OZONE AND ITS PRECURSORS OVER THE UNITED STATES: SOURCES, OUTFLOW, TRANSPACIFIC INFLOW, AND HEMISPHERIC INFLUENCE Rynda Hudman ACCESS Friday, August 24, 2007 Good morning, my name is Rynda Hudman and I did my PhD under the supervision of Daniel Jacob in the Atmospheric Chemistry Group at Harvard University. I was funded by AMS and NSF Graduate Fellowships. I worked closely with data from three field campaigns - I cite their measurements on my slides. My thesis looked at the U.S. as a box in terms of ozone and its precursors. In particular Asian inflow, sources over the U.S. , export from the BL, and the eventual hemispheric influence of North American emissions. ACKNOWLEDGEMENTS Daniel Jacob and the Atmospheric Chemistry Modeling Group at Harvard The ITCT 2k2, PEACE A/B, and ICARTT Science Teams AMS/NOAA Office of Global Change Graduate Fellowship NSF Graduate Research Fellowship

Hemispheric Pollution Direct Intercontinental Transport Alt (km) Intercontinental Influence of Ozone (1) primary constituent of smog in surface air [NRC, 1991] (2) 3rd most important greenhouse gas [IPCC, 2001] 10 Greenhouse gas 8 hn O3 NO2 NO 6 Hemispheric Pollution 4 OH HO2 Tim gave a great introduction to ozone formation and the importance of NOx and its reservoirs. As he mentioned, in most of the atmosphere ozone production is limited by the supply of NOx. So we care about ozone, NOx and its oxidation products when discussing the influence of ozone. There are two modes of intercontinental influence. 1st Direct Intercontinental Transport of pollutants either by direct boundary layer transport or uplift into the free troposphere, transport, followed by subsidence over the receptor region. 2nd is the impact on hemispheric pollution defining a hemispheric background, pollutants are vented out of the boundary layer, mix with free tropospheric air and impact the downwind continent by subsidence. Here I examine the U.S. sources, export and hemispheric influence of ozone and its precursors as well as Asian inflow into the United States. Direct Intercontinental Transport (1 week) 2 VOCs Air quality Air quality CONTINENT 1 CONTINENT 2 OCEAN

NORTH AMERICA : at midlatitudes we are all in each others tailpipe CO column GMAO Forecast Friday, 4/20/06 - Mon, 4/24/06 CO is used as a tracer of pollution OUT IN In North America a midlatitudes we are all in each others tail pipes. Here I am showing CO My work uses aircraft measurements interpreted with a 3-D model of tropospheric chemistry to examine: Background ozone Transpacific transport Local surface production Convection/Lightning Export Transatlantic Transport

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) May 5 plume at 6 km: High CO and PAN, no O3 enhancement O3 CO PAN To study Asian inflow I looked at aircraft observations from spring 2002. First, PEACE-B which took place over Japan and the NW Pacific and ITCT2k2 which took place at the same time off shore of California. A number of Asian pollution plumes where observed in the free troposphere, but there was no visible Asian ozone plumes observed the surface site at Trinidad Head. Here I am showing two free tropospheric plumes observed by the ITCT2k2 aircraft. 1st a plume was observed on May 5th at 6km altitude off the coast of Northern California. It was of Asian fossil fuel origin (based on backward trajectories and HCs within the plume). It was uplifted by a WCB in a cyclone to ~6km and quickly transported over the Pacific. It was enhanced in CO and in PAN but there was no ozone enhancement above the local ft background. In contrast to the May 17th a plume. The plume was also uplifted in a cyclone over East Asia to ~ 6-7km altitude, mid-Pacific it the reached a weak high pressure ridge where it left the WCB and continued to slowly subside over the next 7 days to 2.5 km where it was observed offshore of Southern California. Similar to the May 5th plume it was of fossil fuel origin. It was enhanced in CO. But was depleted of PAN, total NOy was ~ the same. Comparing these plumes we fing the PAN had decomposed into NOx producing ~20 ppbv ozone in the subsiding plume. This corresponds to an ozone production efficiency per unit NOx of 53. HNO3 May 17 subsiding plume at 2.5 km: High CO and O3, PANNOxHNO3 Hudman et al. [2004] Measurements (NOAA WP-3D): T. Ryerson (O3, NOx), John Holloway (CO), Frank Flocke (PAN), Andy Neuman (HNO3)

