1. Satellite based versus traditional air pollution monitoring: Requirements, limitations, and chances Dominik Brunner, Christoph Hueglin, Christoph Zellweger, and Brigitte Buchmann Empa, Swiss Federal Laboratories for Materials Testing and Research Laboratory for Air Pollution and Environmental Technology 8600 Dübendorf, Switzerland

2. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 2  Traditional air pollution monitoring  Network concepts, regulations  Design and applications of Swiss National Air Pollution Monitoring Network NABEL  Satellites for air pollution monitoring?  Sufficient spatial resolution?  Sufficiently accurate?  How limiting is restriction to clear sky overpasses?  Analysis of hourly NABEL observations for clear and all skies  Comparison of frequency distributions, diurnal cycles, and interannual variability under clear and all skies  Conclusions Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

3. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 3 Monitoring networks Purpose:  Representative measurement of concentrations of all major (regulated) air pollutants relevant for human health, agriculture, ecosystems, and material degradation  Characterize existing and identify new potential threats  Monitor current pollution levels and long-term trends  Support for decision makers (warnings, control of success of air quality policy (short and long-term reduction measures) Requirements  Should cover full range of pollution levels from street level (human health) to remote locations (ecosystems)  Should represent the different regions of a country or region, e.g. north and south of the Alps, different altitude levels  Use reference measurement techniques, traceable to reference standards  High accuracy across network needed for reliable trend estimates and intercomparability  Reliable and simple continuous operation  Near real-time data availability Traditional air pollution monitoring Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

4. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 4 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 Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

5. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 5 NABEL Measurement Programme Air Pollution & Climate Change GAW Pollutants with limit value in the Swiss ordinance PM (PM10, PM2.5, PM1) mass, EC/OC, size distribution Greenhouse gases (CH 4, N 2 O, halocarbons, SF 6 ), VOCs Nitrogen Compouds (NH 3, NH 4 +, N 2 O, HNO 3 ) Meteo (p, T, RH, radiation, wind) Traffic parameter Auxiliary Parameters: EMEP / EU Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

6. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 6 Application: Characterization of air pollution based on NABEL sites NABEL: annual mean values 2004 Swiss Air Pollution Monitoring Network (NABEL)

7. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich Application: Monitoring of long-term trends, e.g. PM10 (annual means) Limit value annual limit values Switzerland 20 EU 2005 40 WHO, EU 2010 20 Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions Swiss Air Pollution Monitoring Network (NABEL)

8. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 8 Application: Independent control for emission reporting Country-by-country emissions reported to EMEP versus time evolution of observed concentrations Emissions per country Annual mean concentrations at urban stations and Jungfraujoch Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions Swiss Air Pollution Monitoring Network (NABEL) Nitrogen oxides (NO x ) All values normalized to 1997

9. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 9 Air pollution monitoring from satellites? PhD D. Schaub GOME (launch 1995) 320  40 km 2 SCIAMACHY (launch 2002) 60  40 km 2 Sufficient spatial resolution? Schaub, D. et al., Atmos. Chem. Phys. 5, 23-37, 2005 Schaub, D. et al., Atmos. Chem. Phys. 6, 3211-3229, 2006 Schaub, D. et al., Atmos. Chem. Phys. 7(23): 5971-5987, 2007 PhD Y. Zhou OMI (launch 2004) up to 24  13 km 2 Jan 2006 – July 2007 mean Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions Dispersion model Grid size 400  400 m 2

10. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 10 Ground-based columns using averaging kernel information (see Schaub et al., 2006) OMI NO 2 VTCs vs. ground-based NO 2 VTCs All data points: r = 0.82 Precision of better than 1 x 10 15 molec cm -3 highly desired Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions Air pollution monitoring from satellites? Sufficiently accurate?

11. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 11 Limitations of clear-sky observations 1. Frequency distributions of hourly means Bern, urban kerbside Payerne, rural Zurich, urban background Significant undersampling of polluted situations if restricted to clear-sky observations at urban background and rural sites Annual mean limit mean values 95% percentiles Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

12. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 12 Limitations of clear-sky observations 2. Annual average diurnal cycles -Evening traffic peak is missed during most time of the year if restricted to daytime observations -Surface level NO 2 is increased in the morning and decreased in the evening on clear-sky days daytime only daytime clear sky only All observations Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions 11 hrs 13 hrs

13. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 13 Limitations of clear-sky observations 3. Interannual variability of annual means -Annual mean values are significantly reduced if restricted to OMI clear sky overpasses -But: interannual variability reasonably well captured All observations OMI clear sky overpasses only Daytime clear sky only Annual mean limit Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions

14. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 14 Limitations of clear-sky observations 3. Interannual variability - About 70% of variance in annual means captured with clear sky sampling -Reduced to 60% if restricted to OMI overpasses -Still 50-60% of variability in extremes captured Correlations between annual means/percentiles of subsamples and full annual means Annual means 95% percentiles Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions All stations urban rural

15. 50km N Basel Bern Chaumont Davos Dübendorf Härkingen Jungfraujo ch Lägeren Lausanne Lugano Magadino Payerne Rigi Sion Tänikon Zürich 15  Air quality monitoring requires high spatial resolution (exposures, critical loads)  Reliable long-term trends important for policy control -> continuity in satellite missions required -> large resolution and design changes from instrument to instrument causes some problems  Comparison with in-situ observations quite satisfactory  precision of better than 1 x 10 15 molec/cm 3 NO 2 highly desired  Clear-sky observations is a significant limitation for extremes (in Switzerland) but less so for interannual and long-term variations.  Good boundary layer scheme mandatory for a-priori NO 2 profiles  Spatially resolved reliable long-term trends is probably the most exciting (air quality) product from satellites so far  Models add a lot to the value of satellite missions Conclusions for TROPOMI mission Outline Traditional monitoring Air pollution monitoring using satellites? Limitations of clear-sky overpasses Conclusions