INTERCONTINENTAL AND HEMISPHERIC POLLUTION Daniel J. Jacob Harvard University

PART 1: THE NORTHERN MID-LATITUDES POLLUTION BELT

SPATIAL SCALES OF AIR POLLUTION: A HISTORICAL PERSPECTIVE Urban (pre-1970s) Regional (1970s) acid rain haze ozone smog Intercontinental (2000s) ozone, PM Mercury, POPs Greenhouse and aerosol-driven climate change (1980s) Stratospheric ozone depletion (1970s) SOURCE CONTINENTRECEPTOR CONTINENT OCEAN

PART I: THE NORTHERN MID-LATITUDES POLLUTION BELT

THREE POLES OF ANTHROPOGENIC EMISSIONS: NORTH AMERICA, EUROPE, EAST ASIA 10 9 atoms N cm -2 s -1 Anthropogenic 2000 NO x emissions [IPCC, 2001] 20 o 60 o 40 o …define a northern midlatitudes pollution belt Population (billons) NO x (Tg N yr -1 ) SO x (Tg S yr -1 ) Asia (A2) 2020 (B2) OECD (A2) 2020 (B2) IPCC 2020 projections (IMAGES model)

LARGE EPISODIC SOURCES FROM DUST AND FIRES Annual mean 2001 dust emissions [Fairlie et al., 1004] …desertification could increase source Annual mean fire emission climatology [Duncan et al., 2003] …climate warming, legacy of fire suppression could increase boreal forest fires

VERTICAL STRUCTURE OF THE ATMOSPHERE Tropopause Stratopause Stratosphere Troposphere Ozone layer Mesosphere Troposphere: 85% of atmospheric mass Stratosphere: 15% Mesosphere and above: less than 0.1% Tropopause is at 8-18 km altitude depending on latitude and season

GLOBAL ATMOSPHERIC TRANSPORT: THE HADLEY CIRCULATION (1735) HOT COLD Explains: Intertropical Convergence Zone (ITCZ) with strong separation of northern and southern hemispheres Stronger winds in winter than in summer Problem: does not account for Coriolis force. Meridional transport of air between Equator and poles would result in unstable longitudinal motion.

TROPICAL HADLEY CELL Easterly “trade winds” in the tropics at low altitudes Westerlies at high altitudes Subtropical anticyclones at about 30 o latitude Coriolis force in northern hemisphere pushes air to R of direction of motion; Hadley circulation initiated at Equator extends only to ~30 o latitude

CLIMATOLOGICAL SURFACE WINDS AND PRESSURES (January) storm track

CLIMATOLOGICAL SURFACE WINDS AND PRESSURES (July)

500 hPa (~6 km) CLIMATOLOGICAL WINDS IN JANUARY: strong mid-latitude westerlies

500 hPa (~5 km) CLIMATOLOGICAL WINDS IN JULY mid-latitude westerlies are weaker in summer than winter

TYPICAL TIME SCALES FOR HORIZONTAL TRANSPORT 1 week 1-2 months 1 year

LIFTING AND SUBSIDENCE Warm, wet or converging (low-pressure) area- SMALL SCALE Initial lifting H 2 O condensation heats rising air, accelerates lifting (buoyancy) 1-3 km BOUNDARY LAYER FREE TROPOSPHERE Stable layer caps cloud Outflow air cools and sinks - LARGE SCALE SUBSIDENCE INVERSION as air subsides it warms by compression slow entrainment In boundary layer

CONTINENTAL VENTILATION AND INTERCONTINENTAL TRANSPORT CONTINENTAL BOUNDARY LAYER mixing ~ 1 day 1-3 km Source continent Ocean weak winds Fast removal of ozone, PM (deposition, chemistry) FREE TROPOSPHERE Receptor continent fronts convection every ~ 5 days strong winds slow removal of ozone, PM Subsidence mixing ~ 1 day rain; scavenging of PM Tropopause (8-18 km) mixing ~ weeks STRATOSPHERE Background

INTERCONTINENTAL TRANSPORT BETWEEN NORTHERN MIDLATITUDE CONTINENTS AsiaN. America Europe Boundary layer Free troposphere liftingsubsidence boundary layer advection Tropopause HEMISPHERIC POLLUTION BACKGROUND “Direct” intercontinental transport Mixing Direct intercontinental transport: fast (~1 week) transport from source to receptor continent; either by boundary layer advection or by lifting to lower free troposphere followed by subsidence Hemispheric pollution: pollution mixes in free troposphere, affecting free tropospheric background, in turn affecting surface concentrations by subsidence 2 km

