Natural versus anthropogenic aerosols in the eastern Mediterranean basin derived from multiyear TOMS and MODIS satellite data

Abstract

[1] In the present study we investigate the spatial and temporal variation of aerosol optical thickness (AOT) in the eastern Mediterranean basin, and more specifically in the area extending from 28.5°N to 42.5°N and from 18.5°E to 35.5°E, which includes large urban areas and megacities such as Cairo, Istanbul, Athens, Izmir, Ankara, and Thessaloniki. For this purpose we use long-term AOT data from the Total Ozone Mapping Spectrometer (TOMS) version2 converted to 500 nm (AOT 500 ) for the period 1980-2001 and Collection 005 AOT data at l = 550 nm (AOT 550 ) from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites for the periods 2000-2005 and 2002-2005, respectively. The spatial and temporal variation of AOT shows a good agreement between TOMS and MODIS, in terms of geographical patterns, which maximizes the usefulness of TOMS AOT product given its long temporal coverage (climatological). According to MODIS-Terra, the annual mean AOT 550 over the studied region equals 0.22 ± 0.05 (monthly values ranging from 0.14 to 0.32) and shows strong spatial inhomogeneities. The smallest values (down to 0.1) occur over the western, and especially in the northwestern, part of Greece, over the northern part of Anatolian peninsula and also over the sea of east Mediterranean. The largest AOT values (up to about 1.0) occur over northern Africa, Middle East, and the adjacent coasts, and over the Anatolian plateau. These high aerosol loadings are of natural origin, mainly desert dust. However, very large values (up to 0.8) are also found over large urban areas surrounding megacities, associated with anthropogenic, apart from natural desert, aerosols. By using TOMS AOT data as proxy for the dust source, and the difference of MODIS-TOMS AOT as an indicator of the anthropogenic aerosol component, the relative contribution of natural versus anthropogenic sources of aerosols has been derived for the eastern Mediterranean area. Limitations of this approach are discussed and the associated uncertainties are also evaluated and discussed.

Synoptic conditions favouring the occurrence of aerosol episodes over the broader Mediterranean basin

“…This transport is induced by the prevailing south-southwesterly winds caused by depressions moving eastwards across the North African coast. In this way, it is the central and the eastern parts of the Mediterranean basin which are mainly affected (Barnaba and Gobbi, 2004;Papadimas et al, 2008;Hatzianastassiou et al, 2009). During summer, a similar transport of Saharan dust takes place in the western Mediterranean basin (Barnaba and Gobbi, 2004;Papadimas et al, 2008) because of thermal lows located either over northwestern Africa or over the Iberian Peninsula.…”

“…Perrone et al, 2005;Fotiadi et al, 2006;Koulouri et al, 2008;Basart et al, 2009). Nevertheless, during the last decade, the rapid progress in space-based monitoring of aerosol properties has enabled scientists to perform similar studies using satellite-based products providing a complete spatial coverage (Barnaba and Gobbi, 2004;Papadimas et al, 2008;Hatzianastassiou et al, 2009). …”

Trend analysis of 41 years of sunshine duration data for Turkey

“…We should here note that the long-term reduction of SD data can be attributed to increasing aerosols and pollution, as this will result in a decrease of sunshine duration readings due to the reduction in the records during the times when the solar irradiation values are close to the threshold values of the recording instruments. Results of the study by Hatzianastassiou et al [6] on aerosol optical thickness (AOT) in the eastern Mediterranean basin shows evidence for this case and results of that study will be compared to present findings in Section 3.2.…”

Evaluation and Comparison of Long-Term MODIS C5.1 and C6 Products against AERONET Observations over China

“…By changing the global energy budget and perturbing the hydrological cycle, the global climate could be influenced by aerosols [5,6]. The fine particles of aerosol particles, PM 2.5 and PM 10 (particles with aerodynamic diameters less than 2.5 and 10 µm, respectively), penetrate into lungs and seriously affect human health if the concentrations are too high [7][8][9]. different aerosol products.…”