1. Quantitative retrievals of NO 2 from GOME Lara Gunn 1, Martyn Chipperfield 1, Richard Siddans 2 and Brian Kerridge 2 School of Earth and Environment Institute of Atmospheric Sciences 1. University of Leeds 2. Rutherford Appleton Laboratory

2. Introduction NO 2 from GOME has been widely studied Still the potential for a more accurate retrieval  Constrain the stratosphere (Chemical Data Assimialtion)  Use cloud and aerosol data from ATSR-2 (GRAPE) School of Earth and Environment Institute of Atmospheric Sciences

3. Input Parameters (Atmospheric Profiles, GRAPE and GOME snr and slant columns) Radiative Transfer Model (Calculates Photon Path Lengths) Retrieval Model Optimal Estimation Calculate slant column and surface albedo Estimate of scaling factor and albedo New estimate of scaling factor and albedo Output (Tropospheric VCD, errors)

4. Input Parameters Atmospheric Profiles Stratosphere Troposphere

5. SLIMCAT 3D CTM with chemical data assimilation of long-lived species. Data Assimilation from 1992 on of HALOE CH 4, O 3, HCl, H 2 O. Detailed stratospheric chemistry scheme including heterogeneous reactions. 7.5 o x 7.5 o x 24 levels (surface - 60km) Forced using 6-hourly L60 ECMWF analyses (ERA-40 until 2001) Stratosphere

6. Troposphere TOMCAT monthly mean profiles Off-line tropospheric chemistry model forced by ECMWF winds 64 longitudes 32 latitudes (T21) grid over 31 levels Model description see Arnold et al. 2005

7. Input Parameters GRAPE

8. Cloud and Aerosol Data (GRAPE) GRAPE Global Retrieval of ATSR cloud Parameters and Evaluation (NERC – RAL – Oxford) State-of-the-art retrieval for the whole ATSR2 dataset. Cloud optical depth, height, temperature and aerosol particle size, type, optical depth

9. Input Parameters GOME sun normalised radiance GOME slant columns - gdp and sao

10. Input Parameters (Atmospheric Profiles, GRAPE and GOME snr and sc) Radiative Transfer Model (Calculates Photon Path Lengths) Retrieval Model (Dual) Optimal Estimation Calculate slant column and surface albedo Estimate of scaling factor and albedo New estimate of scaling factor and albedo Output (Tropospheric VCD, errors)

11. Retrieval Model Optimal Estimation theory x i – state vector [scaling factor, albedo] y – measurement vector [slant column, sun normalised radiance] x i+1 =x i +(S E -1 +K i T S E -1 K i ) -1 [K i T S E -1 (y-F(x i ))-S a -1 (x i -x a )]

12. Input Parameters (Atmospheric Profiles, GRAPE and GOME albedo) Radiative Transfer Model (Calculates Photon Path Lengths) Retrieval Model Optimal Estimation Calculate slant column and surface albedo Estimate of scaling factor and albedo New estimate of scaling factor and albedo Output (Tropospheric VCD, errors)

13. Radiative Transfer Code Optimized version of GOMETRAN Scattering cross sections, atmospheric profiles Phase functions are calculated at Oxford Simulates spectrum of radiance received by GOME Calculates ‘weighting functions’ (derivatives with respect to the parameters retrieved) Clouds as a scattering layer

14. Input Parameters (Atmospheric Profiles, GRAPE and GOME snr / sc) Radiative Transfer Model (Calculates Photon Path Lengths) Retrieval Model (Dual) Optimal Estimation Calculate slant column and surface albedo Estimate of scaling factor and albedo New estimate of scaling factor and albedo Output (Tropospheric VCD, errors)

15. Output

16. 1.Show NO2 enhancements where excepted 2.Background values are strongly negative 3.Maybe due to profiles used in model

17. 69 1.Show NO2 enhanceme nts where excepted 2.Background values are strongly negative 3.Concs are too high 4.Why are there bits missing???

18. Problems Stratosphere

19. Two Experiments –Free running model –Model constrained by chemical data assimilation of 4 species (CH 4, HCl, H 2 O and O 3 ) Sequential sub optimal Kalman filter is used to assimilate HALOE observations of CH 4, H 2 O, O 3 and HCl. Species are constrained by conservation of compact correlations in the model (references Khattatov et al 2002, Chipperfield et al 2003) latitude CH 4 Assimilation (Run B) CH 4 Free running (Run A) ppbv Pressure (hPa) Assimilated winds (here ERA-40) known to cause too much horizontal mixing causing age of age to be too old (Schoeberl et al, 2003) Gradients in the subtropics have increased

20. How does assimilation of a single long-lived tracer (CH 4 ) and O 3 lead to improvements in modelled NO 2 ? N 2 O is altered due to the preservation of its compact correlation with CH 4 NOy is altered through compact NOy:N2O correlation. NOy is partitioned into the component species by model chemistry. Changed O 3 (assimilation) also affects NOy partitioning (e.g. NO:NO 2 ratio) Assimilation Scheme

21. Short-lived Species Validation NO 2 vmr (ppbv) Pressure (hPa) Key Obs Run A Run B ATMOS 3 SS100 10.3 N 16.3 W ATMOS 3 SR49 71.1 S 150.3 E

22. Problems Retrieval Model

23. Conclusions – Future work NO 2 tropospheric VCD background negative NO 2 tropospheric VCD are too high Stratospheric column calculation could be to blame! Correct the stratosphere Quantify the errors