ILLUSTRATION: GLOBAL TRANSPORT OF CARBON MONOXIDE (CO) Sources of CO: Incomplete combustion (fossil fuel, biofuel, biomass burning), oxidation of VOCs Sink of CO: atmospheric oxidation by OH radical (lifetime ~ 2 months) MOPITT satellite observations of CO concentrations at 500 hPa (~6 km)

SIMULATION OF CO TRANSPORT WITH GEOS-CHEM GLOBAL 3-D MODEL OF ATMOSPHERIC TRANSPORT AND CHEMISTRY Model developed by Harvard Atmospheric Chemistry Modeling Group, presently used by 16 research groups in North America and Europe; documented in ~70 research publications. 3-d grid structure Driven by assimilated meteorological data (“real winds”) from NASA Global Modeling and Assimilation Office (GMAO) Applied to a wide range of global and regional atmospheric problems involving ozone, PM, greenhouse gases, etc. Includes coupled ozone-PM-Hg simulation capability nested with EPA CMAQ regional model Most results presented today use a horizontal resolution of 2 o x2.5 o (~200 km); some use 1 o x1 o or 4 o x5 o

PART 1 (TRANSPORT): IMPORTANT POINTS N. America, Europe, and Asia define a “northern mid-latitudes pollution belt” with fast westerlies driving circumpolar transport on time scale of a few weeks Lifting out of the continental boundary layer by convection and fronts is important for the intercontinental transport of ozone and PM (faster winds, longer lifetimes) This lifting and subsequent mixing in the free troposphere produces a “hemispheric pollution background” that contributes to surface pollution by subsidence. For ozone at least, this hemispheric pollution is more important than direct intercontinental transport

PART 2: OZONE

ENVIRONMENTAL IMPACTS OF ATMOSPHERIC OZONE NO x = NO + NO 2 : nitrogen oxide radicals VOC (volatile organic compounds) = light hydrocarbons and substituted organic compounds UV shield Greenhouse gas Primary source of OH radicals Smog

HEMISPHERIC OZONE POLLUTION: IMPLICATIONS OF ENHANCED BACKGROUND FOR MEETING AIR QUALITY STANDARDS (AQS) ppbv Europe AQS (seasonal) U.S. AQS (8-h avg.) U.S. AQS (1-h avg.) Preindustrial ozone background Present-day ozone background at northern midlatitudes Europe AQS (8-h avg.)

QUANTIFYING THE OZONE BACKGROUND BY CORRELATION WITH POLLUTION TRACERS Summer afternoon data at eastern U.S. sites [Trainer et al., 1993] Alternatives are to use back-trajectories, remote upwind sites; all Indicate background ozone concentrations in surface air of ppbv [Altshuller and Lefohn, 1996]

OCCURRENCES OF VERY LOW OZONE (< 10 ppbv) AT U.S./EUROPEAN CONTINENTAL SITES REFLECT LOCAL DEPLETION, NOT BACKGROUND Harvard Forest, Massachusetts [Munger et al., 1996] Local depletion is due to: deposition (esp. at night when surface atmosphere is stratified) chemical titration in fresh pollution plumes (esp. in winter)

GLOBAL MODEL BUDGET OF TROPOSPHERIC OZONE O3O3 O2O2 h O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CO, VOC NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km Chem prod in troposphere Chem loss in troposphere Transport from stratosphere 390 Deposition Tg O 3 yr -1 present natural NO x, CO, methane, nonmethane VOC (NMVOC) emissions Ozone lifetime: ~1 wk in boundary layer ~1 mo in free troposphere Inventory (Tg): [Mickley et al., 1999] Limiting ozone precursors: NO x and methane

SENSITIVITY OF GLOBAL TROPOSPHERIC OZONE INVENTORY (Tg) TO 50% GLOBAL REDUCTIONS IN ANTHROPOGENIC EMISSIONS GEOS-CHEM model [Fiore et al., [2002] NO x and methane have the greatest impacts

RISING METHANE OVER 20 th CENTURY Historical methane trend Recent methane trend The rise in methane over the 20 th century accounts for about 50% of the concurrent rise in global tropospheric ozone according to models Present-day sources (Tg yr -1 ) [IPCC, 2001]: Natural: wetlands (180), termites (25), biomass burning (20) Anthropogenic: livestock (90), rice (85), natural gas (60), landfills (50), coal (40) Sink: oxidation by OH (lifetime 10 years)

