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Retrieval of CHOCHO from MAX-DOAS measurements in the Beijing area

This paper discusses the retrieval of CHOCHO vertical profiles using MAX-DOAS observations in the Beijing area. It also describes correlative data sets and presents results on seasonal and diurnal variations and the glyoxal:formaldehyde ratio.

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Retrieval of CHOCHO from MAX-DOAS measurements in the Beijing area

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  1. Retrieval of CHOCHO from MAX-DOAS measurements in the Beijing area F. Hendrick1, C. Gielen1, C. Lerot1, T. Stavrakou1, I. De Smedt1, C. Fayt1, C. Hermans1, J.-F. Müller1, G. Pinardi1, R. Volkamer2, P. Wang3, and M. Van Roozendael1 1Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium 2Dept. of Chemistry and Biochemistry, University of Boulder, Colorado 3Institute of Atmospheric Physics/CAS, Beijing, China 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 1

  2. Outline • Introduction – glyoxal in the atmosphere • CHOCHO vertical profile retrieval from MAXDOAS observations in the Beijing area • Description of correlative data sets: • CHOCHO VCD from OMI and from the 3D-CTM IMAGES • Results: • CHOCHO seasonal and diurnal variations • Glyoxal : Formaldehyde ratio • Optimal Estimation versus geometrical approximation • Conclusions 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 2

  3. Photolysis OH oxidation Conversion to SOA Dry and wet deposition Fires (d), 12% Fires (i), 8% Anthr.(d), 3% Biog. 51% Anthr.(i), 26% Introduction: Glyoxal in the atmosphere Sinks Sources Oxidation of NMVOCs CHOCHO (lifetime: 2-4h) Direct emissions from fuel combustion biomass burning Measuring this species is of major importance in air quality issues 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 3

  4. MAX-DOAS observation sites Institute of Atmospheric Physics (06/2008 - 04/2009) (03/2010 till now ) • Elevation angles: 2°, 4°, 6°, 8°, 8°, 10°, 12°, 15°, 30°, 90° (zenith) • Measurements from ~85°SZA sunrise to 85°SZA sunset • 15’ per scan 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 4

  5. DOAS settings • Fitting window: 434-460 nm • Fitted species: • CHOCHO (296 K) • NO2 (220 and 298 K) • O3 (223 K) • O4 (293 K) • H2O (296 K) • Ring effect • CHOCHO XS: Volkamer et al. (2005) at 296 K 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 5

  6. bePRO profiling tool Clémer et al., AMT, 2010 MAXDOAS measurements LIDORT Apriori Atm: P,T Surface albedo Trace gas: , profile Aerosol: optical prop. DOAS CHOCHO DSCD O4 DSCD DSCD Weighting functions Optimal estimation Aerosol vertical extinction profiles Wavelength: • O4: 477 nm • CHOCHO: 455 nm Tropospheric HONO vertical profiles with SH=0.5km and SH=1.0 km A priori profile: 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 6

  7. CHOCHO vertical profile retrieval Mean daytime CHOCHO profile Xianghe (2010-2013) Xianghe, 23 June, 2010, 16:22 LT/54°SZA • Selection of ‘good’ scans based on: • RMS (SH=0.5 km gives the lowest RMS) • DOFS (>1) • Multiple scattering (O4DSCDs) flag (Gielen et al., 2014) 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 7

  8. OMI glyoxal retrieval algorithm • Original algorithm developed for GOME-2A in 2010 (Lerot et al., ACP). • Recently updated and adapted to OMI. • Relies on the standard DOAS approach. Fitting window: 435-460 nm • Slant column retrieval • Conversion to vertical columns • Row-dependent background correction procedure (based on Pacific sector) • Air mass factors computed using a priori profile shapes provided by • the CTM IMAGESv2 over lands. • Airborne MAX-DOAS TORERO profile over oceans. • No cloud correction applied. Only pixels with cloud fraction < 20% are kept. 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 8

  9. 3D-CTM IMAGES • Resolution: 2°x2.5° • Meteorological fields: ECMWF • Emission inventories: • Biogenic: MEGAN Anthropogenic: REAS (Regional Emission inventory in Asia) • Pyrogenic: GFEDv3.1 • NMVOC species: 22 explicit IMAGES: Stavrakou et al., ACP, 2013 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 9

  10. Time-series of CHOCHO VCD Vertical column density • Good agreement between OMI (100km overpass) and MAX-DOAS • Smoothing of MAX-DOAS profiles with OMI AVKs improves the agreement between both data sets. • Observed seasonality can be mainly explained by larger biogenic and pyrogenic activities in summer Unsmoothed MAX-DOAS Smoothed MAX-DOAS (x1E15 molec/cm2) (x1E15 molec/cm2) (x1E15 molec/cm2) 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 10

