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Myojeong Gu 1 , Carl-Fredrick Enell 2 , Florence Goutail 3 , François Hendrick 4 ,

A comparison study of stratospheric NO 2 profiles among ground-based zenith sky DOAS, SCIAMACHY limb measurements and SAOZ balloon-measurements over Kiruna, Sweden. Myojeong Gu 1 , Carl-Fredrick Enell 2 , Florence Goutail 3 , François Hendrick 4 ,

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Myojeong Gu 1 , Carl-Fredrick Enell 2 , Florence Goutail 3 , François Hendrick 4 ,

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  1. A comparison study of stratospheric NO2profiles among ground-based zenith sky DOAS, SCIAMACHY limb measurements and SAOZ balloon-measurements over Kiruna, Sweden Myojeong Gu1, Carl-Fredrick Enell2, Florence Goutail3, François Hendrick4, Ulrich Platt5, Jean-Pierre Pommereau3, Janis Pukite1, Uwe Raffalski6, Michel Van Roozendael4, Thomas Wagner1 (1) Max-Planck Institute for Chemistry, Mainz, Germany (myojeong.gu@mpic.de) (2) EISCAT Scientific Association, Kiruna, Sweden (3) LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (4) Institut d'Aéronomie Spatiale de Belgique (IASB-BIRA), Brussels, Belgium (5) Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany (6) Swedish Institute of Space Physics, Kiruna, Sweden • Stratospheric NO2 • Measurements • Retrieval methods • Results 1

  2. Introduction: Stratospheric NO2 • Influence the ozone chemistry : dependingon the altitude. • Middle and upper stratosphere (25 – 40 km): NOx destruction of ozone NO +O3→ NO2 +O2 NO2 + O → NO +O2 NO2 +hv → NO + O [Crutzen, 1970] • Below 25km: acting as a buffer against halogen-catalyzed O3 loss through the formation of reservoir species (ClONO2, BrONO2). ClO + NO2→ ClONO2 BrO+ NO2→ BrONO2

  3. Introduction : Ground-based zenith sky DOAS Zenith • Zenith sky DOAS : • Records spectra of scattered sunlight in zenith direction. • Observation of stratospheric trace gases: during each twilight : Increasing sensitivity of measurement as a result of a long light path in stratosphere. observation of scattered sun light at zenith angles • Measurement site : Kiruna, Sweden: 68.84°N, 20.41°E • Good place to study the polar stratospheric chemistry. • Located in the arctic circle and is often situated under the polar vortex. Mountain wave induced Polar Stratospheric Clouds (PSCs) develop. • Installation of Zenith Sky DOAS • Measurement starts: December of 1996 and since then performed automatic measurements up to now. • Wavelength range: 300nm to 400nm

  4. Data Scheme Zenith sky DOAS meas. SCIAMACHY limb meas. SAOZ balloon NDACC Climatology AMFs LUT developed by CNES Langley plot method dSCDs dSCDs 2-D Retrieval [A] Profile IASB-BIRA algorithm NO2 profile profile Ground-based profile Smoothed profile AvK, a prior [B] Partial column VCDs Integrating profile Integrating 12 – 42 km

  5. Data Scheme • DOAS settings: • Wavelength range: 356-392 nm • Cross sections: NO2(Vandaele et al.1998, 220K) O3 (Bogumil et al.2003, 223K, 243K), O4(Greenblatt et al. 1990), Ring • Daily based reference spectrum (for each twilight, the spectrum closest to SZA 80°) IASB-BIRA NO2 profiling algorithm [Hendrick et al., 2004] • Mean scattering height depends on SZA • Based on the Optimal Estimation Method • Forward model (RTM + Photochemical model) Zenith sky DOAS meas. • SCIAMACHY NO2 profiles are retrieved from limb geometry measurement. • Altitude range : 12 – 42 km • Using 2-D retrieval approach [Pukite et al., 2010] • Coincidence criteria for comparison : • SCIAMACHY observations on same day. Closest coincidence event within 1000km is chosen. SCIAMACHY limb meas. • SAOZ balloon gondola using UV-Visible spectrometer [SAOZ team] • NO2 spectral window: 450 – 526nm • This study, all balloon measurements were launched at Kiruna. • Coincidence criteria for comparison: SAOZ balloon measurement on same day. Using the evening ascent measurement. SAOZ balloon

  6. Langley plot methods Zenith sky DOAS meas. NDACC Climatology AMFs LUT 2013, Day Number: 145 Langley plot method dSCDs Plotting the DSCD(θ) as a function of AMF(θ) : The slope and ordinate of the curve refer to VCDs for NO2 and SCDref, respectively. SCDref: Actual amount of NO2 in the reference spectrum VCDs !! Langley plot will be affect by Photochemistry. Tends to overestimate true VCD.

