Workshop on Integrated Observations for Assessing Hemispheric Transport. Geneva, Switzerland, 24-26 January 2007.An analysis of the consistency of lower-FT observations with chemical transport model (CTM) simulations in aged U.S. export

Fialho, Paulo

Helmig, Detlev

Honrath, Richard

Li, Q. B.

Owen, Robert

Repositório da Universidade dos Açores

Photochemical evolution of continental outflow to Pico Mountain (Azores):Integrating observations with CTM simulations in lower-FT outflowR. E. Honrath1, R. C. Owen1, Q. B. Li2, D. Helmig3 and P. Fialho41 Environmental Engg.,/Atmos. Sci., Michigan Tech;reh@mtu.edu 2 Jet Propulsion Laboratory, Caltech; qinbin.li@jpl.nasa.gov3 Institute of Arctic and Alpine Res., Univ. Colorado;detlev.helmig@colorado.edu 4 Univ. Azores, Portugal; paulo.fialho@angra.uac.pt1 SynopsisAn analysis of the consistency of lower-FT observationswith chemical transport model (CTM) simulationsin aged U.S. export.•Measurements: Pico Mountain lower-FT observatory,∼4–8 days downwind of the N. American east coast.•CTM simulations: GEOS-Chem simulations for 2005.• Events occurred in both observations and CTM simulations.• Analyzed using new tools that combine CTM simulations withFLEXPART retroplumes to probe the evolution of CO, O3, andOH in the export events in conjunction with the observations.– FLEXPART retroplumes define where the air ultimatelysampled at Pico was, at specified times upwind.– By convolving GEOS-Chem output with the retroplume, onecan calculate the mixing ratio that would reach Pico if allchemistry ceased from that point forward.– This allows probing the chemical evolution in the CTM in asemi-lagrangian fashion.– This analysis is shown in section 4.– (More info: see Handout: Owen et al. AGU poster.)2 Evidence ofdiscrepanciesComparisons between in-situ observations and GEOS-CHEMsimulations sampled at the location of the Pico station revealseveral differences deserving further study. Two such comparisonsare shown here.O3 seasonal cycle.Shown: Pico 2001–2005, Pico 2005, and GEOS-Chem, 2005.Boxes show middle 50%, whiskers show middle 90%.203040506070Ozone (ppbv)            Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec•Observed O3 variability is greatest during summer.– The magnitude of this increase is underestimated by the model.–Our focus here is on the high summertime O3 observations.Most high-O3 observations are associatedwith increased CO in U.S. outflow orboreal fire plumes.Pico and GEOS-CHEM spring 200560 80 100 120 140 160 180 20020406080slope=  0.64(  0.30-  1.37)Int=-32.70r^2=    0.221N=1394slope=  0.50(  0.30-  0.82)Int= -7.27r^2=    0.369N=465slope=  0.23(  0.22-  0.24)Int= 21.90r^2=    0.918N=4440 80 120 160CO (ppbv)20406080Ozone (ppbv)Measurements(black) andsimulations (magenta)for summer 2005. Solidsymbols indicate U.S.,European, or borealfire outflow.3 Characterization ofclear U.S. outfloweventsContinuous measurements allow sampling of clear outflow events,among many additional events that mix anthropogenic andbiomass-burning impacts.• Two clear events of U.S. outflow in the lower free troposphereoccurred during August 2005.• Transport pathway: from FLEXPARTFLEXPART retroplume residence times:well-organized transport from the east coast.Case 1: Arrives 18:00 Aug. 9, 2005FLEXPART indicates average height over the ocean = 2.5 to 4 km.• The event is simulated by GEOS-Chem.GEOS-Chem CO simulation, 4 days upwind.Black outline: location of air to reach Pico.GEOS-Chem O3 simulation, 4 days upwind.Black outline: location of air to reach Pico.4 Analysis and interpretation combining observations,FLEXPART, and GEOS-ChemOzone vs CO, at Pico and upwind in GEOS-ChemCase 1. August 9–11 event (transport shown in part 5 to the left).O3 vs CO80 90 100 110 120 130 140 150CO (ppbv)40506070Ozone (ppbv)0.41.11.92.63.44.14.9Pico observationGEOS-Chem at PicoGEOS_Chem upwindRed circles: Pico observations,Blue diamonds: GEOS-Chem simulations at Pico.•GEOS-Chem simulates correlated CO and O3 enhancements during this event.