1. Hester Volten, Ellen Brinksma, Stijn Berkhout, Daan Swart, René van der Hoff, Hans Bergwerff, Pieternel Levelt, Gaia Pinardi, Michel Van Roozendael NO 2 lidar profiles measured during the DANDELIONS validation campaign 2006

2. “How representative is an OMI measurement for surface concentrations?” DANDELIONS Sept. 2006 – Objectives O 3 : total column and profile (sondes) tropospheric contribution NO 2 : lower tropospheric profile (lidar) total columns (focus: pollution) MAXDOAS intercomparison Aerosol:radiosondes, CIMEL, SPUV, aethalometer CESAR site (Cabauw, 51.971°N, 4.927°E) many continuous measurements full meteorological info at location 2007 research questions (for NO 2 ): 1)Shape of NO 2 profiles (and influence on OMINO2) for industrial area 2) Homogeneity of the NO 2 field Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY Cabauw industry Clean air CESAR industry

3. Participating Institutes and Instruments OMI, SCIAMACHY RIVMNO 2 lidar, NO 2 in-situ monitors, boundary layer lidar BIRA-IASBMAXDOAS, Mini MAXDOAS IUP HeidelbergMAXDOAS (three directions) IUP BremenMAXDOAS NASA-GSFC Direct Sun Instrument (Pandora) KNMI Mini MAXDOAS, ozone sondes, radio sondes TNOSun photometers, volatility system, aethalometer, nephelometer, etc. Nine validation days on Sept 8-13, 20-22 Data publicly available on AVDC http://avdc.gsfc.nasa.gov

4. The third dimension : NO 2 lidar – ground level to about 2.5 km NO 2 in-situ monitor - on the ground and at 200 m Mini MAXDOAS - on the mast (200m)

5. Mobile NO 2 Lidar telescope Rapid switching between two wavelengths

6. How to Measure a Profile 300 m

7. NO 2 Lidar Measurements during the DANDELIONS campaign NO 2 profiles during overpasses – seven different elevations 0.75, 1.5, 3, 6, 12, 24, 90 deg, 1 azimuth (39 degrees) Spatial variations – two azimuths (39 and -36 deg), 1 elevation (12 degrees) Time variations – 1 azimuth (39 degrees), 1 elevation (12 degrees), long time series EXAMPLE: 12 SEPTEMBER in-situ monitor comparison Mini MAXDOAS heterogeneity

8. Overview of all NO2 lidar measurements September 2006 Profile assumed in OMI retrieval concentration NO 2 (  g/m 3 ) 500 10 20 3040 500 1000 1500 60 Altitude (m) Profile shape influences OMI retrieval

9. OMI L4 tropospheric columns 12 September-polluted day

10. NO 2 lidar profile compares well with in-situ data

11. 0,1,2,3,4,5,6,8,10, 12,14,16,20,25,30 -10,-8,-6,-4,-3,-2,-1 Example Mini MAXDOAS measurement High sensitivity to the vertical NO 2 distribution in the lowest 200 m Zenith Julian day

12. Boundary layer growth NO 2 layer below 200 m NO 2 layer above 200 m

13. NO 2 lidar profile compares badly with in-situ data OMI overpass 12:47 UT

14. Heterogeneity on 12 September NO 2 lidar - different azimuth angles elevation 12 deg

15. Heterogeneity on 12 September NO 2 lidar - time series elevation 12 deg

16. Lidar values smaller or the same as in-situ values No problem Problem !

17. Lidar versus in-situ NH 3 interference in-situ monitors? No solution: Error through NH3 interference cannot be larger than 6%

18. Conclusions We had a hugely successful DANDELIONS campaign in 2006. Data is available on AVDC. NO 2 lidar profile shapes differ quite a lot from OMI assumption Concentrations on clear and polluted days show large variations, from ~3 to ~50  g/m 3 Heterogeneity in space and time is sometimes very large In-situ data and lidar data do not always agree