  7. Results (1): Profiles

  8. Measurement response 2005/Apr/21 @AM 2005/Apr/25 @PM SCIAMACHY Zenith sky DOAS These red and blue line indicates sum of the rows of the averaging kernels. Meas. responses in AM and PM: similar to each other High sensitivity: 13 km to 38 km (SCIAMACHY), 18 km to 45 km (Zenith sky DOAS)

  9. Seasonal mean profile (2002 – 2006) Spring AM (#112) Spring PM (#88) • Spring : March-May • Summer: Mid Jun - Aug Retrieved from zenith sky DOAS (blue) Unsmoothed SCIA profile (black) Smoothed SCIA profile (red) a prior (grey) Error bar: standard deviation Smoothed profile Xsmoothed_scia=Xa+A(Xscia– Xa) Relative difference= Summer AM (#80) Summer PM (#87) NO2 conc. [molec/cm2]

  10. Comparison of zenith sky DOAS profile and SCIAMACHY limb profile : Monthly mean profile (2002 – 2006) @AM (#31) (#31) (#31) (#31) (#49) (#49) (#49) (#49) (#49) (#40) (#40) (#40) (#40) (#40) Error bars: standard deviation Feb Mar Apr (#19) (#19) (#37) (#37) (#37) (#32) (#32) • - Good agreement • Small rel. diff • 20 – 30 km: seasonal variation Jun May Jul (#18) (#14) (#24) Oct Aug Sep

  11. Comparison of zenith sky DOAS profile and SCIAMACHY limb profile : Monthly mean profile (2002 – 2006) @PM (#19) (#43) (#42) Error bars: standard deviation Feb Mar Apr (#30) (#15) (#26) - Good agreement - Similar to measured @AM - Rel. diff: larger deviation May Jun Jul (#11) (#6) (#22) Oct Aug Sep

  12. Comparison of zenith sky DOAS and SAOZ balloon measurement Zenith sky DOAS (blue) SAOZ balloon (red) Smoothed SAOZ balloon (magenta) Overall similar pattern regarding the magnitude and peak altitude. However, no perfect agreement can be expected.→ non-coincidence of both measurement and influenced by metrological effect.

  13. Potential vorticity on the isentropic surface of 475K 1997. 03. 20. 18h Sun position 75°N Balloon trajectory 72°N Zenith sky DOAS SAOZ balloon 69°N Smoothed SAOZ balloon 66°N 63°N 60°N SAA≈80° SZA≈88° 16:00 UTC 30°E 5°E 25°E 10°E 15°E 20°E [ECMWF]

  14. Results (2): Partial columns

  15. Comparison of NO2partial columns @ AM 2005 2006 NO2 column [molec/cm2] Relative diff. [%] smoothed SCIA – DOAS/DOAS [%] Langley plot method-DOAS/DOAS[%] - Good temporal agreement - Spring period: large variations - At the beginning of the year, VCDs (Langley methods) are small.← Rel. diff. large

  16. Comparison of NO2partial columns @ PM 2005 2006 NO2 column [molec/cm2] Relative diff. [%] smoothed SCIA – DOAS/DOAS [%] Langley plot method-DOAS/DOAS[%] - Langley plot results: larger than other profile inversion groups. → Langley plot methods would be overestimated due to the photochemistry.

  17. Summary • In this study, we retrieve stratospheric NO2 profile measured from ground-based zenith sky DOAS using IASB-BIRA profiling algorithm and compare it with SCIAMACHY limb measurements and Balloon measurements. • Results from the retrieval NO2 profile and partial columns agree generally well SCIAMACHY and SAOZ balloon measurements. Outlook: Need for a new criterion to find coincident events. • In this work, we used the location of the Kiruna instrument to calculate the distance to the SCIAMACHY measurement. • In the near future, we will use the air volume for reaching a measurement most sensitive (several hundreds kilometer towards the sun to calculate the distance to the other measurements → 2-D box AMFs)

  18. Thank you for your attention! myojeong.gu@mpic.de

  19. NDACC Climatology AMF LUTs

  20. 1997. 03. 20. 18h 75°N 72°N 69°N 66°N 63°N PV 475K 60°N Tropopause 30°E 5°E 25°E 10°E 15°E 20°E

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