INTERCONTINENTAL OZONE POLLUTION LAYERS ARE FREQUENTLY OBSERVED AT HIGH ALTITUDE…BUT NOT AT SURFACE Aircraft observations from ITCT-2K2 campaign out of Monterey, CA (April-May 2002); enhancements up to 40 ppbv in high-ozone layers Dilution appears to greatly dampen ozone enhancements at surface: Trinidad Head surface observations: Asian pollution enhancement in model is 6 ± 2 ppbv We can see this in the surface timeseries at Chebogue point. The model is thick balck, the observed are the circles and plus signs. The MOZART model is dashed. As you can see GEOS-Chem captures the afternoon values (there is strong night depletion due to the low BL, which we would not expect to resolve. ) The dashed lines are 2 CO events, there is no corresponding ozone peak. May 17 Hudman et al. [2004]; Goldstein et al. [2004]

ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH ATLANTIC IN SUMMER 2004 The 2nd and third parts of my thesis use observations from the ICARTT campaign, which as you know took place during the summer 2004. There were a large number of aircraft, satellitesurface components. Two major aircraft efforts were the INTEX-NA by NASA using the DC8 and ITCT 2k4 by NOAA using the WP3. The NOAA P3 stayed mostly in new england focusing on emission verification and chemical evolution of fine scale urban plumes. The NASA DC8 covered a larger region and focused on emissions and continental outflow. SCIENTIFIC OBJECTIVES Regional Air Quality Continental Outflow Transatlantic Pollution Aerosol Radiative Forcing

Lightning X4 over U.S. & distributed to tropopause Flash counts (flashes/km2/s) GEOS-CHEM SIMULATION Modifications from ICARTT constraints in blue (improved) NOx Lightning Emissions Lightning X4 over U.S. & distributed to tropopause [Price and Rind, 1992] We again use GEOS-Chem. Of special importance to this study - NOx lightning emissions are following the cloud top height raised to the fifth power of Price and Rind, scaled to match tropical ozone concentrations yielding 4.7 tg N/year. We use the NEI99 v1 EPA inventory over the U.S. with modifications to some VOCs based on past budget analysis. Due to the large fire year, we use a May-August 2004 fire inventory for North America developed by Solene Turquety.This model has been extensively tested and includes the latest findings in the description of the Noy budget over N. America as we presently understand it. NOx emission CO emissions EPA National Emissions Inventory 1999 v1 (w/ modifications to VOCs) Power plant and Industry NOx 50% Anthropogenic CO 60% May-August 2004 NA Fire Inventory [Turquety et. al, 2007]

GEOS-CHEM VS. ICARTT Mean comparison along the flight tracks Ozone FT bias 5-10 ppbv Large UT NOx bias BL bias in CO and NOx Using this simulation GEOS-Chem simulation sampled along the NASA DC-8 and NOAA WP3 flight tracks, we found some discrepancies in our current understanding of the North American NOy budget, particularly in upper tropospheric NOx and ozone concentration as well as in changes in emissions over the U.S. since 1999. Shown here in red are mean simulated profiles using our standard simulation. The black are mean observations. The WP3 and DC-8, shows a CO bias in the lowest two km, which Lee Murray discussed in his presentation yesterday. For NOx we also see a model high bias in the lowest two km. Striking are two features in the upper troposphere…elevated NOx underestimated in the model by a factor of 4 with current emissions estimates and a 5-10 ppbv bias in oxone throughout the free tropospheric over the U.S. with current emissions. Measurements (WP-3D, DC-8): CO (J. Holloway, G. Sachse), NOx (T. Ryerson, R. Cohen, W. Brune), PAN (F. Flocke, H. Singh), HNO3 (A. Neuman, J. Dibb), ozone (T. Ryerson, M. Avery)

