N. Pacific PAN: r2 = 0.36NAEU O3 vs. N. Atlantic PAN: r2 = 0.36Individual model

What observations would help discriminate among models (and reduce uncertainties in O3 response to foreign emission changes)? Simulated O3 response not correlated with total ozone or ozone bias w.r.t. obs.

Potential for PAN measurements to help reduce uncertainty? 2001 Observations: TRACE-P (Asian outflow), PHOBEA (inflow to N. America)

What causes the 1 ppb spread across models in surface ozone response to -20% global [CH4]? Full range of 18 models Annual mean surface O3 decrease (ppb )EU NA E Asia S Asia Strong correlations for all regions:EA vs. EU r2 = 0.75SA vs. EA r2 = 0.83NA vs. SA r2 = 0.86

Some models more responsive to [CH4] changes

Surface O3 decrease over EU vs. NA (ppb) r2 = 0.88Individual model

Differences in lifetime against tropospheric OH are a strong contributor to model spread in O3 response to CH4 Surface O3 decrease (ppb) over NA from -20% [CH4] Normalizing by CH4 lifetime reduces inter-model range from 1 to 0.5 ppb (similar in other receptor regions)

Total atmospheric methane lifetime

HTAP Event Simulations: Moving towards process-based evaluationfrom Isabelle Beys presentation at DC June 2008 HTAP meetingclean lower trop.biomass burning influenced air massesmiddle-upper troposphere polluted lower trop.observationsmodelPreliminary results from the French model MOCAGE, courtesy of N. Bousserez and J.-L- Atti, Laboratoire darologie Toulouse, France I. Bey, M. Evans, K. Law, R. Park, E. Real, S. Turquety1. chemical signatures of air masses, 2. chemical evolution in background vs. polluted plume ensembles, 3. export efficiencies, 4. injection heights on biomass burning plumes

Some Remaining QuestionsWhat is the contribution of hemispheric transport to metrics relevant to attainment of O3 air quality standards?

How important is interannual variability?

What is causing model spread? Can we tie to specific processes and use observational constraints to reduce uncertainty?

Can we scale O3 responses to other combinations and magnitudes of emission changes?

How will climate change affect hemispheric transport of air pollution?

Wu et al., submitted to GRLIntercontinental O3 response to changes in NMVOC emissions scales linearly; not so for NOx (except summer)O3 response to -20% vs. -100% EU emissions: NOx vs. NMVOC in spring(GMI model)Change of scale(5x gives same height bars) Relative benefit of decreasing NOx vs. NMVOC emissions increases with the magnitude of emission reductionsReceptor regionsReceptor regions

Some Remaining QuestionsWhat is the contribution of hemispheric transport to metrics relevant to attainment of O3 air quality standards?

How important is interannual variability?

What is causing model spread? Can we tie to specific processes and use observational constraints to reduce uncertainty?

Can we scale O3 responses to other combinations and magnitudes of emission changes?

How will climate change affect hemispheric transport of air pollution?1/16/09 update on future climate HTAP simulations:The RCP process is expected to publish scenarios in the February/March timeframe. Given the central role that these scenarios are likely to play in the science and policy processes over the next several years, we believe that it is worth waiting to make some final decisions until this work is completed. Terry Keating (US EPA) and Andre Zuber (EC), co-chairs of TF HTAP

Conclusions: Hemispheric Transport of O3

Benchmark for future: Robust estimates + key areas of uncertainty

Import Sensitivities (D O3 from anthrop. emis. in the 3 foreign vs. domestic regions): 0.5-1.1 during month of max response to foreign emis; 0.2-0.3 during month of max response to domestic emissions

Comparable O3 decrease from reducing equivalent % of CH4 and NOx+NMVOC+CO over foreign regions (0.4-0.6 ppb for 20% reductions)

Variability of O3 response within large HTAP regions; U.S. example -- multi-model mean captures much of day-to-day variability

Inter-model differences >> year-to-year variability

Different model responses seem partially due to vertical mixing, PAN -- potential for PAN measurements to help constrain O3 response?

Non-linearity in O3 response to foreign NOx emissions impacts relative benefit of NOx vs. NMVOC emission controls

More info at www.htap.org, 2007 TF HTAP Interim Report, Fiore et al., JGR, in press

****2 example S-R pairs***Springtime: 10 models equivalent; 4 EA 30-55% > EU; annual mean that is 8 predict equivalent & 6 suggest 25-50% greater from EA

**Conclude that response to foreign, although 10ths of ppb is not trivial when compared with response to equivalent % reductions in domestic anthrop. Emissions Point out shoulder = high-transport seasons, where future growth in foreign emissions may extend season of poor air quality*Mention: SA emis smallest in annual mean / springtime; EA spring, most models EU/NA > SA; SA: many models annual mean equivalent responses to at least 2 regions*20% global CH4 -25% global anthrop. Emissions (accounting for feedback of methane on its own lifetime (F = 1.33)+ anthrop = 60% total CH4 emissions [IPCC 2007])********CORRELATE WITH PAN!Index = measure of exchange btw pbl & free tropNote: found little correlation with NAEU surface ozone and NA NOx emissions (in general NOx emissions dont differ by much across the models, so model spread seems to be more driven by chemistry/transport)

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