Eliezer Ganor

The Effects of Desert Particles Coated with Sulfate on Rain Formation in the Eastern Mediterranean

Abstract Measurements of aerosol composition in the eastern Mediterranean reveal that sulfate is found in most aerosol particles. Some of the large particles contain mixtures of chemicals such as sulfate and sea salt. The most striking observation is the discovery that mineral dust particles often get coated with sulfate and other soluble materials. The amount of soluble material on these particles is found to be related to their surface area, suggesting that the deposition process could be surface dependent. The mechanism by which sulfate is found on some of the mineral dust particles is believed to originate from evaporating cloud drops, which were originally nucleated on sulfate cloud condensation nuclei (CCN) and subsequently collected dry interstitial mineral dust particles. The presence of soluble material on mineral dust particles, converts the latter into effective giant CCN. This is further corroborated by the fact that the few large drops near the bases of convective clouds near the coast of Isr...

Transport of Saharan dust across the eastern Mediterranean

Earlier studies estimated the production of natural dust from the Saharan desert to be between 200 and 260 million ton per year. These figures were based solely on the westward transport of Saharan dust. In this study estimates on the dust transport to the eastern Mediterranean are provided. The data were obtained from several studies concerned with dust storms in Israel including: ground and airborne particle mass concentration, vertical profiles, dust storm trajectories, particle deposition and the climatology of dust storms in the eastern Mediterranean. A simple two dimensional transport model applied to the above data yields a production rate of 70 million tons of Saharan dust y−1 which are transported eastward. About one third of this amount reaches the east Mediterranean coast located at a distance of 2000 km from the Saharan source.

Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index

[1] We proposed to identify the sources of desert dust aerosols with local maxima of the TOMS aerosol index distribution averaged for the long period. Being simpler than the approach based on a dusty days occurrence, our method gives the same results. It was first shown that in spring-summer, the flux of dust from the sources located at latitude � 16� N and longitude � 16� E and around latitude � 19� N and longitude � 6� W exceed the sinks due to settling and transport. As a result the atmosphere over North Africa is almost permanently loaded with a significant amount of mineral desert dust in spring and in summer. It is also shown that the Chad basin source located around latitude 16� N and longitude 16� E is relatively more stable with a maximum activity around April. The region around latitude 19� N and longitude 6� Wappears as a more variable source with maximum in July. Low pressure systems, called Sharav cyclones, mobilize the already suspended mineral dust and transport it eastward and northward along the Mediterranean basin. A new method for description of dust plumes propagation was applied to the study of dust events in the Mediterranean Sea and enabled us to follow their dynamics. Identifiable dust plumes appear first in the western sector of the sea and then move eastward with a speed of about 7 to 8 degrees per day. In spring, this motion continues at least up to the eastern coast of the Mediterranean. In summer the dustplume is prevented from penetrating further east of about 15� E. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 4801 Oceanography: Biological and Chemical: Aerosols (0305); KEYWORDS: Aerosols, desert dust, dust storms, dust sources, Mediterranean Citation: Israelevich, P. L., Z. Levin, J. H. Joseph, and E. Ganor, Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index, J. Geophys. Res., 107(D21), 4572, doi:10.1029/2001JD002011, 2002.

The chemical composition of aerosols settling in Israel following dust storms

Abstract The chemical composition of settling particles from 23 heavy dust storms in Israel has been determined. These storms occurred over a 20-year period in Jerusalem and Ramat Hasharon, north of Tel Aviv. Meteorological conditions during the storms were examined and the storms classified according to their trajectories into two types: (a) North African; and (b) Arabian Desert. The North African type is by far the most common. The composition of the dust storms is monotonic. Additional interpretation of the chemical analyses using Enrichment Factors reveals the following points. (1) The settling particles are relatively enriched in Ca probably from the local terrain and in Cl derived from the Mediterranean Sea. They are also enriched in S for unexplained reasons. Other elements enriched include Pb and Br and these are presumably due to contamination from the use of leaded petrol. (2) Comparison of the two types of dust storms shows that the Arabian Desert type contains less Cl and U. The composition of an Israel Background Reference Standard is suggested for use in future ecological studies of settling particles in Israel.

Induced sputum assessment in New York City firefighters exposed to World Trade Center dust.

New York City Firefighters (FDNY-FFs) were exposed to particulate matter and combustion/pyrolysis products during and after the World Trade Center (WTC) collapse. Ten months after the collapse, induced sputum (IS) samples were obtained from 39 highly exposed FDNY-FFs (caught in the dust cloud during the collapse on 11 September 2001) and compared to controls to determine whether a unique pattern of inflammation and particulate matter deposition, compatible with WTC dust, was present. Control subjects were 12 Tel-Aviv, Israel, firefighters (TA-FFs) and 8 Israeli healthcare workers who were not exposed to WTC dust. All controls volunteered for this study, had never smoked, and did not have respiratory illness. IS was processed by conventional methods. Retrieved cells were differentially counted, and metalloproteinase-9 (MMP-9), particle size distribution (PSD), and mineral composition were measured. Differential cell counts of FDNY-FF IS differed from those of health care worker controls (p < 0.05) but not from those of TA-FFs. Percentages of neutrophils and eosinophils increased with greater intensity of WTC exposure (< 10 workdays or ≥ 10 workdays; neutrophils p = 0.046; eosinophils p = 0.038). MMP-9 levels positively correlated to neutrophil counts (p = 0.002; r = 0.449). Particles were larger and more irregularly shaped in FDNY-FFs (1–50 μm; zinc, mercury, gold, tin, silver) than in TA-FFs (1–10 μm; silica, clays). PSD was similar to that of WTC dust samples. In conclusion, IS from highly exposed FDNY-FFs demonstrated inflammation, PSD, and particle composition that was different from nonexposed controls and consistent with WTC dust exposure.