ICARTT OBSERVATIONS CONFIRM LARGE DECREASE SINCE 1999 IN INDUSTRY/POWER SOURCE Large overestimate powerplant/industry dominated Midwest and in the South Model / Observed NOx (0-2 km) DC-8 Midwest Observed Simulated Improved Simulation [ratio] The NOx bias can be explained by a decrease in the powerplant/industry source by 50% between 1999-2004 as a result of the NOx SIP. This is evident in the Model/Observation ratio map. The largest discrepancy is over the midwest and in other powerplant dense regions. We reduced the powerplant/industry emission by 50% , greatly improving the NOx simulation at the surface. 50% reduction in power and industry source as determined by Frost et al., [2006] improves boundary layer NO2 simulation Hudman et al. [2006a,b] Measurements (WP-3D, DC-8): T. Ryerson (NO2), Ron Cohen/Tim Bertram (NO2)

MEAN AFTERNOON OZONE CONCENTRATIONS 0-1.5 KM DURING ICARTT SIMULATED (NEI99 stationary NOx source reduced by 50%) OBSERVED SIMULATED (NEI99) This figure shows observed and simulated mean 0-1.5 km afternoon ozone concentrations during ICARTT. Cool temperatures, cloudiness, and frequent frontal passages made summer 2004 a mild ozone season. Mean observed concentrations were typically 50-60 ppbv. High values observed offshore reflect aged urban pollution plumes deliberately sampled by the WP-3D aircraft in stratified air and should not be viewed as representative. The simulation using NEI 99 is too high over the United States by 5-15 ppbv, with a simulated-to-observed regression slope of 1.05 ± 0.10 (R2 = 0.30). he NOx reduction improves the ozone simulation in the South and Midwest, though it only slightly improves the overall model-to-observed ozone correlation (0.95 ± 0.07, R2 = 0.34). Stratified local plumes, not representative High bias in the South and Midwest improved simulated-to-observed regression slope (afternoon, overland, 0-1.5km): NEI 99: 1.05 ± 0.10 (R2 = 0.30); NEI 99 Reduced NOx: (0.95 ± 0.07, R2 = 0.34). Measurements (WP-3D, DC-8): T. Ryerson, M. Avery

OZONE REDUCTIONS RESULTING FROM DECREASE IN NOx EMISSIONS Regional differences in ozone, can be explained by Ozone Production Efficiency (OPE): OPE Midwest: 2.5-3.5 Southeast: 4-5.5 The NOx emission reductions are largest in the Midwest, reflecting the distribution of power plants. The largest resulting ozone decreases in the model are in the southeast, the midwest shows weaker decreases 4-6 ppbv. These spatial differences in the different responses to ozone can be explained by regional variations in OPE. OPE decreases with increasing NOx and increases with increasing isoprene and UV flux. The Midwest BL OPE is 2.5-3.5 where as the Southeast is 4-5.5, consistent with simulated ozone decreases. We next wanted to see how changes in OPE and NOx have led to changes in observed o3/co correlations, an in turn NA export. Observed O3/CO can be approximated as OPE * ENOX/ECO. But this requires a good CO source. Can we see changes in OPE due NOx emission reductions in dO3/dCO in U.S. outflow? Requires good estimate of CO source….. GRC Poster.

OZONE-CO CORRELATIONS SHOW DECADAL INCREASE Aircraft (0-1.5 km, 11-5pm LT) Chebogue Point ALL WIND DIRECTIONS WINDS FROM W-SE Overestimate of tropical background Here I am showing ozone/CO correlations from the DC-8 aircraft and the Chebogue Point surface site on the southern tip of nova ScotiaThe Aircraft data are from 11 am – 5pm, excluding fresh plumes. For chebogue point we show data from the W-SE which sampled NA outflow. ThedO3/dCO in the obse is 0.47 (R2=0.54) and the corresponding model ratio is 0.36 (R2-0.21). This is caused by an overestimate of the ozone background in the Southeast and tropical airmasses. Looking at the regions geographically, we found what really dominates this slope is emission from the NE U.S. The slope at Chebogue Point is lower 0.4, consistent although slightly lower than observations. The same problem exists with background as above. Previous studies found slopes of 0.3-0.4. The higher values could be due to decadal changes in U.S. CO and NOx emissions. Measurements (WP-3D, DC-8): CO (J. Holloway, G. Sachse), ozone (T. Ryerson, M. Avery). Syrface Measurments at Chebogue Point by D. Millet Obs during the early 90s show dO3/dCO ~ 0.3 – 0.4 [Parrish et al., 1998; Chin 1994] Change could be due to decadal changes in emissions

