Climatological aspects of aerosol optical properties in Northern Greece

Abstract

Abstract.Measurements of aerosol optical properties (aerosol optical depth, scattering and backscattering coefficients) have been conducted at two groundbased sites in Northern Greece, Ouranoupolis (40 • 23 N, 23 • 57 E, 170 m a.s.l.) and Thessaloniki (40 • 38 N, 22 • 57 E, 80 m a.s.l.), between 1999 and 2002. The frequency distributions of the observed parameters have revealed the presence of individual modes of high and low values, indicating the influence from different sources. At both sites, the mean aerosol optical depth at 500 nm was 0.23. Values increase considerably during summer when they remain persistently between 0.3 and 0.5, going up to 0.7-0.8 during specific cases. The mean value of 65±40 Mm −1 of the particle scattering coefficient at 550 nm reflects the impact of continental pollution in the regional boundary layer. Trajectory analysis has shown that higher values of aerosol optical depth and the scattering coefficient are found in the east sector (former Soviet Union countries, eastern Balkan countries), whereas cleaner conditions are found for the NW direction. The influence of Sahara dust events is clearly reflected in the Angström exponents. About 45-60% of the observed diurnal variation of the optical properties was attributed to the growth of aerosols with humidity, while the rest of the variability is in phase with the evolution of the sea-breeze cell. The contribution of local pollution is estimated to contribute 35±10% to the average aerosol optical depth at the Thessaloniki site during summer. Finally, the aerosol scale height (aerosol optical depth divided by scattering coefficient) was found to be related to the height of the boundary layer with values between 0.5-1 km during winter and up to 2.5-3 km during summer.

Physical and optical properties of aerosols over an urban location in Spain: seasonal and diurnal variability

“…Saha et al (2008) reported similar seasonal variations of aerosol scattering and absorption coefficients at an urban costal site, Toulon, France, where the largest values of σ sp and σ ap were observed in winter and the lowest values in summer. In addition, the mean value of σ sp (61±31 Mm −1 at 550 nm) observed at Granada is similar to the σ sp (525 nm)=60 Mm −1 obtained at this urban costal site during (Saha et al, 2008 and is almost comparable to those obtained in northern Greece (65±31 Mm −1 ) and Sede Boker, Israel (60±31 Mm −1 ) by Gerasopoulos et al (2003) and Derimian et al (2006), respectively. However, our σ sp average value is relatively larger than the average values measured by Pereira et al (2008), at Evora, Portugal (46 Mm −1 ), and by Vrekoussis et al (2005), in remote areas of Greece and Turkey (50 and 45 Mm −1 ).…”

Variability of aerosol optical properties in the Western Mediterranean Basin

“…As shown in this work, the in-situ measurements are helpful in order to describe the effects of mesoscale weather systems such as the breeze circulation on aerosol optical properties. A number of studies have been published on in-situ aerosol optical measurements in the Eastern Mediterranean (Vrekoussis et al, 2005;Ichoku et al, 1999;Formenti et al, 2001;Sciare et al, 2005;Kouvarakis et al, 2002;Andreae et al, 2002;Gerasopoulos et al, 2003;Sabbah et al, 2001;Israelevich et al, 2002), Central Mediterranean and South Italy (Pace et al, 2006;Esposito et al, 2004), South Iberian Peninsula (Pereira et al, 2011;Lyamani et al, 2008). However, little has been published on aerosol optical properties in the Western Mediterranean Basin (Mallet et al, 2003;Saha et al, 2008).…”

Nine years of UV aerosol optical depth measurements at Thessaloniki, Greece

“…The average value of theÅngström coefficient, α, for the entire dataset was estimated to 1.63±0.53. Gerasopoulos et al (2003) found anÅngström coefficient of 1.57±0.28 using one year (2001) of data from a Multifilter Radiometer (MFR) at the same location. The MFR measures the global and diffuse irradiance at selected wavelengths in the visible part of the spectrum.…”

“…In the last decade, a substantial number of experimental studies on aerosols has been focused on the eastern Mediterranean area (Luria et al, 1996;Pinker et al, 1997;Mihalopoulos et al, 1997;Papayannis et al, 1998Papayannis et al, , 2005Formenti et al, 2001Formenti et al, , 2002Lelieveld et al, 2002;Gerasopoulos et al, 2003;Balis et al, , 2004Amiridis et al, 2005). Various model studies predicted maximum net direct radiative forcing by sulfate aerosols for this region (Charlson et al, 1991;Kiehl and Published by Copernicus GmbH on behalf of the European Geosciences Union.…”