NO x EMISSIONS (Tg N yr -1 ) FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2 Limiting precursor for ozone production both regionally (smog) and globally

TROPOSPHERIC NO 2 FROM THE GOME SATELLITE INSTRUMENT (July 1996) Martin et al. [2002] Maps the distribution of surface NO x emissions and has so far largely confirmed the validity of emission inventories

NONLINEAR DEPENDENCE OF OZONE PRODUCTION ON NO x IS RESPONSIBLE FOR (1) HIGH OZONE BACKGROUND, (2) DAMPED SENSITIVITY TO NO x EMISSION REDUCTIONS NO x Ozone production efficiency (OPE): number of ozone molecules produced per molecule of NO x consumed Nitric acid (HNO 3 ) Peroxyacetylnitrate (PAN) CONTINENTAL BOUNDARY LAYER High NO x :  OPE ~5-10 FREE TROPOSPHERE fronts convection PAN NO x HNO 3 Lightning Low NO x :  OPE ~ NO x lifetime ~ hours 10-20% of emitted NO x is exported, mainly as PAN O3O3 O3O3 1-3 km

BACKGROUND OZONE CONCENTRATIONS INCREASE WITH ALTITUDE stratosphere Latitude over NW Pacific Longitude China coast California coast [Browell et al., 2003] Mean aircraft lidar observations over N Pacific (spring 2001) …because of long lifetime, high-altitude production, transport from stratosphere

Climatology of observed ozone at 400 hPa (7 km altitude) in July from ozonesondes and MOZAIC aircraft GEOS-CHEM model tropospheric ozone columns for July NORTHERN HEMISPHERIC ENHANCEMENT OF OZONE Li et al. [2001]

LATE SPRING MAXIMUM OF OZONE BACKGROUND AT NORTHERN MID-LATITUDES The origin of this spring maximum is complicated and reflects contributions from photochemical production relatively long lifetime (thick stratospheric ozone column) efficient lifting and fast westerly transport maximum in stratospheric influence Naja et al. [2003] 3-5 km 0-3 km marine sites

MONTHLY MEAN AFTERNOON OZONE CONCENTRATIONS AT NON-URBAN U.S. SITES (CASTNet NETWORK) IN Natural ozone: ppbv Hemispheric pollution enhancement: 5-15 ppbv, highest in spring * Observations Background (no anthrop. emissions in N. America, present methane) Natural (no anthrop. emissions globally, preindustrial methane) Model: Base (2001) Stratospheric influence Fiore et al. [2002]

TRANSATLANTIC TRANSPORT OF N. AMERICAN OZONE (GEOS-CHEM model results for 1997) Li et al. [2002] APRIL JULY L H H L Iillustrates the stronger intercontinental influence in spring Mace Head site

OZONE DATA AT MACE HEAD, IRELAND (MAR-AUG 1997) Observed [Simmonds] GEOS-CHEM model N.America pollution events in model Li et al. [2002] Intercontinental pollution influence in surface air is not detectable from observations alone

QUANTIFYING INTERCONTINENTAL POLLUTION INFLUENCE REQUIRES MODEL SIMULATIONS WITH MODIFIED EMISSIONS Calculating a partial derivative of ozone relative to NO x emisions and extrapolating [Wild and Akimoto, 2001] iis unsatisfactory because of nonlinearity Tagging model ozone by its location of origin (e.g., ozone produced over North America and transported to Europe) [Derwent et al., 2003] is unsatisfactory both because of nonlinearity and because it does not separate natural from anthropogenic production Statistics of observed ozone enhancements when trajectories point to an upwind continental origin [Weiss-Pezias et al., 2004] are unsatisfactory because of confounding effects from latitudinal and vertical gradients in background ozone Observations of intercontinental transport of pollution plumes in the free troposphere [Stohl and Trickl, 1999] are not necessarily relevant to enhancements in surface air

MEAN SURFACE OZONE ENHANCEMENTS FROM ANTHROPOGENIC NO x AND NMVOC EMISSIONS BY DIFFERENT CONTINENTS GEOS-CHEM model, July 1997 North America Europe Asia Li et al. [2002] as determined from sensitivity simulations with these sources shut off

