Aerosol optical properties and large-scale transport of air masses: Observations at a coastal and a semiarid site in the eastern Mediterranean during summer 1998

Spectral measurements of the aerosol particle scattering coefficient δ_s and the aerosol optical depth τ_a were conducted at Ouranoupolis (Greece, 40°23′N, 23°57′E) and at Sde Boker (Israel, 30°51′N, 34°47′E) between June and September 1998. Measurements were related to 5-day three-dimensional back trajectories at 950, 850, and 550 hPa to assess the influence of long-range transport from particular source regions to the aerosol load at the two sites. Our measurements show that the eastern Mediterranean basin is moderately to highly polluted during summer. Daily average δ_s values at 550 nm were typically in the range of 30-200 Mm^-1 at both sites. The range obtained for the summer regional aerosol optical depth τ_a was 0.03-0.52 at 500 nm. Enhanced aerosol extinction was related to transport of polluted air masses from western and eastern Europe. High-altitude transport of mineral dust from northern Africa was observed at both sites, particularly in Israel.