1. A comparison of OMI NO 2 VTC with in- situ measurements in Switzerland Dominik Brunner, Brigitte Buchmann, Thomas Seitz, and Martin Steinbacher Empa, Swiss Federal Laboratories for Materials Testing and Research Laboratory for Air Pollution and Environmental Technology 8600 Dübendorf, Switzerland Thanks to Folkert Boersma and Ruud Dirksen (KNMI) for creating the post-analysis near-real time (PA-NRT) OMI data and providing it through TEMIS

2. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 2  Motivation  The NABEL air quality monitoring network in Switzerland  NO x and NO 2 trends since 1980s  Measurements with conventional NO x sensors  Lessons from parallel operation of molybdenum & photolytic converters  Comparison with in situ NO 2 measurements  NO 2 (m) = NO x (molybdenum) - NO  NO 2 (c ) = NO 2 (m) corrected for interferences  Comparison with ground-based NO 2 columns  Measurement stations and method used for computation of columns  Direct comparison with columns integrated over profile  Comparison with averaging kernel weighted columns  Conclusions and outlook Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

3. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 3 Urban, near street Rural < 1000 m amsl Urban, in park Rural > 1000 m amsl Motorway Prealpine, forest Agglomeration Alpine Swiss Air Pollution Monitoring Network (NABEL) Air Pollution/Environmental Technology 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujoch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

4. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 4 Assessment of Swiss Air Pollution Policy Swiss National Air Pollution Monitoring Network (NABEL) sulphur dioxide (SO 2 ) nitrogen dioxide (NO 2 ) NABEL measurement station Zurich downtown city background Additional reduction measures needed Air Pollution reduction measures successful Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

5. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 5 Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

6. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 6 NO 2 measurements using conventional NO x sensors with Molybdenum converters PAN Mean annual NO 2 cycles ruralpre-alpine Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

7. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 7 SCIA OMI ~60% high in spring/summer ~20% high in autumn/winter rural pre-alpine NO 2 measurements using conventional NO x sensors with Molybdenum converters Mean diurnal cycles Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

8. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 8 OMI NO 2 VTCs vs. ground-based NO 2 Selection of OMI pixels for given NABEL measurement stations Payerne (rural) Tänikon (rural) Dübendorf (sub-urban) Swiss high-resolution NO x inventory Zurich Bern Basel Geneva Swiss alps Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

9. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 9 OMI NO 2 VTCs vs. ground-based NO 2 Daily hourly mean 12-13 UTC (13-14 LT) values at Tänikon used for comparison with OMI NO 2 (m), molybdenum converter NO 2 (c), corrected (Steinbacher et al., 2007) Clear sky according to both OMI and ground Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

10. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 10 OMI NO 2 VTCs vs. ground-based NO 2 Fractional cloud cover of OMI pixels over Tänikon Fractional cloud cover Temperature at Tänikon Points identified as clear sky based on global radiation sensor at Tänikon Snow cover Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

11. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 11 NO 2 (m) Direct comparison with volume mixing ratios measured in-situ at Tänikon OMI NO 2 VTCs vs. ground-based NO 2 Corrected NO 2 (c) NO 2 (c) [ppb] NO 2 (m) [ppb] Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

12. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 12 Construction of vertical profiles and VTCs at Tänikon and Payerne from ground based observations at different altitudes OMI NO 2 VTCs vs. ground-based NO 2 VTCs 50km Chaumont Jungfraujoch Lägeren Payerne Rigi Tänikon Combination of measurements at Tänikon539 m amsl Lägeren689 m Rigi1013 m Chaumont1137 m Jungfraujoch3650 m NO 2 (m) at Tänikon vs. Lägeren NO 2 (m) at Chaumont vs. Rigi r=0.89 r=0.75 Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

13. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 13 Selected NO 2 profiles above Tänikon reconstructed from ground-based corrected NO 2 (c) measurements OMI NO 2 VTCs vs. ground-based NO 2 VTCs Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook Winter (28. Jan 2006)Summer (18. Aug 2006) Tänikon Lägeren Rigi and Chaumont Jungfraujoch

14. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 14 Direct comparison without using averaging kernels OMI NO 2 VTCs vs. ground-based NO 2 VTCs Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

15. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 15 Ground-based columns using averaging kernels (see Schaub et al., 2006) OMI NO 2 VTCs vs. ground-based NO 2 VTCs Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook

16. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 16  NABEL in situ measurements from different stations at different elevations combined to construct vertical profiles  Conventional NO x measurements need correction  Comparison of OMI VTCs with in situ NO 2 VMR shows reasonable to good agreement except for summer  No improvement when using corrected NO 2 (c)  Comparison of OMI VTCs with ground-based reconstructed VTCs shows better agreement than comparison with NO 2 VMR  Using averaging kernels significantly improves agreement between OMI VTCs and reconstructed VTCs  Future: Use photolytic converter measurements at Payerne and Rigi, extend data set to 2007, new OMI data version, try to assess uncertainty of ground-based columns Summary and outlook Outline Motivation NABEL NO x trends NO x sensors Comparison in-situ NO 2 NO 2 (m) NO 2 (c) Comparison to columns Method Direct Avg. kernel Conclusions & Outlook