Size Distribution, Chemical Composition and Optical Properties of Atmospheric Dust in Israel: A Comparison of Urban and Desert Aerosols under Clear and Dusty Conditions.

Abstract : Measurements of aerosol size distributions, chemical composition and optical properties were carried out at two locations in Israel. Tel Aviv was chosen as an urban region and Mitzpe Ramon as a desert region. The measurements indicate that the size spectra between 0.15 - 12 micrometers can be approximated by a power law type distribution. The spectra in Tel Aviv show higher concentrations and greater slopes than those from the desert. Diurnal variations between day and night are observed in the size distribution of the summertime measurements in Tel Aviv. These are believed to be related to the increase in aerosol size due to absorption of water vapor during high relative humidity periods. The chemical composition in Tel Aviv was found to strongly depend on the meteorological conditions. The optical measurements also suggest strong differences between Tel Aviv and the desert. Filter samples of atmospheric particulate matter from Tel Aviv always appeared darker than those from the desert site. Measurements of imaginary refractive index in the 0.3 to 1.7 micrometer spectral region are presented. These measurements are consistently higher by a factor of 2 to 4 in Tel Aviv as compared to simultaneous samples from the desert site. Seasonal variations have also been observed and are believed to be primarily related to temperature inversions near or at the ground during the winter months and to the effect of pollution from Southern Europe which is carried eastward by synoptic scale motion.