FORECASTING TRANSATLANTIC TRANSPORT OF NORTH AMERICAN POLLUTION TO EUROPE WITH THE NORTH ATLANTIC OSCILLATION (NAO) INDEX NAO Index North American ozone pollution enhancement At Mace Head, Ireland (GEOS-CHEM model) r = 0.57 NAO index = normalized surface P anomaly between Iceland and Azores Li et al. [2001] Greenhouse warming  NAO index shift  change in transatlantic transport of pollution

Fiore et al. [2001] and Li et al. [2002] tropical air Subsidence of Asian pollution + local production stagnation RANGE OF INTERCONTINENTAL OZONE POLLUTION ENHANCEMENTS AT SURFACE SITES (GEOS-CHEM model) over U.S. over Europe variability is small effect is maximum for ozone concentrations in mid-range (40-70 ppbv)

EFFECT OF NORTH AMERICAN SOURCES ON EXCEEDANCES OF EUROPEAN AIR QUALITY STANDARD (55 ppbv, 8-h average) GEOS-CHEM model results, summer 1997 Number of exceedance days (out of 92) # of exceedance days that would not have been in absence of N.American emissions Li et al. [2002]

OZONE POLLUTION ENHANCEMENTS ARE LARGER IN FREE TROPOSPHERE THAN AT SURFACE Mean GEOS-CHEM ozone enhancements at 45 o N in summer from anthropogenic emissions of NO x and NMVOCs in different continents N America EuropeAsia N. American emissions European emissions Asian emissions Li et al. [2002]

NOAA/ITCT-2K2 AIRCRAFT CAMPAIGN IN APRIL-MAY 2002 Monterey, CA High-ozone Asian pollution plumes observed in lower free troposphere but not at surface (Trinidad Head) CO O3O3 PAN HNO 3 May 5 plume at 6 km: High CO and PAN, no O 3 enhancement May 17 subsiding plume at 2.5 km: High CO and O 3, PAN  NO x  HNO 3 Hudman et al. [2004] Observations by D. Parrish, J. Roberts, T. Ryerson (NOAA/AL)

CONCEPTUAL PICTURE OF OZONE PRODUCTION IN TRANSPACIFIC ASIAN POLLUTION PLUMES NO x HNO 3 PAN Asian boundary layer (OPE ~ 5) PAN, weak  O 3 Warm conveyor belt; 5-10% export of NO y mainly as PAN strong  O 3 Subsidence Over E Pacific OPE PAN  NO x  HNO 3 U.S. boundary layer very weak  O 3 10x dilution (Asian dust data) E. Asia Pacific United States Hudman et al. [2004] Stratospheric downwelling GEOS-CHEM

CALIFORNIA MOUNTAIN SITES ARE PARTICULARLY SENSITIVE TO ASIAN OZONE POLLUTION …because there is no dilution in the boundary layer Observed 8-h ozone at Sequoia National Park (1800 m) in May 2002 vs. corresponding simulated (GEOS-CHEM) Asian pollution ozone enhancement Asian enhancements are 6-10 ppbv during NAAQS exceedances; unlike at surface sites, Asian pollution influence is not minimum under high-ozone conditions! May 17 obs. Asian plume event in red Hudman et al. [2004]

IPCC [2001] PROJECTION OF FUTURE METHANE EMISSIONS Methane is the second most important anthropogenic greenouse gas after CO 2 …and also a limiting precursor for global production of tropospheric ozone

Combined effects of future anthropogenic emission trends on U.S. ozone air quality and on global climate 50% NMVOC 1995 (base ) 50% CH 4 50% NO x 2030 A B1 50% NMVOC 50% CH 4 50% NO x 2030 A B1 IPCC scenario Fossil fuel NO x emissions (2020 vs. present) Global U.S. Methane concentration (2020 vs. present) A1+80%-30%+35% B1+10%-60%+20% GEOS-CHEM model simulations [Fiore et al.,2002] Ozone pollution

LENGTHENING OF OZONE POLLUTION SEASON IN UNITED STATES IN 2030 A1 SCENARIO 2030 A Base Case Fiore et al. [2002] Rising background from methane and Asian NO x emissions has most effect In spring Fiore et al. [2002]

INCREASE IN FREE TROPOSPHERIC BACKGROUND OZONE OVER EUROPE IN THE PAST CENTURY Observations at mountain sites [Marenco et al., 1994] Preindustrial model ranges Are natural ozone sources (esp. lightning NO x ) overestimated in models? …but the old observations also have uncertain calibrations

