Interrelationships between aerosol characteristics and light scattering during late winter in an Eastern Mediterranean arid environment

An intensive field campaign involving measurement of various aerosol physic al, chemical, and radiative properties was conducted at Sde Boker (also wri tten as Sede Boqer) in the Negev Desert of Israel, from is February to 15 M arch 1997, Nephelometer measurements gave average background scattering coe fficient values of about 25 Mm(-1) at 550 nm wavelength, but strong dust ev ents caused the value of this parameter to rise up to about 800 Mm(-1). Bac kscattering fractions did not depend on aerosol loading and generally fell in the range of 0.1 to 0,25, comparable to values reported for marine and A rctic environments. Chemical analysis of the aerosol revealed that in the c oarse size range (2-10 mu m equivalent aerodynamic diameter (EAD)), calcium (Ca) was by far the most abundant element followed by silicon (Si), both o f which are indicators for mineral dust. In the fine size fraction (<2 mu m EAD), sulfur (S) generally was the dominant element, except during high du st episodes when Ca and Si were again the most abundant. Furthermore, fine black carbon (BC) correlates with S, suggesting that they may have originat ed from the same sources or source regions, An indication of the shortterm effect of aerosol loading on radiative forcing was provided by measurements of global and diffuse solar radiation, which showed that during high-turbi dity periods (strong dust events), almost all of the solar radiation reachi ng the area is scattered or absorbed.