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Comparison of Airborne and Ground-based NO2 Observations in Bucharest

Study comparing airborne imaging DOAS measurements of NO2 with ground-based observations in Bucharest during AROMAT. Analysis includes instrument setup, VCD derivation, results, and comparisons with mobile Car-DOAS measurements. Findings suggest potential systematic issues in VCD estimation.

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Comparison of Airborne and Ground-based NO2 Observations in Bucharest

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  1. Comparison of airborne imaging DOAS measurements of NO2 with ground based observations in Bucharest during AROMAT Andreas Meier1, Anja Schönhardt1, Andreas Richter1, André Seyler1, Daniel Eduard Constantin2, Reza Shaiganfar3, Alexis Merlaud4, Thomas Ruhtz5, Carsten Lindeman5, John P. Burrows1 DOAS Workshop, Brussels 2015-07-08 1 University Bremen 2 University Galati 3 Max-Planck Institute for Chemistry 4 BIRA 5 FU Berlin

  2. Outline • The instrument • Deriving Vertical Column Densities • Results • NO2 VCDs over Bucharest • Comparison • AirMAP vs. AirMAP • Comparison to mobile Car-DOAS measurements • Summary

  3. AirMAP Pictures AirMAP on FU Berlin Cessna Pushbroom imaging DOAS instrument for NO2 (and SO2)

  4. Instrumental setup • Collection of scattered sun light from below aircraft • Fed into imaging spectrometer via ordered fiber bundle, retaining spatial information • Dispersion with ruled grating • Spectra recorded with frame transfer CCD, allowing gapless mapping

  5. AirMAP viewing geometry qopening angle/FOV across track ~ 48° qiindividual viewing angle of direction i (max. 35) gopening angle/FOV along track ~ 1.5° ssidelengthsof pixel across track wside length of pixel alongtrack H flightaltitude ~ 3000m vaircraft speed (typ. 60m/s) texpexposure time typ. 0.5s

  6. DOAS retrieval NO2

  7. Deriving Vertical Columns • Calculation of BAMFs for different conditions • Choose matching conditions for spectrum i: Geometric approximation for LOS: • -const.: * profile: 1km * nadir * no aerosols-var: * SZA * flight altitude * albedo • * SZA • * Flight altitude • * Albedo

  8. Spatial dimensions OMI pixel 13 x 24 km2 S5p pixel 7x7 km2

  9. NO2 VCDs over Bucharest NO2 VCD 14-09-08 (Monday) 12:04 – 13:35 EEST | SZA: 39° – 43° Gridsize 0.0008° x 0.0008° ≈ 90x60m N 0-1 m/s W E OMI pixel 13 x 24 km2 S5p pixel 7x7 km2 S

  10. NO2 VCDs over Bucharest NO2 VCD 14-09-09 (Tuesday) 10:52 – 12:12 EEST | SZA: 41° – 50° Gridsize 0.0008° x 0.0008° ≈90x60m N 2-3 m/s W E S

  11. Airmap vs Airmap

  12. Data used • A lot of overlap of the subsequent tracks • Temporal difference: ≈ 1-20 min Aircraft heading West Aircraft heading East

  13. AirMAP vs AirMAP in overlap

  14. Summary AirMAP • AirMAP measured successfully NO2 VCD over Bucharest • Measurements on subsequent days reveal large inter-day variability • The results are consistent for co-located measurements • Snapshot assumption holds (stable NO2 field) • The presented standard deviation of the measurements is not only noise but also: • Errors in ground pixel location matching • Different integration volume • Variability in NO2

  15. AirMAP vs mobile CAR doas

  16. AirMAPvs. Uni Galati Car-DOAS • Zenith • 425 – 490 nm • Grid size: 0.003° x 0.003°

  17. AirMAP vs MPIC Car-DOAS • 22° elevation angle • 400 - 448 nm • Grid size: 0.003° x 0.003°

  18. Summary AirMAP vs mobile Car DOAS • The comparison looks good, but: • Car-DOAS yields larger VCD • Looks like a systematic problem • …due to profile / sensitivity / dilution? • Who over or under estimates? • Spatial averaging? • Derivation of VCD has to be further homogenized • E.g. BG-VCD, aerosols…

  19. Thank you! • Funding • Sharing data • Daniel-Eduard Constantin • Reza Shaiganfar • Alexis Merlaud • Thomas Ruhtz

  20. Fig 5a: Comparison between AirMAP and UGAL Car-DOAS NO2 DSCDs: Pixel-wise correlation plot of NO2DSCDs of co-located measurements of AirMAP pixels and car positions. The dashed line represents a 1:1 relationship. AirMAPvs UGAL DSCDs

  21. BL=1000 grd=8e-4 Air mass factors

  22. BL=1000 grd=8e-4 Derived albedo Source: Herold at al. 2004

  23. Differences absolute Zenith 22°

  24. Location

  25. VCD I / AMF • BAMFs calculated for different conditions (SCIATRAN) • SZA • Flight altitude • Albedo • Profile: Box (1km well mixed) • Nadir • No aerosols • AMFsel • Albedo:

  26. Data: • Gridded to 8e-4°x 8e-4° (90 x 64 m2) • Filtered for: • altitudes > 2900m • Roll < -/+ 10° • Time: 9:04 – 10:45 UTC (LT +2) • SZA: 39° - 43°

  27. Data: • Gridded to 3e-3°x 3e-3° (333 x 238 m2) • Filtered for: • altitudes > 2900m • Roll < -/+ 10° • Time: 9:04 – 10:45 UTC (LT +2) • SZA: 39° - 43°

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