TREND IN BACKGROUND OZONE IN EUROPE Hohenpeissenberg and Payerne data NO x emission trends 3-5 km km polluted background Increase until the mid-1980s and then leveling off; would seem consistent with emission trends Naja et al. [2003]

TRENDS IN OZONESONDE DATA AT NORTHERN MID-LATITUDES, observed GEOS-CHEM model Some indication of positive trend but models cannot reproduce contrast between N. America vs. Europe and Asia seasonal variation in the trend Fusco and Logan [2003]

8-h daily maximum ozone frequency distribution at rural U.S. sites [Lin et al., 2000] BACKGROUND OZONE IN SURFACE AIR OVER U.S. APPEARS TO HAVE INCREASED BY ~3 ppbv OVER THE PAST 20 YEARS This increase in background and compression of the frequency distribution has also been observed in Switzerland [Bronnimann et al., 2002] and is consistent with models [Fiore et al., 2002]

OBSERVED TREND IN OZONE BACKGROUND OVER CALIFORNIA IN SPRING SUGGESTS ppbv INCREASE OVER PAST 20 YEARS Trend: ppbv yr -1 Jaffe et al. [2003] Such a large increase is not consistent with models

EFFECT OF INCREASING SIBERIAN FOREST FIRES ON SUMMER SURFACE OZONE IN PACIFIC NORTHWEST Mean summer 2003 enhancement of 5-9 ppbv (9-17 ppbv in events) Jaffe et al. [2004] Observations GEOS-CHEM ozone enhancements Siberian fires CO Ozone

BACKGROUND OZONE IS NOT ONLY IMPORTANT FOR EXCEEDANCE OF AIR QUALITY STANDARDS, IT IS ALSO IMPORTANT FOR SETTING THE STANDARDS Environmental risk Pollutant concentration BackgroundAQS Acceptable added risk EPA defines as “Policy-Relevant Background” those concentrations that would be present in the absence of North American)anthropogenic emissions: presently 40 ppbv is assumed

Lefohn et al. [2001] challenge to 84 ppbv NAAQS …under current revision presently used by EPA (under review) O 3 (ppbv) Bacgkround range considered by EPA in last revision of ozone standard 84 ppbv: current NAAQS Frequent observations at remote U.S. sites attributed to natural background [Lefohn et al., “Present-day Variability of background ozone in the lower troposphere”, Journal of Geophysical Research, 106, , 2001]

Ozone time series at CASTNet stations used by Lefohn et al. [2001] CASTNet sites Model Background Natural O 3 level Stratospheric + * Hemispheric pollution Regional pollution }  } Model reproduces structure; regional pollution is #1 factor, hemispheric pollution also significant. Natural background has little variability Fiore et al., JGR pm daily data

Daily afternoon (1-5 p.m.) surface ozone March-October 2001 Background ppbv; Natural ppbv; Stratosphere < 20 ppbv Probability ppbv -1 Typical ozone values in U.S. surface air: Compiling model results from all CASTNet sites… Observations at CASTNet sites Model (base) Stratospheric Natural Background

DEPLETION OF OZONE BACKGROUND DURING REGIONAL POLLUTION EPISODES Background (clean conditions) O 3 vs. (NO y -NO x ) At Harvard Forest, Massachusetts Background (pollution episodes) Observed (J.W. Munger) model (GEOS-CHEM) model background Pollution coordinate Fiore et al. [2002]

Cumulative probability distributions for daily mean afternoon O 3 at CASTNET sites, spring-summer 2001 CASTNet sites Model Background Natural O 3 level Stratospheric + * Fiore et al., JGR 2003 Apr-MayJul-Aug 11 remote sites (western U.S.) 34 polluted sites (eastern U.S.) An improved specification of the “policy-relevant ozone background” should recognize decrease from spring to summer and under polluted conditions; background should in any case be lower than 40 ppbv, Implying that current NAAQS is too lax Regional pollution

PART 2 (OZONE): SUMMARY The natural ozone concentration in surface air over northern mid- latitudes continents is ppbv with little variability according to models; observations suggest that it could be even lower. The present-day background ozone concentration in surface air over norhern mid-latitudes continents (zeroing anthropogenic emissions from that continent) is ppbv according to both models and observations. Observed trends in background over the past decades are inconsistent, and the ability of models to reproduce them is unclear. Simulated mean surface ozone enhancements from anthropogenic NO x and NMVOC emissions in other continents are typically 2-5 ppbv, highest when ozone concentrations are in midrange (40-70 ppbv). Anthropogenic methane adds another 4- 6 ppbv enhancement to surface ozone according to models. Background influence is typically low under regional pollution episodes, implying that air quality standards based on risk increments above background are currently too lax.

