AMFIC second progress meeting MariLiza Koukouli & Dimitris Balis Laboratory of Atmospheric Physics Aristotle University of Thessaloniki

Task 3.1: Validation of satellite-retrieved aerosol properties over a wide range of geolocations over Europe and China using ground-based results from the AERONET network. Task 3.2: Validation of satellite-retrieved aerosol properties over the city of Thessaloniki using a dedicated ground-based Brewer spectrophotometer. Task 3.3: Validation of satellite-retrieved SO 2 pollution fields over a wide range of geolocations over Europe and China where ground- based Brewer spectrophotometers exist. Task 3.4: Validation of the satellite-retrieved SO 2 pollution fields over the city of Thessaloniki using the coincident to the satellite overpass ground-based Brewer spectrophotometers measurements. Task 3.5: Validation of satellite-retrieved tropospheric O 3 slant columns over selected Chinese and European stations that include ozone sondes. Work package 3: Validation of aerosol properties, SO 2 and O 3 amounts

Task 3.1: Validation of satellite-retrieved aerosol properties over a wide range of geolocations over Europe and China using ground-based results from the AERONET network. Task 3.2: Validation of satellite-retrieved aerosol properties over the city of Thessaloniki using a dedicated ground-based Brewer spectrophotometer. Task 3.3: Validation of satellite-retrieved SO 2 pollution fields over a wide range of geolocations over Europe and China where ground- based Brewer spectrophotometers exist. Task 3.4: Validation of the satellite-retrieved SO 2 pollution fields over the city of Thessaloniki using the coincident to the satellite overpass ground-based Brewer spectrophotometers measurements. Task 3.5: Validation of satellite-retrieved tropospheric O 3 slant columns over selected Chinese and European stations that include ozone sondes.

The SO 2 issue over Europe

The SO 2 issue over China

Brewer SO 2 data  From the original 84 stations that provide total DAILY SO 2 columns in after cleaning up rogue files and keeping only data from year 2000 onwards, some 58 global stations remain.  Keeping only those stations with coincident measurements with the Sciamachy/OMI overpasses between 2004 and 2007 in Europe and China we are left with some 24 stations in total. We are not given the standard deviation of the daily SO 2 Brewer measurements

Brewer SO 2 data  For Thessaloniki we have direct access to the measurements including the nominal measuring period during the day from which the daily values are extracted.

Limitations of the Brewer SO 2 measurements Brewers measure UV at five wavelengths, four longer wavelengths are used to derive ozone, the fifth (shortest) wavelength is used only for SO 2. There are several sources of errors in Brewer SO 2 measurements:  Stray light. Since SO 2 measurements are based on the shortest wavelength signal, these measurements are strongly affected by stray light i.e. by light that is actually coming from longer wavelengths. That causes errors in SO 2 at high zenith angles and under high total ozone conditions. SO 2 can be negative due to this problem.  The ExtraTerrestrialConstant errors. Unlike ozone, it is difficult to determine ETC for SO 2 from a comparison with a standard instrument. A generic ETC value is used instead. This yield an error that depends on the solar zenith angle. The error is high when the solar zenith angle is low. Vitali Fioletov, private communication

Limitations of the Brewer SO 2 measurements  Wavelength/absorption coefficient. The Brewer wavelength and the instrument sensitivity are not exactly the same for all instruments. Errors in effective SO 2 absorption coefficient introduces a bias, while wavelength shifts affect also the ETC causing more complicated errors. So, errors in SO 2 measurements are rather large and complicated. Present SO 2 algorithms might not be suitable for estimation of "background" SO 2 levels. Vitali Fioletov, private communication

Sciamachy SO 2 data  Overpass files within 50 km of centre given  In case of multiple satellite measurements in one day, the closest to the locus is chosen.  Three SO 2 total column density with plume height at: 1km 6km 14km  Successful AMF calculation [AQI=0] data kept  No restriction on cloud fraction as of yet.

OMI SO 2 data  Overpass files within 50 km of centre downloaded from  In case of multiple satellite measurements in one day, the closest to the locus is chosen. [i.e. no averaging performed so far.]  Only keeping data with cloud fraction less than 0.20

OMI SO 2 data  Four SO 2 total columns Planetary Boundary Layer (PBL) corresponding to CMA of 0.9 km. Lower tropospheric Layer (TRL) corresponding to CMA of 2.5 km. Middle tropospheric Layer (TRM) usually produced by volcanic degassing, corresponding to CMA of 7.5 km. Upper tropospheric and Stratospheric SO2 Layer (STL) usually produced by explosive volcanic eruption, corresponding to CMA of 17 km.

