1. Air Pollution/Environmental Technology laboratory Initial results on OMI NO 2 Validation during CINDI A contribution to the BIRA Cindi Workshop Yipin Zhou, Dominik Brunner, and Brigitte Buchmann Empa, Swiss Federal Laboratories for Materials Testing and Research Dübendorf, Switzerland Empa, Swiss Federal Laboratories for Materials Testing and Research Dübendorf, Switzerland With special thanks to Florence Goutail Folkert Boersma Katrijn Clemer BIRA

2. Air Pollution/Environmental Technology laboratory Outlook 1.Comparison of SAOZ NO 2 column with In-situ column calculated with Lidar and Ceilometer boundary height. 2.Introduction to Empa OMI NO 2 retrieval. 3.Comparison of OMI NO 2 column with SAOZ.

3. Air Pollution/Environmental Technology laboratory In-situ vs SAOZ NO 2 columns (10 mins resolution) LIDAR PBL tops 11 < UTC < 18 June 24th

4. Air Pollution/Environmental Technology laboratory Ceilometer PBL tops 11 < UTC < 18 In-situ vs SAOZ NO 2 columns (10 mins resolution)

5. Air Pollution/Environmental Technology laboratory In-situ vs SAOZ NO 2 columns (1 hour averages) 11 < UTC < 18

6. Air Pollution/Environmental Technology laboratory OMI tropospheric NO 2 retrieval 1.Based on DOMINO retrieval (TM4 a-priori, SCD, cloud algorithm) 2.Improved AMF calculation (high spatial resolution terrain height, considering BRDF effect based on high spatial and temporal resolution MODIS data set) 3.On-line calculation with LIDORT 3.3

7. Air Pollution/Environmental Technology laboratory SZA Surface reflectance generally depends on solar zenith angle (SZA) and viewing zenith angle (VZA) OMI tropospheric NO 2 retrieval f vol in July f vol in November volumetricgeometric

8. Air Pollution/Environmental Technology laboratory VZA BRF Example in summer (July) Typical OMI swath OMI tropospheric NO 2 retrieval Relative error in NO 2

9. Air Pollution/Environmental Technology laboratory OMI tropospheric NO 2 retrieval Mean NO 2 VTCs averaged over the years 2006 and 2007 (July, Nov)

10. Air Pollution/Environmental Technology laboratory OMI pixel selection For each orbit (VZA <65), find the pixel closest to the Cabauw tower. Average if there are two pixels with similiar distance.

11. Air Pollution/Environmental Technology laboratory Row anomaly (28 th -40 th,46 th -50 th,53 th -54 th pixels are affected ) Empa retrieval (screening, cloud fraction < 25%) OMI vs SAOZ

12. Air Pollution/Environmental Technology laboratory OMI vs SAOZ n=12 (only good pixels) n=20 (including row anomaly pixels) Cloud radiance fraction (cloud fraction < 25%)

13. Air Pollution/Environmental Technology laboratory OMI vs SAOZ Cloud screening is necessary for validation

14. Air Pollution/Environmental Technology laboratory Conclusions 1.NO 2 columns constructed from the in-situ measurement agrees well with the SAOZ columns. Better agreement is found from the in-situ columns calculated with boundary height from Lidar and SAOZ retrieved with IASB AMFs calculated using their NO 2 and aerosol profiles. 2.For the pixels with cloud fraction smaller than 25%, the correlation of the OMI NO 2 columns and the SAOZ columns are better than 0.6. Empa retrieval shows good agreement even when the sample size is quite small. Albedo effect is not obvious during this time period. 3.Cloud shows larger impact on the NO 2 retrieval than the row anomaly.