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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.

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  1. A comparison of OMI NO2 VTC with in-situ measurements in SwitzerlandDominik Brunner, Brigitte Buchmann,Thomas Seitz, and Martin SteinbacherEmpa, Swiss Federal Laboratories for Materials Testing and Research Laboratory for Air Pollution and Environmental Technology8600 Dübendorf, Switzerland Thanks to Folkert Boersma and Ruud Dirksen (KNMI)for creating the post-analysis near-real time (PA-NRT) OMI dataand providing it through TEMIS

  2. Outline • Motivation • The NABEL air quality monitoring network in Switzerland • NOx and NO2 trends since 1980s • Measurements with conventional NOx sensors • Lessons from parallel operation of molybdenum & photolytic converters • Comparison with in situ NO2 measurements • NO2(m) = NOx (molybdenum) - NO • NO2(c ) = NO2(m) corrected for interferences • Comparison with ground-based NO2 columns • Measurement stations and method used for computationof columns • Direct comparison with columns integrated over profile • Comparison with averaging kernel weighted columns • Conclusions and outlook Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook

  3. Swiss AirPollution Monitoring Network (NABEL) Lägeren Tänikon Basel Dübendorf Zürich Härkingen Chaumont Rigi Bern Payerne Davos Lausanne Jungfraujoch Magadino Sion 50km Lugano N Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook Urban, near street Rural < 1000 m amsl Urban, in park Rural > 1000 m amsl Motorway Prealpine, forest Agglomeration Alpine Air Pollution/Environmental Technology

  4. Assessment of Swiss Air Pollution Policy Swiss National Air Pollution Monitoring Network (NABEL) 70 60 50 40 3 µg/m Limit value 30 20 10 0 1980 1985 1990 1995 2000 NABEL measurement station Zurich downtowncity background Outline MotivationNABELNOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook nitrogen dioxide (NO2) Additional reduction measures needed Air Pollution reduction measures successful sulphur dioxide(SO2)

  5. Outline MotivationNABELNOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook

  6. NO2 measurements using conventional NOx sensors with Molybdenum converters Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook Mean annual NO2 cycles rural pre-alpine PAN

  7. NO2 measurements using conventional NOx sensors with Molybdenum converters Mean diurnal cycles rural OMI SCIA ~60% high inspring/summer Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook ~20% high inautumn/winter pre-alpine

  8. OMI NO2 VTCs vs. ground-based NO2 Selection of OMI pixels for given NABEL measurement stations Swiss high-resolution NOx inventory Basel Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook Zurich Bern Swiss alps Tänikon (rural) Geneva Dübendorf (sub-urban) Payerne (rural)

  9. OMI NO2 VTCs vs. ground-based NO2 Daily hourly mean 12-13 UTC (13-14 LT) values at Tänikon used for comparison with OMI Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook NO2(m), molybdenum converter NO2(c), corrected (Steinbacher et al., 2007) Clear sky according to both OMI and ground

  10. Snow cover OMI NO2 VTCs vs. ground-based NO2 Fractional cloud cover of OMI pixels over Tänikon Points identified as clear sky basedon global radiation sensor at Tänikon Fractional cloud cover Temperature at Tänikon Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook

  11. OMI NO2 VTCs vs. ground-based NO2 Direct comparison with volume mixing ratios measured in-situ at Tänikon Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook Corrected NO2(c) NO2(m) NO2(c) [ppb] NO2(m) [ppb]

  12. Lägeren Tänikon Chaumont Rigi Payerne Jungfraujoch 50km OMI NO2 VTCs vs. ground-based NO2 VTCs Construction of vertical profiles and VTCs at Tänikon and Payernefrom ground based observations at different altitudes Combination of measurements atTänikon 539 m amsl Lägeren 689 m Rigi 1013 m Chaumont 1137 m Jungfraujoch 3650 m Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columnsMethod Direct Avg. kernel Conclusions& Outlook NO2(m) at Chaumont vs. Rigi NO2(m) at Tänikon vs. Lägeren r=0.89 r=0.75

  13. OMI NO2 VTCs vs. ground-based NO2 VTCs Selected NO2 profiles above Tänikon reconstructed from ground-based corrected NO2(c) measurements Winter (28. Jan 2006) Summer (18. Aug 2006) Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columnsMethod Direct Avg. kernel Conclusions& Outlook Jungfraujoch Rigi and Chaumont Lägeren Tänikon

  14. OMI NO2 VTCs vs. ground-based NO2 VTCs Direct comparison without using averaging kernels Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns MethodDirect Avg. kernel Conclusions& Outlook

  15. OMI NO2 VTCs vs. ground-based NO2 VTCs Ground-based columns using averaging kernels (see Schaub et al., 2006) Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method DirectAvg. kernel Conclusions& Outlook

  16. Summary and outlook • NABEL in situ measurements from different stations at different elevations combined to construct vertical profiles • Conventional NOx measurements need correction • Comparison of OMI VTCs with in situ NO2 VMR shows reasonable to good agreement except for summer • No improvement when using corrected NO2(c) • Comparison of OMI VTCs with ground-based reconstructed VTCs shows better agreement than comparison with NO2 VMR • Using averaging kernels significantly improves agreementbetween OMI VTCs and reconstructed VTCs • Future: Use photolytic converter measurements at Payerne andRigi, extend data set to 2007, new OMI data version, try toassess uncertainty of ground-based columns Outline MotivationNABEL NOx trends NOx sensors Comparisonin-situ NO2 NO2(m) NO2(c) Comparisonto columns Method Direct Avg. kernel Conclusions& Outlook

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