UT NOx OBSERVATIONS POINT TO A LARGER THAN EXPECTED LIGHTNING NOx SOURCE NOx (8-12 km) Observed GEOS-Chem (Lightning X4) [ppbv] NLDN Flash Comparison GEOS-Chem Here I am showing Observed NOx between 8-12 km. We saw very large values of NOx between 0.5-2 ppbv all the time. We argue that this is a lightning source. The aircraft source is well constrained, and convection doesn’t show a bias for bl species like propane. This doesn’t appear to be a NOx lifetime issue because if it were, we would expect when looking at a frequency distribution of NOx to see more variability in the model than in the observations. This isnt the case adding some support to the argument that OH is ok. [Flashes km2 s] NO: W. Brune, NO2: R. Cohen/T Bertram Hudman et al. [2007a]

MIDLATITUDE LIGHTNING PRODUCES MORE NOx/FLASH Over midlatitudes Ken Pickering shows a distribution flash production vs. IC/CG ratio of storms. The green and red are over the U.S. The blue are over Europe. The black like is the US. Median when using flash counts from NLDN. They predict 500 mol/flash. GEOS-Chem predicts ~125 mol/flash worldwide over the continents. So we increase this by a factor of 4. [Huntrieser et al., 2005] [Ken Pickering] Standard GEOS-Chem mean flash rate was 125 mol flash-1 (Improved  X4  500 mol flash-1)

OZONE COMPARISON INTEX-NA SOUTHEAST U. S OZONE COMPARISON INTEX-NA SOUTHEAST U.S. Increase in lightning yield X4 to 500 mol/flash has ~10 ppbv effect on ozone O3 NO2 2004 was not an anomalous lightning year Observed Simulated Improved Simulation When we do this. We find in th esouth NOx is completely corrected and it also corrects a 5-10 ppbv bias in ozoen throught the free troposphere. This suggests a great sensitivity to lightning changes under a warming cliimate. 2004 wasn’t an anomolous year. Here I am showing GEOS-Chem flashes over the U.S. and coastal waters and NLDN. The jump in 2001-2002 is due to upgarades completed late 2002. so the comparable years are 2003-2005. In both the model and NLDN there is not much interannual variabillty. Hudman et al. [2007a] …suggests great sensitivity of ozone to climate change

SUMMERTIME NORTH AMERICAN OZONE ENHANCEMENTS ICARTT DC-8 ~ Equal contributions for lightning and anthropogenic emissions in free troposphere and to NH burden NA Enhancement to Hemispheric Ozone North American Source NOx Emission (Tg N) Ozone Production Efficiency Hemispheric ozone enhancement (Tg, %) Lightning 0.28 32.5 9.1 (5.1%) Biomass burning 0.32 17.5 5.6 (3.1%) Fossil fuel 0.72 15 10.9 (6.1 %) All 1.32 19 25.6 (14.3 %) The ICARTT campaign offered cpmstraints on NOx emissions from anthropogenic emissions, lightning and biomass burning and implied large corrections for these. we developed a new estimate for North American contribution to hemispheric ozone. Here I am showing enhancements from these individual sources along the DC-8 flgiht tracks. The total North American enhancements amounts to 30 ppbv in the bioundary layer and 20 ppbv in the free troposphere. BL is mainly anthropogenic but in the free troposphere there are equal enhancements from lightning and anthropogenic emissions. Biomass added 2-4 ppbv to 4km and less above. Hudman et al. [2007b] Biomass Lightning Anthropogenic Simulated Observed All

BIOGENIC VS. ANTHROPOGENIC SOURCES OF CO OVER THE UNITED STATES Both aircraft and surface data suggest NEI 99 CO emissions are 2.5 times too high Measurments: J. Holloway, G. Sachse, A. Goldstein Aircraft (0-1.5 km) OBSERVED SIMULATED (NEI99) SIMULATED (anthro CO reduced by 60%) J. Holloway, G. Sachse GRC Poster