  11. Diurnal variation of CHOCHO Vertical column density Local time (h) Local time (h) Local time (h) Local time (h) Near-surface concentration (0-200m layer) Local time (h) Local time (h) Local time (h) Local time (h) 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 11

  12. Comparison with 3D-CTM IMAGES Vertical column density normalized WRT local noon Vertical column density Liu et al., GRL, 2012: underestimation of aromatics (BTX) by a factor of 5-6 in the current anthropogenic emission inventories over China 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 12

  13. Glyoxal : Formaldehyde ratio CHOCHO:HCHO ratio RGF often used as an indicator of changes in VOC mixture: • Previous studies on this ratio: • Vrekoussis et al. (2010) – based on GOME-2: • RGF < 0.04 in urban areas • RGF > 0.06 in rural environments • Di Gangi et al. (2012) – based on in situ measurements during two campaigns: • RGF < 0.02 for biogenic regimes • RGF ~= 0.025-0.035 for polluted air masses • Kaizer et al. (2015) – based on airborne in situ measurements: • RGF < 0.025 for areas with high isoprenes emissions • RGF >0.03 for areas with high monoterpenes emissions • RGF can increase in case of local emissions (oil and gas production) 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 13

  14. MAX-DOAS and OMI HCHO observations over Beijing/Xianghe De Smedt et al., AMTD, 2015 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 14

  15. Glyoxal : Formaldehyde ratio • CHOCHO/HCHO VCD ratio is ranging from 0.025 to 0.055, except in DJF (0.05-0.09) • A good consistency is found with OMI • Higher RGF values are found during the winter where anthropogenic emissions are the largest Results more consistent with Di Gangi and Kaizer than with Vrekoussis 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 15

  16. Geometrical approximation vs OEM: CHOCHO OEM SH=0.5km OEM SH=1.0km 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 16

  17. Geometrical approximation vs OEM: HCHO OEM SH=0.5km OEM SH=1.0km 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 17

  18. Geometrical approximation vs OEM: CHOCHO OEM SH=0.5km OEM SH=1.0km 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 18

  19. Geometrical approximation vs OEM: CHOCHO 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 19

  20. Concluding remarks • Tropospheric CHOCHO vertical profiles and corresponding column densities have been retrieved in the Beijing area by applying an OEM-based profiling tool to MAX-DOAS observations from June 2008 till December 2013 • A good consistency is found between MAX-DOAS and OMI in terms of CHOCHO VCD seasonality (maximum in summer and a minimum in winter) • MAX-DOAS CHOCHO VCD has a maximum around local noon in the Beijing City centre, in reasonably good agreement with simulations from the 3D-CTM IMAGES; no marked diurnal variation is found in Xianghe • CHOCHO/HCHO VCD ratio is ranging from 0.025 to 0.055, except in DJF (0.05-0.09). A good consistency is found with OMI. • Further investigations: • Consistency between OEM and geometrical approximation • Comparison with the 3D-CTM IMAGES (surface concentration + different emission scenarios) 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 20

  21. Acknowledgements • Belgian Federal Science Policy Office, Brussels (PRODEX and AGACC-II projects) • EU FP7 projects NORS and MarcoPolo Thank you for your attention ! 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 21

  22. CHOCHO and HCHO diurnal variations Vertical column density normalized WRT local noon 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 22

  23. Geometrical approximation vs OEM: CHOCHO and HCHO at Bujumbura (Burundi) CHOCHO OEM SH=1.0km HCHO OEM SH=1.0km 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 23

  24. Multiple scattering (O4) flag O4 flag Gielen et al., AMT, 2014 214.2 214.3 214.7 214.4 214.5 214.6 Fractional day Strong temporal variability of O4 DSCDs due to enhanced multiple scattering commonly occurs in optically thick clouds, and is seen less for high aerosol optical depth 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 24

  25. OMI retrieval of CHOCHO VCDs • Original algorithm for GOME-2A developed in 2009 (Lerot et al., ACP, 2010) • Two steps: slant column retrieval (DOAS) + conversion of SCDs to VCDs • Algorithm updates: • Strong focus on GOME-2A/OMI consistency: Application of common settings to both sensors. • DOAS fit • Update of cross-section data base. • On-line convolution of cross-sections with a fitted slit function (for GOME-2A). • Daily mean background radiance spectrum as the reference instead of solar spectra. • Normalization procedure • Row- (OMI) or VZA-dependent (GOME-2) procedure • AMF computation • Over lands: A priori profiles provided by an updated version of the CTM IMAGES. • Over oceans: use of a fixed a priori profile (TORERO). • Extension of the weighting function LUT. • No cloud correction any more, only pixels with CF<0.2 are kept.  Reduction of the influence of the a priori information. 7th International DOAS Workshop, 6-8 July 2015, Brussels, Belgium 25

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