The composition of clay minerals transported to Israel as indicators of Saharan dust emission

Abstract Ambient particles, following dust storms originating in the Saharan region as identified by meteorological analysis of synoptic maps, satellite pictures and back-trajectory calculations, transported over Israel, were collected and analysed. In studies of 28 heavy dust storms originating in the Saharan region, during a 22 year period (1967–1988), clay mineral analysis provided information about the characteristics of dust particles transported over Israel. Relatively high concentrations of montmorillonite and mixed-layer minerals were found in the particles when the storms originated on the western deserts of the Tibesti mountains. Following storms that originated in Saudi Arabia, Jordan and the Dead Sea deserts, the dust particles contained a high percentage of palygorskite. Following storms that originated in the Chad, Lybian plateau deserts and the Great Sand Sea of Ahaggar Massif, predominantly high concentrations of illite was found in the ambient particles in Israel. These data indicate that ambient particles in Israel following dust storms originating in the Saharan region may be characterized by their mineral content.

The contribution of sulfate and desert aerosols to the acidification of clouds and rain in Israel

Abstract Measurements of the sulfate content in individual particles were carried out on top of a mountain in Northern Israel in order to determine the role played by acidic sulfate particles in changing the pH of cloud drops. The investigation was carried out during the passage of convective clouds over the station. Since these clouds developed in cold fronts originating from different air masses it was possible to determine the role of sulfate as well as desert particles in affecting the chemistry of cloud and raindrops. It was observed that the cloud droplets were frequently very acidic with the pH as low as 2.5. As the cloud droplets grew by condensation they became less acidic due to dilution. The presence of desert particles did not affect the pH of the cloud droplets since they remained as interstitial particles. However, once rain started the pH of the raindrops was found to be as high as 8.2. On these occasions the drops contained large amounts of dust indicating that the process of scavenging either by te cloud drops or by the falling melting graupels is very efficient. Sulfate concentrations in air containing large amounts of dust were found to be much higher than on days lacking dust aerosols. The source of these sulfate particles has not yet been identified.

Aerosol composition of urban and desert origin in the eastern Mediterranean

Aerosol samples were collected in Tel-Aviv, Israel, during two different atmospheric situations, clear days and dust storms, and were analyzed for shape, size distribution, elemental composition, and presence of sulfate in individual particles. Results of two cases are presented in this paper. In both cases about 80% of the 0.2 to 2.0 µm particles contained sulfate. On the clear day over 50% of the total were pure sulfates while 27% were mixed sulfates; on the dusty day 63% were mixed sulfates — desert particles coated with sulfate — and only 20% were pure sulfates. The sulfate content of the desert particles was fairly high, on the order of 0.1 g sulfate g−1 of desert particles. A possible explanation of this phenomenon may be heterogeneous nucleation of SO2 on the surfaces of insoluble desert particles during their passage over the Mediterranean.

A jet stream associated heavy dust storm in the Western Mediterranean

Examination of the dynamical structure of a heavy dust storm event over the western Mediterranean revealed an almost exact coincidence of the western boundary of the dust plume with a cold front and a significant jet stream. A confrontation was found between the dry desert air mass associated with a notable downward flowing jet stream and the moister Mediterranean air mass. Vertical cross sections across and along the dust plume indicated that the high mountain Ahaggar region over the Sahara was probably the source of dust, which was transported northward more than 2400 km and washed out by heavy rainfall.

Acid rain on Mt Carmel, Israel

Wetfall and bulkfall were collected on Mt Carmel, Israel, for three hydrological years, 1989–1992, using an acid precipitation sampler equipped with a moving cover. The analysis of 40 rain events indicated that in more than 65% of the events the pH was acid (<5–6) and in nearly 40% of the events strongly acid. Only in 12% of the events was the pH distinctly alkaline. Bulkfall collected on the same site had a higher pH, due to much higher Ca2+ and K+ concentrations, suggesting the effects of local aerosols emanating from calcareous soils. The relatively high Na+ and Cl− levels and their Na+/Cl− ratio of 0.866 indicated the marine origin of the major portion of dissolved salts. Alkaline wetfall, strongly enriched in K+, Cl− and Na+, was associated with duststorms. X-ray and chemical analysis of the dryfall (dust) showed the presence of quartz, carbonates, clay minerals, feldspar, halite and gypsum. SO42−, responsible for the acidity of the wetfall, appears to be imported from Central or Eastern Europe, via the Mediterranean Sea, as suggested by back-trajectories of 26 rain events.