Airborne particle accumulation and composition at different locations in the northern Negev desert

Atmospheric desert dust was collected over 36 months in ground-level collec tors at four stations in the northern Negev desert, Israel. Three stations (Shivta, Sede Boqer and Avdat) are located in the desert itself whereas the fourth station (Sayeret Shaked) is situated at the desert fringe, in the t ransition zone between the true desert and the more humid area to the north . The dynamics of the dust in the three desert stations is similar and diff ers from that at the desert fringe station. In the desert, dust accumulatio n is highest in summer and lowest in winter, whereas the situation is rever se at the desert fringe. Also, the amount of accumulation is much higher in the desert itself. No important differences are observed with respect to t he average grain size of the dust, but the temporal evolution in grain size variability at the desert fringe is different from that in the desert. Mineralogical analysis by means of X-ray diffraction shows that quartz and calcite, and to a lesser extent also dolomite, are the major constituents o f the Negev dust. There is a good agreement between the quartz and calcite content of the dust samples and that of the outcropping rocks located sligh tly upwind of the four stations, suggesting that at least an important part of the dust collected is of rather local origin. However, the regular reco rds of dust haze events in the northern Negev show that part of the dust th at accumulates in this region is not of local origin, but originates from d istant sources. This dust may later mix with the local dust.