SCALE ISSUES IN MODELING INTERCONTINENTAL TRANSPORT Daniel J. Jacob, Rokjin Park, Lin Zhang, Colette L. Heald with support from NASA, EPA, EPRI Issue 4 of Background Document: “What is the effect of spatial resolution of the model on estimates of source-receptor relationships? Is it necessary to nest regional models within global models, and what difficulties must be overcome to perform this nesting? Is one way nesting sufficient, or is two-way nesting necessary?”

regional statistics and events surface stratification INTERCONTINENTAL TRASPORT AS WEDDING OF GLOBAL AND REGIONAL MODEL CULTURES GLOBAL MODELS REGIONALMODELS Priorities regional statistics and events global budgets and distributions local events Scales global (~1000 km, months) synoptic (~100 km, days) meso (~10 km, hours) Scaling nightmares boundary conditions surface stratification BL dynamics topography fine variability convection scavenging strat-trop exchange NEED TO SHARE OUR NIGHTMARES

TRANSPACIFIC TRANSPORT OF OZONE AND AEROSOLS HEMISPHERIC POLLUTION PAN VOCs (long-lived) warm conveyor belts, convection subsidence O3 OC aerosol PAN plume transport Free troposphere Sulfate OC aerosol NOx O3 2 km entrainment Boundary layer NOx, SO2, VOC aerosols, HNO3 ozone, sulfate, OC ASIA PACIFIC NORTH AMERICA

SURFACE DATA FOR OZONE AT REMOTE SITES SUGGEST LITTLE VARIANCE IN INTERCONTINENTAL INFLUENCE * CASTNet observations (13-17 LT) GEOS-Chem model Standard Background Natural Stratospheric Intercontinental ozone enhancement of 5-10 ppbv, driven by large-scale subsidence } D = Regional pollution + X } D = Intercontinental pollution Voyageurs NP, Minnesota, 2001 Fiore et al. [2003]

SURFACE OZONE AT TRINIDAD HEAD, CALIFORNIA, Apr-May 2002 Observations: 41 ± 5 ppb (filtered against local influence) GEOS-Chem model: 39 ± 5 ppb (Asian 4.5 ± 1.1 ppb) MOZART model: 37 ± 9 ppb (Asian 4.2 ± 1.3 ppb) Synoptic variability is weak in both model and observations, but local nighttime depletion (stratification) is not resolved in global models Goldstein et al. [2004]

WHY ARE INTERCONTINENTAL OZONE POLLUTION PLUMES OBSERVED IN FREE TROPOSPHERE BUT NOT AT SURFACE? Aircraft observations during NOAA/ITCT-2K2 out of Monterey (April-May 2002) Asian pollution plume at 2-4 km CO O3 May 17 This is consistent with aircraft vs. surface observations of transpacific dust plumes, which show 10x dilution between lower free troposphere and surface – but can models reproduce this? (they can’t resolve the free tropospheric plumes) Hudman et al. [2004]

but global models cannot deal properly with this INTERCONTINENTAL OZONE POLLUTION ASSESSMENTS MUST ACCOUNT FOR LOCAL TITRATION/STRATIFICATION Ozone background is depleted under stagnant/stratified/titrated conditions… but global models cannot deal properly with this CASTNet sites GEOS-Chem Model Ozone background * Ozone (ppbv) Cumulative Probability Fiore et al. [2003] Addressing this issue requires downscaling, e.g., global g regional nesting

1-WAY NESTING OF GEOS-Chem AND CMAQ: PRELIMINARY RESULTS CMAQ domain stretched from Asia to the North Atlantic April 2001 surface ozone CMAQ (GEOS-Chem boundary conditions) GEOS-Chem CMAQ and GEOS-Chem have comparable surface ozone over continents but CMAQ is lower across Pacific and transpacific pollution influence is half that in GEOS-Chem Rokjin Park (Harvard) and Carey Jang (EPA/OAQPS)

CMAQ vs. GEOS-Chem TRANSPACIFIC TRANSPORT Ozone concentrations at 25-50oN vs. pressure and longitude (April 2001) Evaluation w/ mean TRACE-P obs in Asian outflow (<140E) CMAQ Ozone, ppbv ASIA N. AMERICA GEOS-Chem TRACE-P CMAQ GEOS- Chem Low free tropospheric ozone in CMAQ likely due to processes usually neglected in regional models: STE, lightning, … Rokjin Park (Harvard) and Carey Jang (EPA/OAQPS)

Ozone-CO relationship USING SPACE-BASED TES OZONE-CO DATA TO OBSERVE INTERCONTINENTAL OZONE POLLUTION 602 hPa TES observations, July 2005 Ozone-CO relationship downwind of Asia TES R=0.64 Slope=0.62 Ozone Ozone (ppbv) ppbv GEOS-Chem Model R=0.84 Slope=0.50 Carbon monoxide (pppbv) CO ppbv Lin Zhang (Harvard)

Ozone-CO relationship downwind of eastern N. America USING SPACE-BASED TES OZONE-CO DATA TO OBSERVE INTERCONTINENTAL OZONE POLLUTION 618 hPa TES observations, July 2005 Ozone-CO relationship downwind of eastern N. America TES R=0.38 Slope=0.75 Ozone Ozone (ppbv) ppbv GEOS-Chem model R=0.79 Slope=0.67 Carbon monoxide (pppbv) CO ppbv Lin Zhang (Harvard)

TRANSPACIFIC ASIAN AEROSOL POLLUTION AS SEEN BY MODIS Heald et al. [2006] X1018 [molecules cm-2] Quantitative comparison to models must use MODIS reflectances (not AODs)

CMAQ vs. GEOS-Chem TRANSPACIFIC TRANSPORT OF SULFATE (April 2001) CMAQ GEOS-Chem Sulfate In surface air Column Asian pollution influence in U.S. surface air in CMAQ is 5x that in GEOS-Chem Rokjin Park (Harvard) and Carey Jang (EPA/OAQPS)

EVALUATING ASIAN SULFATE OUTFLOW: TRACE-P aircraft observations (Mar-Apr 2001, <140oE) Concentration, mg m-3 Altitude, km Sulfate SOx Suggests insufficient scavenging in CMAQ during venting to free troposphere Rokjin Park (Harvard) and Carey Jang (EPA/OAQPS)

TESTING TRANSPACIFIC SULFATE IN GEOS-Chem WITH SURFACE OBSERVATIONS IN NORTHWEST U.S. Model Asian sulfate Model Asian dust Observed sulfate Observed dust Model sulfate Northwest U.S. IMPROVE sites (2001) Mean Asian pollution enhancement in NW U.S. in spring: 0.16 ± 0.08 mg m-3 Heald et al. [2006]

CONCLUSIONS AND RECOMMENDATIONS Global models have capability to describe intercontinental transport on synoptic scales (100-1000 km) For policy applications, need coupling with regional models to downscale the information to meso and local scales (1-10 km) focus regional models on synoptic-to-meso downscaling 2-way nesting of course nice but 1-way nesting should be OK Apply regional models to improve simulation of continental venting requires new thinking in regional models could be exploited in 2-way nesting Improve simulation of free tropospheric pollution plumes in global models this may be tied to convective parameterizations, model resolution, advection algorithms Need to investigate model ability to describe subsidence and boundary layer entrainment