1. Aircraft GC 2006 ems GC Streets ems East Asian contrib Lightning contrib Aircraft GC 2006 ems GC Streets ems No Asian No Lightning Long-range transport of NO y and O 3 during INTEX-B: satellite, aircraft, and model perspectives Thomas W. Walker 1 (thomas.walker@dal.ca), Randall V. Martin 1,2, Richard Leaitch 3, Anne Marie Macdonald 3, Kurt Anlauf 3, Jerry R. Ziemke 4, Ronald C. Cohen 5, Melody Avery 6, Andrew Weinheimer 7 1 Dalhousie University 2 Harvard-Smithsonian Centre for Astrophysics, 3 Environment Canada 4 NASA GSFC 5 UC Berkeley 6 NASA LaRC 7 NCAR SUMMARY We interpret the INTEX-B aircraft data from the Canadian Cessna, C-130, and DC-8 in the context of model results and Ozone Monitoring Instrument (OMI) products. We use a chemical transport model (GEOS-Chem) to examine the relationship between East Asian NO x emissions and ozone columns in over the Pacific. We also use the CTM to decompose the ozone column over the Pacific into its sources. Our GEOS-Chem simulation generally performs well against the satellite and aircraft data sets, capturing much of the geographic and vertical structure. The model does exhibit a 5 ppb bias in the ozone profiles compared to the aircraft data. Using the model, we attribute at least 4-10 Dobson Units (DU) of the Pacific tropospheric ozone columns to lightning NO x emissions, and at least 4-10 DU to Asian anthropogenic NO x emissions. Lightning contributes more to the ozone and NO y budgets at high altitudes, while anthropogenic sources are more significant near the surface. METHOD OPEN ISSUES CONCLUSIONS RESULTS Aircraft ozone: The GEOS-Chem simulation using the Streets inventory captures the relative shape of the vertical profile, but exhibits a 5-10ppb bias compared with campaign averages for all three platforms. Using the scaled 2006 emissions reduces the bias by 1-2ppb. Below 400hPa, the contribution from East Asian emissions exceeds that due to lightning. All aircraft data were filtered to exclude city plume and stratospheric influences. Error bars represent one standard deviation of the measurements at each altitude level. Aircraft NO y : Again, the simulation captures the shape of the NO y campaign average vertical profiles, but errs slightly in magnitude. East Asian and lightning sources contribute between 10-50% of the NO y seen by the DC-8. Scaled 2006 emissions: We begin with 2000 East Asian anthropogenic NO x emissions from Streets et al [2003] and scale forward to 2003 using factors derived from fossil fuel tallies (CDIAC). We then use the ratio of 2003 and 2006 SCIAMACHY tropospheric NO 2 columns to scale up to 2006. The scaling results in a 28% increase in total anthropogenic emissions over the region. Also, the mid-latitude lightning source is increased to 1.6 Tg N a -1, according to ICARTT constraints (Hudman et al [2007]). For comparison with aircraft, the model was sampled concurrently along the flight tracks. Each simulation used an 8-month spinup. Source attribution: We run the GEOS-Chem CTM without anthropogenic Asian emissions to infer the anthropogenic contribution from Asia. Likewise, we run the model without lightning NOx source. Why is the ozone simulations in the Pacific low compared to observations? Overestimate of NO y remaining in aged airmasses Missing/underrepresented deposition? Satellite-based inversion of NO x emissions based on OMI NO 2 retrieval should improve our estimate of East Asian anthropogenic emissions For tropospheric ozone columns over the Pacific, we can attribute: At least 4-10 DU to East Asian NO x emissions At least 4-10 DU to lightning NO x emissions Our simulation captures correct shape of vertical profiles compared to INTEX-B aircraft data Scaling East Asian anthropogenic NO x emissions forward to 2006 does diminish the model bias relative to satellite and aircraft measurements East Asian contribution to ozone and NO y observed by aircraft is 10-50%, comparable to the contribution from lightning Satellite comparison: Simulation results (average over April-May 2006) with 2006 NO x emissions underestimate Pacific ozone columns relative to tropospheric OMI column observations, as obtained by Ziemke et al [2006]. The simulation does capture the pollution plume that originates in East Asia Source attribution: At the western coast of North America, both East Asian emissions and lightning contribute at least 4-6 DU to the tropospheric ozone columns. The lightning contribution increases towards the tropics, while the Asian contribution increases to the west. These estimates represent lower bounds due to ozone production non- linearity. INTEX-B Science Meeting Virginia Beach, VA March 6-8, 2007 Streets et al. An inventory of gaseous and primary aerosol emissions in Asia in the year 2000. JGR, 2003 Hudman et al. Surface and lightning sources of nitrogen oxides over the United States: magnitudes, chemical evolution, and outflow. JGR, in press, 2007 Ziemke et al. Tropospheric ozone determined from Aura OMI and MLS: Evaluation of measurements and comparison with the Global Modelling Initiative's Chemical Transport Model. JGR, 2006 This work was supported by the National Science and Engineering Research Council Special Research Opportunity program. ACKNOWLEDGEMENT REFERENCES Geographic structure DC-8 measurements averaged in the vertical between 400-800 hPa (top panel) tend to be higher than those points sampled concurrently along the flight paths in GEOS-Chem (2006 emissions; bottom panel). Some of the relative variation is captured.