• The Pico observations also exhibit enhanced CO and O3, with 2 key differences:– The range of enhancement is larger than simulated. This could reflect dilution in themodel grid cells.– There is a group of observations with much higher O3 than expected from theGEOS-Chem O3-CO slope and the observed CO.• To investigate the cause, we convolved the GEOS-Chem simulations using theFLEXPART retroplume. This produced theBlack line: FLEXPART retroplume sampling of GEOS-Chem simulations to givemixing ratios at Pico if all chemistry stopped after the indicated number of days upwind.• The upwind GEOS-Chem values (numerals) lie above and to the left of the blue lineextrapolated from the GEOS-Chem (at Pico) points. This indicates the importance of netO3 destruction in the simulations.• For the circled Pico observations, [O3] corresponds to levels simulated up to 3.5 daysupwind (2 to 4 days after export), but CO values are within the range simulated at Pico(and below levels simulated 3 days upwind).GEOS-Chem sampled upwind6 5 4 3 2 1 0Days upwind80100120140160180CO (ppbv)CO (ppbv)4550556065707580Ox (ppbv)02•1064•1066•1068•1061•107OH (molec/cm3)Inspection of the FLEXPART-sampled GEOS-Chem simulationsprovides additional insight.The plot to the left shows the CO and O3 that would reach Pico if all chemistry ceased after theindicated number of days before arrival.Red: GEOS-Chem upwind CO.Blue: GEOS-Chem upwind Ox.Black dotted line: Average OH at the upwind locations.• The CO and O3 lines would be flat and horizontal if no chemistry occurred and GEOS-Chemtransport matched FLEXPART transport. (See Owen et al. poster handout for details.)• The rapid drop starting at −5 days corresponds to export from N. America and indicates thatdilution in GEOS-Chem exceeds that in FLEXPART.• Additional O3 loss due to net photochemical destruction (circled) is evident between days 5 and4, and between days 4 and 3. (Daytime can be identified by peaks in upwind [OH].)Case 2: Aug 3–560 70 80 90 100 110CO (ppbv)3040506070Ozone (ppbv)0.41.11.92.63.44.14.95.66.47.17.9Pico observationGEOS-Chem at PicoGEOS_Chem upwind• This event traveled north of Pico, then looped around the back of the Azores high.Travel time from N. America was ∼7 days.•GEOS-Chem simulated the event, but its pathway diverged from FLEXPART’s 3 to 4 daysupwind of Pico. As a result, the GEOS-Chem at Pico points are do not show the event.•Using the upwind FLEXPART+GEOS-Chem method, that does not prevent analysis of this event.• The upwind time series (not shown) indicates significant simulated O3 loss in this event also.The total O3 decline after export was ∼25 ppbv, similar to Case 1.• The O3 levels observed at Pico during this event (circled) are again consistent with O3 simulatedby GEOS-Chem well upwind (4–6 days upwind, or 1–3 days after export). This suggests that O3destruction was overestimated.Contrasting springtime case: April 21–24.130 140 150 160 170 180 190CO (ppbv)505560657075Ozone (ppbv)0.41.11.92.63.44.14.9Pico observationGEOS-Chem at PicoGEOS_Chem upwind• Significant enhancements in CO (and in HCs and NOy, not shown) occurredduring this spring event. However,• only a ∼10 ppbv drop in O3 is simulated, mostly due to dilution.(Note that Y-axis range is reduced in this plot.)• The observed and simulated O3-CO relationships agree well during this event.The absence of a significant discrepancy here is consistent with the lack ofsimulated O3 loss in transit.Conclusions• Ozone enhancements observed at Pico during well-defined U.S.-outflow events are larger than expectedbased on GEOS-Chem simulations.• Analysis of simulations upwind of Pico indicates that O3 peaks observed in the analyzed events aresimilar in magnitude to O3 simulated well upwind.– This suggests that O3 is more efficiently transported over the N. Atlantic Ocean than simulated, i.e.with less gross destruction or with greater gross production.– This discrepancy is probably not limited to the GEOS-Chem CTM (e.g., [1]).• The method used here—convolving lagrangian particle model retroplume simulations with 3-D CTMsimulations to investigate transport and photochemistry—should be broadly useful for analysis ofmodels and measurements.