Dust and pollution aerosols over the Negev desert, Israel: Properties, transport, and radiative effect

The complex spatial, temporal, and optical characteristics of atmospheric aerosols cause large uncertainties in the estimation of aerosol effects on climate. Analysis of long-term measurements from key regions can provide a better understanding of the role of atmospheric aerosols in the climate system. In the current study, observations of aerosol optical properties and mass concentrations were carried out during 1995-2003 in the Israeli Negev desert. The measurement site is relatively remote from local pollution sources; however, it lies at the crossroad between dust from the Sahara and the Arabian peninsula and pollution from Europe. The instruments employed were a Sun/sky photometer, a stacked filter unit sampler, and an integrating nephelometer. We analyzed the data for seasonal variability, general vertical aerosol structure, and radiative climate effect by dust and anthropogenic aerosol. The intra-annual variability of aerosol optical properties was found to be closely related to seasonally varying synoptic conditions. Two seasonal peaks of aerosol optical thickness were noted: The first maximum related to dust particle activity and the second to anthropogenic aerosol. Similar maximums were noted in aerosol light scattering at the surface; however, their relative importance is reversed and is related to differences in the vertical distribution of dust and anthropogenic aerosols. The calculated aerosol radiative effect shows cooling both at the top of the atmosphere and at the surface during the whole year. The radiative effect of the airborne dust is the dominating forcing component during most of the time in the study area.