1.  Methodology  Comparison with others instruments  Impact of daily AMF  Conclusions Tropospheric NO 2 from SAOZ F. Goutail, A. Pazmino, A. Griesfeller, D. Ionov LATMOS,CNRS/INSU, France OUTLINE Acknowledgements: Katrijn & Michel for MAXDOAS/IASB data Team from RIVM for In Situ data KNMI people for Boundary Layer Heights

2. Step 1: Calculate stratospheric column of the day  measurements at 90°-91°SZA (to limit pollution influence)  stratospheric NO2 AMF calculated with Sarkissian model for mid-lat single profile in summer Step 2: Remove the stratospheric content of each measurement  NO2 stratospheric diurnal variation considered Step 3: Calculate tropospheric column  3a Multiple scattering correction (using O4)  3b Column calculated using NO2 tropospheric AMF  3c Selection to SZA<82° Methodology

3. Clean day Very limited multiple scattering O4 slant columns better agreement with simulated using Urban aerosols! Overcast day Multiple scattering O4 slant columns larger than simulated -> use O 4 to take multiple scattering into account correction coef = O4 measured/O4 modeled Step 3a: Correction of multiple scattering from lower layers Methodology using SCIATRAN model

4. Step 3a: Correction of multiple scattering from lower layers Methodology Correction needed on overcast days

5. Comparison with others instruments Comparison between various instruments results  SAOZ zenith sky tropospheric columns using a tropospheric AMF Two tropospheric AMF have been tested (Step 3b)  Single AMF for the whole campaign using SCIATRAN NO2 and aerosols simulated profiles for June/July Mid-latitudes (Urban case)  Daily AMF calculated by IASB/BIRA using their MAXDOAS NO2 and aerosols measured profiles  MAXDOAS Integrated profiles in the troposphere  In Situ measurements (at 3m) converted to tropospheric column by considering homogeneous distribution in the boundary layer and using Boundary Layer Height of KNMI’s Ceilometer with best quality (3 & 4) Tropospheric NO2 columns

6. Comparison with others instruments => In Situ measurements converted to tropospheric column by considering homogeneous distribution in the BL and using BLH of KNMI’s ceilometer with best quality (3 & 4)  Similar daily evolution  Peaks are well reproduced from three instruments  Discrepancies SAOZ and in-situ / MAXDOAS at SZA>50° ->use of single AMF? Tropospheric NO2 columns use of calculated AMF using MAXDOAS profil (IASB team) 24/06/200925/06/2009

7. Impact of daily AMF Tropospheric NO2 columns 24/06/200925/06/2009

8. Tropospheric NO2 columns  Large improvement of SAOZ data compared to In-situ when using daily tropospheric IASB AMF, specially at SZA>50°  Improvement not significant around noon (SZA<50°) Impact of daily AMF 24/06/200925/06/2009

9. Tropospheric NO2 columns  Similar results for other days and different cases of NO2  Good agreement between instruments around noon => daily variability well reproduced  At SZA>50° - better agreement between In-situ and SAOZ using IASB daily AMF -MAXDOAS Integrated profiles sometimes overestimated. Impact of daily AMF 29/06/200930/06/2009

10. Conclusions  Intercomparison of three different instruments to crosscheck the tropospheric NO2 vertical columns  The use of Ceilometer boundary layer height allows to “convert” In-situ mixing ratio into vertical columns.  In general, good agreement between SAOZ, MAXDOAS/IASB & IN SITU/RIVM for different days Daily evolution and peaks are well reproduced and observed by the three instruments  Daily NO2 AMF calculated from MAXDOAS profiles improve significantly SAOZ data at SZA>50  Future: check others days and compare with others instruments (next step EGU, Vienna)