Atmospheric sulfur flux rates to and from Israel

Both field measurements and model simulation studies have shown that Israel is the recipient of long range transported air pollutants that originated over various parts of Europe. The present paper presents results of aircraft measurements aimed at quantitizing the sulfur flux arriving at Israel's western coast from Europe and the Israeli pollution contribution to the air masses leaving its eastern borders towards Jordan. During the research flights, measurements of sulfur dioxide and sulfate particulates and meteorological data were recorded. Two different legs were performed for each research flight: one over the Mediterranean Sea, west of the coast and the second along the Jordan Valley. All flights were carried out at a height of approximately 300 m above ground level. A total of 14 research flights were performed covering the summer and autumn seasons. The results indicate that the influx of sulfur arriving at the Israeli coast from Europe varied in the range of 1-30 mg S/h, depending on the measuring season. The particulate sulfate level in the incoming LRT air masses was at least 50% of the total sulfur content. The contribution of the local pollutant sources to the outgoing easterly fluxes also varies strongly according to season. During the early and late summer, the Israeli sources contributed an average of 25 mg S/h to the total pollution flux as compared to only approximately 9 mg S/h during the autumn period. Synoptic analysis indicates that conditions during the summer in Israel favor the accumulation of pollution species above the Mediterranean basin from upwind European sources. This season features a shallow mixed layer and weak zonal flow leads to poor ventilation rates, inhibiting an efficient dispersion of these pollutants while being transported eastward. Under these conditions, in flux, local contribution and the total out-flux of these pollutants are elevated as opposed to during other seasons. During the fall, the eastern Mediterranean region is usually subjected to weak easterly winds, interrupted at times by strong westerly wind flows inducing higher ventilation rates. These meteorological conditions and the lack of major emitting sources eastwards of Israel result in lower sulfur budgets to and from Israel for this season. An estimate of the yearly flux showed that approximately 0.06 tg S arrived at the Israeli coast from the west. This is approximately 15% of the estimated pollution leaving Europe towards the eastern edge of the Mediterranean basin. The local contribution to the out-flux towards Jordan was calculated to be 0.13 tg S per year, almost all of the sulfur air pollutants emitted in Israel.