1. Ankie Piters Royal Netherlands Meteorological Institute Ministry of Infrastructure and Environment Measuring vertical profiles and tropospheric columns of NO 2 photo: A. Apituley photo: T. Vlemmix

2. Atmospheric Composition Research Main Scientific Themes: ozone layer, air quality, and chemistry-climate interaction Division: 76 people (of which ~40 on OMI/TROPOMI - PI) Observation group: Satellite observations: retrieval, validation and distribution of data. OMI, TROPOMI/S5p, GOME, SCIAMACHY, GOME-2, SEVIRI. Main products: O 3, NO 2, aerosols, clouds Ground-based measurements important for satellite and model validation Modelling group: Coupling TM5 to EC Earth, focus: aerosols and non-CO 2 GHG Air quality forecasts Data assimilation

3. Ground-based measurements of O 3 and NO 2 operational measurements ozonesondes in De Bilt since 1992 ozonesondes in Paramaribo (Surinam) since 1999 Brewer (O 3 column) in De Bilt and Paramaribo (1994/1999) 2 MAX-DOAS (trop NO 2 ) in De Bilt/Cabauw (2008) participation in global networks: GAW/WOUDC, SHADOZ, NDACC instrument development: NO 2 sonde development since 2008 campaigns in Cabauw (focus NO 2 ) DANDELIONS 2005 & 2006 CINDI 2009 PEGASOS, 2012 other campaigns (with NO 2 sonde) DISCOVER-AQ, Washington/Baltimore, 2011 ACTRIS, Hohenpeissenberg, 2012 DISCOVER-AQ, California, Jan-Feb 2013 VOGA-NCP, Beijing area, June 2013

4. MAX-DOAS side-by-side intercomparison: 4 sondes + 2 NOx analysers NO2 sonde preparation

5. Cabauw – increasing satellite validation potential (chemistry) Cabauw: Tropospheric air representative for satellite pixel sizes Wide range of pollution levels, no local sources nearby (except for farms!) Vertical information (tropospheric columns) with remote sensing instruments, complemented with in-situ on site and in tower. Gases of interest: O 3, NO 2, CO 2, AOD, CO, CH 4, HCHO, H 2 O and SO 2 Long-term goals Organise campaigns for satellite validation Maintain current operational NO 2 measurements Increase potential of Cabauw with an FTS instrument measuring vertical columns and profiles of GHG (together with ECN) picture: Ronald van der A, KNMI global NO 2 distribution based on OMI data

6. FTIR visit in Cabauw Mobile FTIR from BIRA Columns and profiles of CH 4, CO, and N 2 O between May and July 2013 (PEGASOS and INGOS) CO N2O CH4

7. MAX-DOAS spectrum of scattered sunlight at different elevation angles tropospheric NO 2 from differential absorption w.r.t. zenith (strat. NO 2 )

8. Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments overview: Piters et al, AMT, 2012 Wittrock et al., in prep., AMT Photo: M. Kroon

9. MAX-DOAS tropospheric NO 2 compared to OMI Vlemmix et al, AMT, 2010 When aerosol correction applied: no sign. bias between OMI and MAX- DOAS σ GB < 30% : R=0.64 (grey) σ GB < 20% : R=0.73 (black) σ GB < 10% : R=0.88 (red) Spread larger than expected from retrieval errors alone. Difference in spatial representativity

10. Use of MAX-DOAS data in model verification Average trop NO2 for different wind directions (5. 10 15 molec cm -2 per circle) National Air Quality Model Lotos-Euros Sunday Vlemmix et al., ACPD 2012 measurements from De Bilt

11. The NO 2 sonde -Measures high resolution NO 2 profiles -Light weight -Low power consumption -Can be launched on small weather balloon Idea: Wesley Sluis Design: Marc Allaart Chemistry: Mirjam den Hoed

12. The NO 2 profiles up to ~10km (balloon burst) two profiles for each launch (‘up’ and ‘down’) large variability in shapes Winter 2010-2011

13. sonde on tethered balloon: -build up of boundary layer -development of detailed structures

14. Measurement principle based on chemiluminescent reaction of NO 2 with luminol photons are detected with photodiode array electronics: converts femto-amperes to millivolts luminol reservoir prevents acidification by CO 2 Sluis et al., AMT, 2010

15. NO 2 variations are very well captured. RMS difference is <10% absolute calibration still to be optimized (here: constant scaling factors applied) How accurate can we measure NO2?

16. Demonstration for OMI NO 2 validation Red: a priori (model) profile used for satellite retrievals Black: NO 2 sonde profile Difference in profile shape results in errors up to 50% in satellite NO 2 21 May 2012 error: ~5% 22 May 2012 error: ~50% Piters et al., ACVE, 2013

17. Comparing with AQ models Thanks to: Henk Eskes and Patricia Castellanos, KNMI

18. Modeled NO 2 above boundary layer 24h backtrajectory at 1km height = measured air mass The Lotos-Euros model shows: NO 2 vertical transport to the free troposphere Horizontal transport of free tropospheric NO 2 Possible origin of difference with sonde: Life time of NO 2 Vertical/horizontal transport Surface emissions 1km, start of back-trajectory BL (model)

19. Weather balloon NOx analysers RIVM/LML Photo: A. Apituley PEGASOS campaign May 2012, Cabauw (only NO 2 instruments are shown) zeppelin Marc and Ankie with NO2 sondes NOx analyser @200m RIVM NO2 lidar RIVM mobile lab (Juelich) MAX-DOAS (2x)

20. 500 m 6:00 7:00 8:30 9:45 EURAD model (Univ. Cologne) 1200 m 0 m 27-5-2012 NO 2 concentration (arbitrary offset and scaling)

21. Future plans... Optimisation of the calibration Optimisation of the design Transfer knowledge to industry for serial production Use it for the validation of models, MAXDOAS and indirectly of satellites Marc and Deborah recovering a sonde Photo: A. Apituley