How the analysis is performed: per ground-based Brewer station  Raw differences [in DU]  Monthly differences  Monthly time series  Histogram representation  Scatter plot for the entire dataset For summer [Mar – Oct] For winter [Nov – Feb]  Seasonal [monthly] variability  Seasonal solar zenith angle dependence

Where we left of with the SO 2 last May 1. Calibration of Thessaloniki Brewer SO 2 dataset 2. Use, for Thessaloniki, the raw Brewer measurements instead of the daily mean value. Correlate better in time with the satellite data. 3. Examine the effect of constraining the Sciamachy SO2 data for SZA <75 deg [suggested by Jos] and to a cloud fraction < Examine the effect of constraining the OMI SO2 data for SZA <60 deg and to a cross-track position 10 to 50 [as suggested by Nick Krotkov]. 5. Instead of keeping the closest satellite measurements to the ground-position, do an average of all measurements of that day and present the daily variability.

Task 3.4: Validation of the Sciamachy & OMI SO 2 over the city of Thessaloniki

Task 3.4: Validation of the Sciamachy SO 2 over the city of Thessaloniki, 1km

Task 3.4: Validation of the Sciamachy SO 2 over the city of Thessaloniki, 6km

Task 3.4: Validation of the Sciamachy SO 2 over the city of Thessaloniki

Task 3.4: Discussion of the Thessaloniki Brewer total SO 2 : corrected

Un-corrected vs corrected time series.

Task 3.4: Validation of the OMI SO 2 over the city of Thessaloniki

Sciamachy : all data SO 2 TRL Thessaloniki

Sciamachy : no backward pixels, SZA cut-off at 75° SO 2 TRL Thessaloniki

OMI : all data SO 2 TRL Thessaloniki

OMI : all data, averaged within 50km SO 2 TRL Thessaloniki

OMI : data averaged within 50km, CTP & SZA cutoff SO 2 TRL Thessaloniki

Using the instantaneous data from the Thessaloniki Brewer SO 2 PBL comparison

Using the instantaneous data from the Thessaloniki Brewer SO 2 PBL comparison with a 2 D.U. cut-off

Task 3.3: Validation of Sciamachy SO 2 over Europe and China with Brewer spectrophotometers

Three in China & Two in Korea & One in Hong-Kong

Task 3.3: Validation of Sciamachy SO 2 over Europe and China with Brewer spectrophotometers

Arosa 46.77° North

Hohenpeissenberg 47.80°North

Sodankyla 67.37° North

Mt Waliguan 36.17° North China, at 4km altitude

Mt Waliguan 36.17° North China, at 4km altitude

Pohang 36.03° North Korea

Pohang 36.03° North Korea

Cape d’Aguilar 22.24° North Hong Kong

Cape d’Aguilar 22.24° North Hong Kong

Results from all stations

Sciamachy : all data SO 2 TRL Europe & China

Sciamachy : no backward pixels, SZA cut-off at 75° SO 2 TRL Europe & China

OMI : data averaged within 50km, CTP & SZA cutoff SO 2 TRL Europe & China

The choice is upon us  Ground-based data: scarce, quality low.  Sciamachy/Envisat data: Using carefully selected cut-off values comparisons improve.  OMI/Aura: No difference observed between using the closest observation and the mean of the observations within 50km of the overpass.

The future steps

Task 3.1: Validation of satellite-retrieved aerosol properties over a wide range of geolocations over Europe and China using ground-based results from the AERONET network. Task 3.2: Validation of satellite-retrieved aerosol properties over the city of Thessaloniki using a dedicated ground-based Brewer spectrophotometer. Task 3.3: Validation of satellite-retrieved SO 2 pollution fields over a wide range of geolocations over Europe and China where ground- based Brewer spectrophotometers exist. Task 3.4: Validation of the satellite-retrieved SO 2 pollution fields over the city of Thessaloniki using the coincident to the satellite overpass ground-based Brewer spectrophotometers measurements. Task 3.5: Validation of satellite-retrieved tropospheric O 3 slant columns over selected Chinese and European stations that include ozone sondes. Work package 3: Validation of aerosol properties, SO 2 and O 3 amounts

Task 3.5: Validation of satellite-retrieved tropospheric O 3 slant columns over selected Chinese and European stations that include ozone sondes. Next three months:  Algorithm development in preparation for Task 3.5  Quality control and selection of WOUDC and SHADOZ data  Compile tropospheric ozone time series from WOUDC and SHADOZ data.  Validate against the satellite data.