Optical properties of aerosol over a South European urban environment

Aerosol optical depths AODs and single scattering albedos SSAs were derived from in situ aircraft measurements of scattering and absorption coefficients at 550 nm. These values were compared to the AODs and SSAs derived from the sun photometer CIMEL data of the Aerosol Robotic Network AERONET site, in Thessaloniki, Greece, between 18 and 21 July 2006. The aircraft-obtained AODs were lower than the corresponding columnar values. However, aircraft SSAs were found to be in good agreement with the columnar values retrieved from the CIMEL. Aircraft aerosol size distributions measured by means of an optical particle counter OPC were also in good agreement with the respective distributions derived from the AERONET site. Filter samples were collected on board the aircraft at different altitudes, to provide detailed information on the chemical composition of tropospheric aerosol. The concentrations of identified chemical species were used to calculate particle refractive indices RIs for comparison with the AERONET calculated values.