PART 2 (OZONE): FUTURE DIRECTIONS ICARTT aircraft campaign (joint U.S-E.U., summer 2004) will observe export from North America and transatlantic transport to Europe. Satellite observations are providing ability to map emissions of NO x and NMVOCs; the TES instrument (launched on Aura this month) will provide the first global mapping of tropospheric ozone. Nested regional-global models are being developed to refine source- receptor relationships. There is continued interest in statistical analysis of ozone background and trends at remote sites; but a synthetic approach is needed. Work to better quantify methane sources has been on the back-burner over the past few years, as the climate change community is fixated on CO 2 ; interest from the air quality community would make a difference. Work to improve lightning source of NO x (currently uncertain by an order of magnitude!) is at a standstill and needs to be revived.

ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH ATLANTIC IN SUMMER 2004 SCIENTIFIC OBJECTIVES Regional Air Quality: characterize sources and transport of pollution in northeastern North America Continental Outflow: quantify North American outflow of environmentally important gases and aerosols, relate to sources Transatlantic Pollution: understand transport and chemical evolution of North American pollution across the Atlantic Aerosol Radiative Forcing: characterize direct/indirect effects of aerosols over northeastern North America and western North Atlantic International, multi-agency collaboration

ICARTT: THE PLAYERS NASA/ INTEX NOAA/ ITCT UK/ITOP DLR, CNRS Caltech/ ONR DOE/ASP MSC NSF/COBRA Zoom over northeastern North America NOAA/NEAQS

SATELLITE NEAR-REAL-TIME DATA DURING ICARTT (July 2000) AOD (July 2000) CO from MOPITT, AIRS AODs (and fires) from MODIS NO 2 from SCIAMACHY HCHO, NO 2 from GOME GOME HCHO (July 1996) Monthly means from previous years

TRANSATLANTIC LAGRANGIAN EXPERIMENT will involve coordination of NOAA, NASA, UK, DLR aircraft

NESTING REGIONAL AND GLOBAL MODELS: necessary for fine source-receptor attribution (e.g., individual countries or states) GLOBAL MODEL (GEOS-CHEM) 200 km resolution Regional model (CMAQ) 36 km 12 km 4 km Boundary conditions (“1-way nesting”) Ongoing EPA/ICAP project: C. Jang (EPA), D. Byun (UH), D. Jacob (Harvard) Has been applied by D. Byun to examine Mexican pollution influences over Texas; application to transpacific pollution influence on continental U.S. is under way Still very much in infancy; needs support from policy community Another similar effort underway in U.S. involves U. Iowa (G. Carmichael) with GFDL (Larry Horowitz)

PART 2 (OZONE): WHO IS DOING THE WORK? North America –Harvard (D. Jacob): ICARTT campaign –EPA (C. Jang) and U. Houston (D. Byun): nested regional-global modeling –Princeton/GFDL (A. Fiore): projections with future emissions –U. Washington (D. Jaffe, L. Jaegle): field studies and modeling of transpacific trasnport –NOAA/AL (D. Parrish, A. Stohl): ICARTT campaign, transport pathways Europe –U. East Anglia (S. Penkett), DLR (H. Schlager): ICARTT campaign –UK Met. Office (R. Derwent): observations and modeling of intercontinental influence on Europe –EPFL (I. Bey): global modeling of intercontinental influence on Europe –ETH (J. Staehelin): ozone trend statistics E. Asia –FRSGC (H. Akimoto): ozone trend statistics, global modeling

PART 3: AEROSOLS

DUST STORMS PROVIDE THE VISIBLE EVIDENCE OF INTERCONTINENTAL TRANSPORT! Glen Canyon, AZ Clear dayApril 16, 2001: Asian dust! Mean April 2001 PM concentrations measured by MODIS

ASIAN AND SAHARAN DUST CLOUDS CAN CAUSE EXCEEDANCES OF PM AIR QUALITY STANDARDS IN U.S. April 1998 dust event [Husar et al., 2001] Some of that dust could be anthropogenic (soil erosion)

