1. TEMIS user workshop, Frascati, 8-9 October 2007 Tropospheric Formaldehyde (CH 2 O) from Satellite Observations. Isabelle De Smedt 1, M. Van Roozendael 1, R. Van Der A 2, H. Eskes 2. 1: BIRA-IASB, 2: KNMI

2. TEMIS user workshop, Frascati, 8-9 October 2007 Formaldehyde in the troposphere NOx/VOCs ratio determines the production of ozone in the troposphere. Satellite observation of NO 2 and CH 2 O support air quality control. CH 2 O is one of the most abundant carbonyl compounds and a central component of VOCs oxidation. Its observation can help to constrain VOC emissions. Sources: - Methane oxidation (background) - Biogenic VOCs oxidation (isoprene) - Anthropogenic hydrocarbon oxidation - Biomass burning (as first and secondary product) Sinks : Oxidation by OH radical and Photolysis - Major source of CO - Production of HO 2 CH 2 O has a spectral signature of absorption in the near UV and can therefore been retrieved from satellite observations with the DOAS technique.

3. TEMIS user workshop, Frascati, 8-9 October 2007 The TEMIS Project Objective within the TEMIS project: improve the quality of CH 2 O retrieval from satellite and provide a consistent long term series of CH 2 O observation combining different instruments. Two satellite instruments: 1.GOME on ERS2: –launched in 1995. Full coverage until June 2003. –320 x 40 km 2 ground pixel –sun-synchronous orbit, 10:30 –global coverage in 3 days 2.SCIAMACHY on ENVISAT: –launched in 2002. –60 x 30 km 2 ground pixel –sun-synchronous orbit, 10:00 –global coverage in 6 days

4. TEMIS user workshop, Frascati, 8-9 October 2007 DOAS technique in two independent steps: 1.Fit of slant columns (absorption along the satellite viewing path). SCD are retrieved with the WINDOAS software. 2.Determination of air mass factors to obtain vertical columns. AMF are computed with radiative transfer calculations to model scattering in the troposphere and CH 2 O profile shape from 3D-CTM. The TEMIS Project Tropospheric CH 2 O is a joined product between BIRA-IASB and KNMI.

5. TEMIS user workshop, Frascati, 8-9 October 2007 1: CH 2 O Slant Columns In UV, main absorbers are Ozone and Ring effect. CH 2 O optical depth smaller. Optical densities: SC.σ(λ) SC O 3 = 2x10 19 mol/cm² SC NO 2 = 5x10 16 SC CH 2 O = 1x10 16 SC BrO = 1x10 14 Fit very sensitive to: S/N ratio Other molecules absorption Fitting window DOAS corrections

6. TEMIS user workshop, Frascati, 8-9 October 2007 1: CH 2 O Slant Columns DOAS settings have been optimized in order to obtain a consistent time series combining the two instruments. Particularly, the fitting windows has been shifted more in the UV to avoid a spectral artefact in SCIAMACHY spectra. I 0 : radiance selected daily in the Pacific Ocean. Reference sector correction based on the background of CH 2 O in the Pacific only due to CH 4 oxidation.

7. TEMIS user workshop, Frascati, 8-9 October 2007 Compared to first version of the TEMIS GOME CH 2 O product, SCD have been analysed in a new fitting window (328.5-346 nm). For GOME: Reduction of the background noise and several artefacts above desert regions. For SCIA: Allows to retrieve CH 2 O consistent with GOME. GOME CH 2 O SCD [x10 15 mol/cm²] 1997-2002 1: CH 2 O Slant Columns

8. TEMIS user workshop, Frascati, 8-9 October 2007 2: AMF Determination Scattering by clouds and air particles makes the AMF dependant on the vertical distribution of the molecule. Scattering properties of the atmosphere modelled with a RTM (Disort). WF depend on observation angles, cloud properties, albedo and ground Altitude. Cloud Correction based on the independent pixel approximation and on the FRESCO product. Vertical distribution of CH 2 O is taken from the tropospheric 3D-CTM IMAGES. The profile shape S(z) is the normalized profile: S(z) = P(z)/∫P(z). WF Profile as seen by GOME Intex-A campaign Jul.2004 NCAR URI

