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

Spectral measurements of the aerosol particle scattering coefficient sigma (s) and the aerosol optical depth tau (a) were conducted at Ouranoupolis (G reece, 40 degrees 23'N, 23 degrees 57'E) and at Sde Boker (Israel, 30 degre es 51'N, 34 degrees 47'E) between June and September 1998. Measurements wer e 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 t he eastern Mediterranean basin is moderately to highly polluted during summ er. Daily average sigma (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 ae rosol optical depth tau (a) was 0.03-0.52 at 500 nm. Enhanced aerosol extin ction was related to transport of polluted air masses from western and east ern Europe. High-altitude transport of mineral dust from northern Africa wa s observed at both sites, particularly in Israel.