LIFE CYCLE OF THE ATMOSPHERIC AEROSOL Soil dust Sea salt Aerosol: dispersed condensed matter suspended in a gas Size range:  m (molecular cluster) to 100  m (small raindrop) SO 2, NO x, NH 3, VOCs Most important components: -Sulfate- nitrate-ammonium -Organic carbon (OC), elemental carbon (EC) -Soil dust -Sea salt

SOURCES OF SULFATE-NITRATE-AMMONIUM AEROSOLS (2001) GLOBALUNITED STATES Sulfur, Tg S yr -1 Ammonia, Tg N yr -1 NO x, Tg N yr

SOURCES OF CARBONACEOUS AEROSOLS (1998) ORGANIC CARBON (OC) ELEMENTAL CARBON (EC) GLOBAL UNITED STATES 130 Tg yr Tg yr Tg yr Tg yr -1

ANNUAL MEAN PARTICULATE MATTER (PM) CONCENTRATIONS AT U.S. SITES, NARSTO PM Assessment, 2003 PM10 (particles < 10  m),  g m -3 PM2.5 (particles < 2.5  m),  g m -3 Red circles indicate violations of national air quality standard: 50  g m -3 for PM10 15  g m -3 for PM2.5 > < 33 > < 10

PM2.5 COMPOSITION IN THE UNITED STATES Annual means

SULFATE, NITRATE, AMMONIUM AEROSOL CONCENTRATIONS IN EUROPE Annual means [EMEP, 2003] Sulfate Nitrate Ammonium

GLOBAL AEROSOL DISTRIBUTION OBSERVED BY MODIS SATELLITE INSTRUMENT Dust and fires are larger global influences than pollution; Contrast with remote background is much stronger than for ozone because aerosols are scavenged efficiently by precipitation In contrast to ozone, direct intercontinental transport is more important than hemispheric pollution enhancement.

AIRCRAFT OBSERVATIONS IN ASIAN OUTFLOW ILLUSTRATE THE DEPLETION OF AEROSOLS DURING LIFTING TO FREE TROPOSPHERE Longitude Browell et al. [2003]

INTERCONTINENTAL TRANSPORT OF ASIAN AND NORTH AMERICAN ANTHROPOGENIC SULFATE As determined from GEOS-CHEM 2001 sensitivity simulations with these sources shut off Enhancements are insignificant for health-based air quality standards; difference with ozone reflects (1) scavenging of aerosols during export; (2) larger increment from background to standard

ASIAN POLLUTION INFLUENCES ON SULFATE, NITRATE, AMMONIUM Annual means as determined from a GEOS-CHEM 2001 sensitivity simulation with Asian anthropogenic sources shut off Sulfate Nitrate Ammonium  g m -3 Park et al. [2004]

INTERCONTINENTAL SULFATE DEPOSITION N. American and Asian anthropogenic sources each contribute 2-4% to mean sulfate deposition over Europe; mainly driven by events [Tarrason and Iversen, 1998] Intercontinental influence is weaker for surface concentrations than for deposition because of the additional dilution from subsidence

TRANSPACIFIC POLLUTION TRANSPORT EVENT Asian pollution plume sampled at Mt. Rainier, Mt. Lassen, and Crater Lake on 28 April 1993: 2.2  g m -3 ammonium sulfate 1.8  g m -3 dust 1.1  g m -3 organic carbon 0.22  g m -3 nitrate 0.16  g m -3 elemental carbon Compare to 24-h NAAQS of 85  g m -3 Jaffe et al. [2003]

INTERCONTINENTAL FIRE INFLUENCE Canadian fire plume sampled at Mace Head, Ireland [Forster et al., 2001] CO enhancements from Canadian fires Black carbon enhancement Assuming a 7/1 organic/elemental aerosol carbon mass ratio from forest fires implies a PM enhancement less than 0.8  g m -3 on Aug. 13 event – not much!

VISIB ILITY REDUCTION BY AEROSOLS Scattering by particles is most efficient when radiation wavelength = particle radius Visible light is in 0.4 – 0.7  m range, so fine aerosols (0.1-1  m) are efficient scatterers

EPA REGIONAL HAZE RULE: EPA REGIONAL HAZE RULE: Federal class I areas in the U.S. (including national parks and other large wilderness areas) must return to “natural visibility” conditions by 2064 Acadia National Park clean day moderately polluted day …will require essentially total elimination of anthropogenic aerosols!

