Aerosol optical depth at ALOMAR Observatory (Andøya, Norway) in summer 2002 and 2003

Two intensive campaigns were carried out by the Atmospheric Optics Group of Valladolid University (GOA-UVA) during summer 2002 and 2003 at ALOMAR station (Andøya island, Norway, 69◦16 N, 16◦00 E), allowing an aerosol characterization and classification in this coastal Arctic region during the summer. Aerosol measurements were performed with a Cimel sun photometer at the four nominal aerosol wavelengths 440 nm, 670 nm, 870 nm and 1020 nm. Spectral measurements in the range 300–1100 nm with a field spectroradiometer Licor-1800 were also performed during 2003, allowing a comparison with Cimel data. The agreement between both instruments is inside the current error for field aerosol optical depth retrieval, namely, 0.02. Although aerosol optical depth (AOD) at the nominal wavelength of 440 nm has an average value below 0.12, values range from 0.04 to 0.36. DerivedA ngstr¨om alpha coefficient gives an average value about 1.6 (STD 0.2), meaning predominance of fine particles. These values do not fit the typical maritime aerosol characteristics. Continental and long-range transport air masses seem to influence this area, giving rise to mixed aerosols. Back trajectory analysis shows the predominance of Atlantic air masses with low AOD, while continental air masses show in general larger aerosol loading.