• Although this analysis was limited to anthropogenic impacts, boreal wildfires affect Pico O3 levels to asimilar or even greater degree [12–14].Pico station status• Michigan Tech donated the station infrastructure to Portugal in June, 2006, in order to jump-startdevelopment of a permanent Portuguese station.• Continuing station development is aimed toward creating a long-term Global Atmosphere Watch (GAW)observatory. See the Helmig poster for information on an EU effort to do this, and see the Fialho posterfor more information on Azores atmospheric studies.• Measurements in the near future are dependent on new funding.ReferencesHandouts are available for the large-font papers.[1] Chandra, S. et al., Elevated ozone in the troposphere over the Atlantic and Pacific oceans in the northern hemisphere, GRL, doi:10.1029/2004GL020821, 2004.[2] Liu, X. et al., First directly-retreived global distribution of tropospheric column ozone from GOME: Comparison with the GEOS-CHEM model, JGR,doi:10.1029/2005JD006564, 2005.[3] Ziemke, J. R. et al., Tropospheric ozone determined from Aura OMI and MLS: Evaluation of measurements and comparison with the Global Modeling Initiative’schemical transport model, JGR, doi:10.1029/2006JD007089.[4] Owen, R. C., O. R. Cooper, A. Stohl, and R. E. Honrath (2006), An analysis of the mechanisms of NorthAmerican pollutant transport to the central North Atlantic lower free troposphere, JGR,doi:10.1029/2006JD007062.[5] Neuman, J. A., et al. Reactive nitrogen transport and photochemistry in urban plumes over the North Atlantic Ocean, JGR, doi:10.1029/2005JD007010, 2006.[6] Honrath, R. E. et al., Regional and hemispheric impacts of anthropogenic and biomass burningemissions on summertime CO and O3 in the North Atlantic lower free troposphere, JGR,doi:10.1029/2004JD005147, 2004.[7] Kleissl, J., et al., The occurrence of upslope flows at the Pico mountain observatory: a case study oforographic flows on small, volcanic islands, JGR, doi:10.1029/2006JD007565, in press, 2007.[8] Tanner, D., D. Helmig, J. Hueber and P. Goldan, A gas chromatography system for the automated, unattended, and cryogen-free monitoring of C2 to C6non-methane hydrocarbons in the remote troposphere, J. Chrom. A., 1111, 76–88, 2006.[9] Helmig, D. et al., Analysis of air transport and oxidation chemistry in the North Atlantic region from interpretation of non-methane hydrocarbon (NMHC)measurements at Pico Mountain, Azores, JGR, in prep., 2006.[10] Greenberg, J. P., D. Helmig and P. R. Zimmerman, Seasonal measurements of nonmethane hydrocarbons and carbon monoxide at the Mauna Loa Observatoryduring MLOPEX-2, JGR, 101, 14581–14698, 1996.[11] Jobson, B. T. et al., Seasonal trends of isoprene, C2–C5 alkanes, and acetylene at a remote boreal site in Canada, JGR, 99, 1589–1599.[12] Lapina, K., R. E. Honrath, R. C. Owen, and M. Val Martin, Evidence of significant impacts oflarge-scale boreal fires on ozone levels in the midlatitude Northern Hemisphere free troposphere, GRL,doi:10.1029/2006GL025878.[13] Val Martı´n, M. et al., Observations of significant enhancements of nitrogen oxides and ozone in theNorth Atlantic lower free troposphere resulting from boreal wildfires, JGR, doi:10.1029/2006JD007530,2006.[14] Pfister, G. G. et al., Ozone production from the 2004 North American boreal fires, doi:10.1029/2006JD007695, in press, 2006.AcknowledgementsThis research was supported by: NOAA Climate Program, NSF Atmospheric Chemistry, and INTERREG,the Governo Regional dos Ac¸ores (Portugal), and the Fundac¸a˜o para a Cie´ncia e Tecnologia (FCTPortugal).

Photochemical evolution of continental outflow to Pico Mountain (Azores): Integrating observations with CTM simulations in lowerFT outflow.

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Photochemical evolution of continental outflow to Pico Mountain (Azores): Integrating observations with CTM simulations in lowerFT outflow.

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