9. TEMIS user workshop, Frascati, 8-9 October 2007 CH 2 O Vertical Columns Jan.2003 – Jun.2007 GOME CH 2 O VC averaged over 7 years (from 1996 to 2002) and the SCIAMACHY CH 2 O VC over the next 4 years and half (from 2003 to mid 2007). The general agreement between both instruments allows the generation of a combined long-term time series of CH 2 O vertical columns covering a full decade from 1997 until 2006. Apr.1996 – Dec.2001

10. TEMIS user workshop, Frascati, 8-9 October 2007 GOME – SCIAMACHY CH 2 O VCD [x10 16 mol/cm²] Jan. – Jun. 2003 CH 2 O Vertical Columns Over the 6 first months of 2003: General agreement within 7.5x10 15 mol/cm². SCIA is higher than GOME from 40° in latitudes N and S. South Atlantic Anomaly effect is different.

11. TEMIS user workshop, Frascati, 8-9 October 2007 CH 2 O Vertical Columns: America Good agreement over the six first months Stronger seasonal variability with SCIA. Very good agreement in South America Stronger SAA effect with SCIA

12. TEMIS user workshop, Frascati, 8-9 October 2007 CH 2 O Vertical Columns: Asia Good agreement over the six first months, SCIA a bit lower. Much stronger seasonal variability with SCIA. Very good agreement in biomass burning regions.

13. TEMIS user workshop, Frascati, 8-9 October 2007 CH 2 O Vertical Columns: Africa Very good overall agreement in Africa.

14. TEMIS user workshop, Frascati, 8-9 October 2007 Special Event: Greek Fires this Summer CH 2 O as measured by SCIA on 26 August 2007 superimposed over an image made by MODIS. Due to the strong north-easterly wind the smoke from the forest fires is blown all the way to the coast of Lybia.

15. TEMIS user workshop, Frascati, 8-9 October 2007 Total VCD Error Evaluation Vertical columns calculated from the slant columns (SC), air mass factors (AMF) and a zonal correction above Pacific Ocean (SC O and VC O ): As the determination of the SC, AMF and VC O are independent, the total error on the tropospheric vertical column can be expressed as: σ SC : error on the SC. Can be separated into its random and systematic part. σ AMF : error on the AMF evaluation. σ VC0 : error on the background correction above Pacific Ocean.

16. TEMIS user workshop, Frascati, 8-9 October 2007 Global Error Budget Total Error around 25%. At low and mid latitudes, AMF error dominates with the main contribution from clouds and profile shape uncertainties. At higher latitudes, SC error dominates because of higher Ozone concentrations. Monthly average allows to reduce SC random error.

17. TEMIS user workshop, Frascati, 8-9 October 2007 Users Modellers community: –IMAGES (J-F Muller and J. Stavrakou, BIRA-IASB, Brussels): current user, paper in preparation. –CHIMERE (G. Dufour, LISA, Paris): future user, data provided. –GEOS-CHEM (P. Palmer, Tropospheric Chemistry Earth Observation Modelling and Measurement Group, University of Edinburgh): other possible user. National and regional environmental protection agencies: –Europe: UBA-Austria, EMPA Switzerland and LANUV Northrhine-Westfalia: users within Promote. –China: National Satellite Meteorological Centre NSMC (Peng Zhang), Institute of Atmospheric Physics, CAS IAP-CAS (Pucai Wang): Contacts in China through the AMFIC project, can help to find users there.

18. TEMIS user workshop, Frascati, 8-9 October 2007 Conclusions and Outlook On the TEMIS website, you will find: –Daily, monthly and yearly maps for GOME and SCIAMACHY. –Data files with averaging kernels and error estimation for each satellite pixel. The dataset will be regularly extended with fresh SCIA data. The analysis of GOME-2 data will start within the next months. The global coverage in 1,5 day should allow to reduce the noise in the results. Consistency between the platforms needs to be evaluated regularly (changes in time) and validated with ground-based measurements that become more and more available for CH 2 O.

19. TEMIS user workshop, Frascati, 8-9 October 2007 Conclusions and Outlook The quality and the consistency of the data is very important to be able to detect possible trends in emissions. A derived product based on inverse modelling could be developed within TEMIS to provide constraints on VOC emissions. Possibilities of more users working on emission inventories (GFED, MEGAN).