PHASE I IMPLEMENTATION OF REGIONAL HAZE RULE State Implementation Plans (SIPs) must be submitted by 2007 for linear improvement in visibility over the period toward the 2064 natural visibility endpoint Because visibility is a logarithmic (sluggish) function of PM concentration, The phase I implementation requires ~50% reduction in emissions, highly sensitive to specification of 2064 endpoint visibility (deciviews) from EPA [2001] Anthropogenic emissions (illustrative)

“DEFAULT ESTIMATED NATURAL PM CONCENTRATIONS” FOR APPLICATION OF THE REGIONAL HAZE RULE PM mass concentration (  g m -3 ) Extinction coefficient (Mm -1 ) Intercontinental transport of pollution could prevent attainability of these natural PM targets through domestic emsision reductions only; becomes issue of “natural” vs. “background”

SURFACE PM IN EASTERN AND WESTERN U.S.: contributions from natural and transboundary pollution EPA default natural estimates are OK except for OC in west (forest fires) Transboundary pollution of SO 4 2- and NO 3 - makes natural visibility objective unachievable without international controls Transboundary sulfate pollution influence from Asia is comparable in magnitude to that from Canada + Mexico Annual regional means from GEOS-CHEM standard and sensitivity simulations (NH 4 ) 2 SO 4 (  g m -3 ) West East NH 4 NO 3 (  g m -3 ) West East OC (  g m -3 as OMC) West East Baseline (2001) Natural (no global anthrop.) Background (no U.S. anthrop.) Transboundary pollution Canada and Mexico Asia EPA default natural for RHR Park et al. [2004]

IMPLICATIONS FOR IMPLEMENTATION OF REGIONAL HAZE RULE Illustrative calculation for mean western U.S. conditions, assuming linear relationship between emissions and PM concentrations, and assuming zero trend in anthropogenic sources from foreign countries Desired trend in visibility Required % decrease of U.S. anthropogenic emissions Phase 1 30% 48% Park et al. [2004]

PART 3 (AEROSOLS): SUMMARY Export of aerosols from continents is far less efficient than for ozone because of scavenging by precipitation Intercontinental transport of pollution aerosols is negligible with regard to meeting current PM2.5 and PM10 standards; intercontinental transport of dust is of more concern Intercontinental transport is more important for acid deposition than for PM air quality standards Intercontinental pollution transport enhances sulfate concentrations several-fold relative to natural sources – important for formulation of U.S. EPA Regional Haze Rule

PART 3 (AEROSOLS): WHO IS DOING THE WORK? North America –Harvard (D. Jacob): ICARTT campaign, modeling aerosol background over U.S., MODIS data analysis –EPA/IMPROVE (W. Malm) background aerosol measurements in U.S. –NASA/GSFC (M. Chin): MODIS data analysis –U. Washington (D. Jaffe): statistical analysis of transpacific transport –NOAA/AL (A. Stohl): global transport pathways –U.C. Irvine (C. Zender): dust sources and transport Europe –U. Oslo (L. Tarrason): hemispheric modeling of intercontinental transport –ISPRA (F. Dentener): global modeling of intercontinental transport

PART 4: MERCURY

PRESENT-DAY GLOBAL BUDGET OF MERCURY (Mg yr -1 ) Anthropogenic (mostly coal): 2200 Hg 0 Hg 2 + Natural (ore): 500 Re-emission:1500 OCEAN MIXED LAYER (0-150 m) DEEP OCEAN ATMOSPHERE 5200 Atmospheric lifetime of mercury ~ 1 year SOILS 1,200,000 98%2% INVENTORIES in Mg Fluxes in Mg yr -1 11, ,000 Burial 400 Deposition Land 2200 Ocean 2000 Re-emission 2000

SHIP DATA FOR MERCURY vs. LATITUDE Weak latitudinal gradient is indicative of long lifetime Lamborg et al. [2002]

MERCURY RECORD FROM ICE CORE (WYOMING)

GEOS-CHEM SIMULATION OF ATMOSPHERIC MERCURY + …again illustrating the northern mid-latitudes pollution belt Circles indicate long-term observations

SOURCE ATTRIBUTION OF DEPOSITED MERCURY IN U.S. [Seigneur et al., 2004] “Natural” includes reemitted mercury – legacy of past century of anthropogenic emissions!