Climatology of aerosol components

Description:

Annual mean contribution of major aerosol components to total aerosol optical thickness

Product Example
Climatology of Aerosol Components
Figure 1 : Preliminary aerosol climatology dataset based on observations of the period 4 July 1997 – 25 August 1998. The figure shows (from left to right) in the upper line: total aerosol optical thickness (AOT), total number of pixels in a grid box (ranging from 0 to 50), sulfate/nitrate optical thickness (OT); in the lower line: soot optical thickness, dust optical thickness, and sea salt optical thickness. All optical thickness values are given at 550 nm; the different range of OT values in the sub images should be noticed (total and sulfate/nitrate OT: 0-1.0; soot OT: 0 - 0.4, mineral and seasalt OT: 0 - 0.2); black boxes mean that no particles of this component were found at all in this box.

Methodology:

It is the ultimate goal of this work to produce (and in future update) a satellite based aerosol climatology for the MSG observation area. For this purpose the SYNAER method (see product daily aerosol optical thickness and type) is implemented and will soon work operationally with the sensors SCIAMACHY and AATSR onboard ENVISAT. A backup climatology production based on GOME and ATSR-2 products (both onboard ERS-2) of the year 1997/98 was produced with “small” GOME pixels of 80x40 km2 measured only for 3 days every month (SCIAMACHY will deliver pixels of 60x30 km2 for a swath of 960 km, i. e. 8 pixels in one line overlapping with AATSR).

The final aim is to deliver 4 seasonal climatology datasets with a 5 degree horizontal grid. Due to cloud coverage and method inherent limitations (surface brightness must not exceed 8%, GOME pixel cloud fraction must not exceed 35%, differentiation of aerosol types is only reliable for optical thickness at 550 nm larger than 0.1) a one year dataset (average and standard deviation optical thickness, differentiation into basic components) was obtained as first product for a 5 degree grid. Detailed handling of quality information from the retrieval process such as fit error, GOME-ATSR-2 reflectance deviation, surface brightness, spectral noise, surface elevation, cloudiness, solar elevation angle, etc. is currently under review.

As a preliminary result the figure shows the climatology dataset based on 14 months of observations (July 1997 to August 1998, 3 days per month only!). The low number of observations leads to large box-to-box variation and in some boxes even unrealistic mean optical thickness values which are determined by single episodes. This will be enhanced by using daily available data from EVISAT. However, despite of the small data base some interesting features can already be observed: Largest optical thickness values occur over / near the desert areas, whereas the Scandinavian area or oceanic zones show lowest values. Also biomass burning plumes from South Africa and Central Southern Africa are indicated over the Atlantic. The number of pixels indicates to potentially uncertain results with low number of observations (in blue). Sulfate/nitrate aerosols which are included in all modelled aerosol types as background contribution show even clearer the unpolluted oceanic and Northern areas. Soot occurs most prominently over industrialized / densely populated areas as well as in biomass burning or industrial plumes over the ocean (and due to miss-interpretation because of the simplified dust vertical structure over deserts to some extent). Dust is dominant in and around desertic areas (Sahara, Namib, Near East) and occurs with smaller amount in continental and oceanic aerosol. Sea salt seems to require further improvement (mostly over continent), but it should be noted that it gives a weaker contribution (only up to 0.2) with thus larger error bar. Erroneous inland sea salt detection is most likely due to miss-selection instead of insoluble dust particles which are modelled with too large absorption.

For questions please contact Thomas Holzer-Popp and Marion Schroedter-Homscheidt at DLR.

Major users:

Health-, Environmental- and Scientific Organisations

Relevance:

Indicator for industrial areas and biomass burning events

Publications:

Holzer-Popp, T., Schroedter-Homscheidt, M., Satellite based climatology of aerosol components, Proc., EUMETSAT user conference, Prague, 31.5. – 4.6. 2004
Holzer-Popp, T., M. Schroedter, and G., Gesell, Retrieving aerosol optical depth and type in the boundary layer over land and ocean from simultaneous GOME spectrometer and ATSR-2 radiometer measurements, 1, Method description J. Geophys. Res., 107, D24, 2002.
Holzer-Popp, T., M. Schroedter, and G., Gesell, Retrieving aerosol optical depth and type in the boundary layer over land and ocean from simultaneous GOME spectrometer and ATSR-2 radiometer measurements, 2, Case study application and validation, J. Geophys. Res., 107, D24, 2002.
Holzer-Popp, Th., Schroedter, M., Gesell, G., High Resolution Aerosol Maps Exploiting the Synergy of ATSR-2 and GOME, Earth Obs. Quarterly, 65, 19-24, 2000.
Popp, Th., Correcting atmospheric masking to retrieve the spectral albedo of land surfaces from satellite, Int. J. Rem Sens., 16, 3483-3508, 1995.