AMFIC second progress meeting

MariLiza Koukouli & Dimitris Balis Laboratory of Atmospheric PhysicsAristotle 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 SO2 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 SO2 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 O3 slant columns over selected Chinese and European stations that include ozone sondes.

Work package 3: Validation of aerosol properties, SO2 and O3 amounts

Work package 3: Validation of aerosol properties, SO2 and O3 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 SO2 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 SO2 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 O3 slant columns over selected Chinese and European stations that include ozone sondes.

The SO2 issue over Europe

The SO2 issue over China

Brewer SO2 data

From the original 84 stations that provide total DAILY SO2 columns in www.woudc.org, 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 SO2 Brewer measurements

Brewer SO2 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 SO2 measurementsBrewers measure UV at five wavelengths, four longer wavelengths are

used to derive ozone, the fifth (shortest) wavelength is used only for SO2. There are several sources of errors in Brewer SO2 measurements:

  Stray light. Since SO2 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 SO2 at high zenith angles and under high total ozone conditions. SO2 can be negative due to this problem.

The ExtraTerrestrialConstant errors. Unlike ozone, it is difficult to determine ETC for SO2 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 SO2 measurements Wavelength/absorption coefficient. The Brewer wavelength

and  the instrument sensitivity are not exactly the same for all instruments. Errors in effective SO2 absorption coefficient introduces a bias, while wavelength shifts affect also the ETC causing more complicated errors.

 So, errors in SO2 measurements are rather large and

complicated. Present SO2 algorithms might not be suitable for estimation of "background" SO2 levels.

Vitali Fioletov, private communication

Sciamachy SO2 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 SO2 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 SO2 data

Overpass files within 50 km of centre downloaded from http://avdc.gsfc.nasa.gov/

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 SO2 data

Four SO2 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 SO2 last May

1. Calibration of Thessaloniki Brewer SO2 dataset2. 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 < 0.20

4. 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 SO2 over

the city of Thessaloniki

Task 3.4: Validation of the Sciamachy SO2 over the city of Thessaloniki, plume @ 1km

Task 3.4: Validation of the Sciamachy SO2 over the city of Thessaloniki, plume @ 6km

Task 3.4: Validation of the Sciamachy SO2 over the city of Thessaloniki

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Task 3.4: Discussion of the Thessaloniki Brewer total SO2 : corrected

Un-corrected vs corrected time series.

Task 3.4: Validation of the OMI SO2 over the city of Thessaloniki

Task 3.4: Validation of the OMI SO2 over the city of Thessaloniki

Sciamachy : all data SO2 TRLThessaloniki

Sciamachy : no backward pixels, SZA cut-off at 75° SO2 TRLThessaloniki

OMI : all data SO2 TRLThessaloniki

OMI : all data, averaged within 50km SO2 TRLThessaloniki

OMI : data averaged within 50km, CTP & SZA cutoff SO2 TRLThessaloniki

Using the instantaneous data from the Thessaloniki Brewer

SO2 PBL comparison

Using the instantaneous data from the Thessaloniki Brewer

SO2 PBL comparison with a 2 D.U. cut-off

Task 3.3: Validation of Sciamachy SO2 over Europe and

China with Brewer spectrophotometers

Task 3.3: Validation of Sciamachy SO2 over Europe and China with Brewer spectrophotometers

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

Task 3.3: Validation of Sciamachy SO2 over Europe and China with Brewer spectrophotometers

Arosa 46.77° North

Arosa 46.77° North

Hohenpeissenberg 47.80°North

Hohenpeissenberg 47.80°North

Sodankyla 67.37° 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° NorthHong Kong

Cape d’Aguilar 22.24° NorthHong Kong

Results from all stations

Sciamachy : all data SO2 TRLEurope & China

Sciamachy : no backward pixels, SZA cut-off at 75° SO2 TRLEurope & China

OMI : data averaged within 50km, CTP & SZA cutoff SO2 TRLEurope & 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 SO2 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 SO2 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 O3 slant columns over selected Chinese and European stations that include ozone sondes.

Work package 3: Validation of aerosol properties, SO2 and O3 amounts

Task 3.5: Validation of satellite-retrieved tropospheric O3 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.