Seasonal variability of optical properties of aerosols in the Eastern Mediterranean

Date

2005-12-01

Author

Vrekoussis, M
Liakakou, E
Koçak, Mustafa
Kubilay, N
Oikonomou, K
Sciare, J
Mihalopoulos, N

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The aerosol optical properties (scattering and absorption coefficients) were investigated at two remote locations in the Eastern Mediterranean in conjunction with aerosol ion composition measurements: Finokalia in the Crete Island in Greece (March 2001-June 2002) and Erdemli in Turkey (July 1999-June 2000). Ambient light-scattering coefficient (sigma(sp-532 nm)) at Finokalia had a mean value of 50 +/- 23 Mm(-1) while at Erdemli this value was 90 +/- 160 Mm(-1), due to a severe dust event that occurred from 17 to 19 April 2000. Scattering coefficients up to 5000 Mm(-1) were encountered during the transition periods (spring and autumn) and were associated with dust storm events. During these events significant correlations were observed between dust and a, and mass scattering efficiencies of 0.21 and 0.96m(2) g(-1) were calculated for dust for Finokalia and Erdemli, respectively. Significant correlations were also observed at both locations between non-sea-salt nss-SO42-); and mass scattering efficiencies of 5.9 +/- 1.8 and 5.7 +/- 1.4 m(2)g(-1) were calculated for the nss-SO42- at Finokalia and Erdemli, respectively. At Finokalia absorption measurements were also performed at the same time and the mean absorption coefficient (sigma(ap-565nm)) was found to be 5.6 +/- 3.6 Mm(-1). Maxima of absorption coefficient were associated with two distinct meteorological situations indicative of pollution transported from northern Europe and Saharan dust events. Saharan dust can therefore significantly contribute to both scattering and absorption of solar radiation, the latter due to its hematite content. Based on scattering and absorption measurements, an annual mean single- scattering albedo (omega) adjusted at 550 nm of 0. 89 +/- 0.04 was calculated for Finokalia. Finally, radiative forcing efficiency (RFE) over the sea at 550 mn induced by aerosols has been calculated for Finokalia. RFE follows a clear seasonal variation, with the lowest mean values during summer (-73W(m-2)) and the highest during winter (-30Wm(2)). Using aerosol optical thickness measurements in the area, we obtain radiative forcing estimates at the top of the atmosphere (TOA) ranging from - 12.6 to -2.3 W m(2) for summer and winter, respectively. These values are up to five times higher than that induced by the greenhouse gases (2.4 Wm(-2)) but opposite in sign.

Subject Keywords

Optical properties of aerosols, Seasonal variation, Chemical composition, Radiative forcing, Eastern Mediterranean

URI

https://hdl.handle.net/11511/30463

Journal

ATMOSPHERIC ENVIRONMENT

DOI

https://doi.org/10.1016/j.atmosenv.2005.08.011

Collections

Graduate School of Marine Sciences, Article

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Citation Formats

M. Vrekoussis et al., “Seasonal variability of optical properties of aerosols in the Eastern Mediterranean,” ATMOSPHERIC ENVIRONMENT, pp. 7083–7094, 2005, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/30463.