Mineralogical and chemical characterization of suspended atmospheric particles over the east Mediterranean based on synoptic-scale circulation patterns

Atmospheric Environment 43 (2009) 3963–3970

Contents lists available at ScienceDirect

Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv

Mineralogical and chemical characterization of suspended atmospheric particles over the east Mediterranean based on synoptic-scale circulation patterns Boriana Kalderon-Asael a, b, Yigal Erel a, *, Amir Sandler b, Uri Dayan c a

Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, Israel c Department of Geography, The Hebrew University of Jerusalem, Jerusalem 91905, Israel b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 December 2008 Received in revised form 30 March 2009 Accepted 31 March 2009

Suspended atmospheric particles were collected in Israel in order to identify their nature and relationships with the major synoptic-scale circulation patterns. The particles were analyzed for their major and trace element concentrations and mineralogical composition. Samples were collected during three synoptic systems associated with desert dust storms: Red Sea trough, Sharav cyclone and cold depression, and during deep and shallow modes of Persian Gulf trough, which prevails in the summer months and is not associated with dust storms. All samples mostly contain particles smaller than 2 mm. The suspended desert dust is composed primarily of illite–smectite and calcite. Some indicative secondary minerals were found for each of the dust transporting synoptic systems (e.g., palygorskite for Red Sea trough). The bulk chemistry data support the mineralogical observations and reveal additional chemical signatures of each dust transporting system. For instance, Red Sea trough samples have significantly higher Ca/Al and Ca/Mg in the carbonate and Mg/Al in Al-silicate fraction than cold depression samples. Nevertheless, Sharav cyclone samples have intermediate values in spite of the fact that the source of the dust during these conditions is similar to cold depression (i.e., North Africa). Even though differences in the chemical and the mineralogical composition of desert dust do exist, this study reveals their overall chemical and mineralogical similarities. In contrast to the synoptic systems that carry desert dust, the inorganic fraction of the Persian Gulf trough samples contains significant amount (up to 50%) of non-mineral material that has a pronounced chemical signature in terms of major element concentrations (e.g., Al, Ca, Mg, Na, S) implying their anthropogenic nature, probably from countries around the Black Sea. This striking finding is indicative for atmospheric pollution in the Eastern Mediterranean region during the summer. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: Suspended desert dust Pollution Mineralogy

1. Introduction Atmospheric mineral dust contains material produced by weathering of rocks and soils at the surface which undergo mobilization into the atmosphere by strong surface winds and convection that creates vertical turbulent mixing, and then is carried over long distances (cf. Schu¨tz, 1980). The major and most persistent sources of dust in the Northern Hemisphere are located in the ‘‘dust belt’’ that extends from 20 N to 30 N and have developed under the subtropical high-pressure subsidence. The conventional wisdom is that most of the atmospheric dust is deflated from topographical

* Corresponding author. Tel.: þ972 2 6586515; fax: þ972 2 5662581. E-mail addresses: [email protected] (B. Kalderon-Asael), yerel@ vms.huji.ac.il (Y. Erel), [email protected] (A. Sandler), [email protected] (U. Dayan). 1352-2310/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.03.057

lows (Yaalon and Ganor, 1979; Prospero et al., 2002). Nevertheless, recently it has been argued that dust originates from sand fields near these topographic lows (Mahowald, 2007; Crouvi et al., 2008), and that approximately 50% of the total atmospheric dust mass originates from disturbed soils (Tegen et al., 1996). Eolian desert dust reaches the east Mediterranean from the North African and Arabian deserts (Dayan, 1986; Ganor et al., 1991; Chester et al., 1977, 1996; Ganor and Foner, 1996, 2001; Israelevich et al., 2003). One hundred and fifty million tons out of the one billion tones of dust originating from North Africa are transported to the Mediterranean basin (Carlson and Prospero, 1972; d’Almeida, 1986; Moulin et al., 1998). In general, the grain size distributions of settled desert dust in Israel are in the range of 30–70 mm (Singer et al., 2003) and the median grain size of a single dust event decreased from w40 mm in southern Israel to w20 mm in the north (Yaalon and Ganor, 1979). On the other hand, very few

3964

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

measurements of the grain size distribution of suspended dust were carried out in Israel (Alpert and Ganor, 2001; Falkovich et al., 2001). The major synoptic systems that bring desert dust from the Arabian and Saharan deserts in the spring, fall and winter to the east Mediterranean are Red Sea trough (RS), Sharav cyclone (SC) and cold depression (CD) (Formenti et al., 2001). The geographical location of Israel between the North African and Arabian deserts and the Mediterranean climate zones makes it vulnerable also to aerosols from European sources (Dayan, 1986). In the summer, when Persian Gulf trough (PT) synoptic system dominates, it has been shown that the lower troposphere in the East Mediterranean region receives substantial amounts of atmospheric pollutants from European sources (Luria et al., 1996; Wanger et al., 2000; Lelieveld et al., 2002; Matvev et al., 2002; Dayan and Levy, 2005; Erel et al., 2007). Red Sea trough is an extension of a low surface pressure from a tropical depression toward the Red Sea, which sometimes penetrates north as far as Turkey and migrates along a mostly NorthSouth direction. Sharav cyclone is a thermal low, which is enhanced by vigorous boundary level baroclinicity caused by the steep thermal gradient existing between the heated land and the cold Mediterranean Sea (Alpert and Ziv, 1989). Cold depressions (or also called mid-latitude cyclones) are disturbances of the polar front, which extent southward. Sometimes the CD has a rather southerly track and the steep pressure gradient passes over the North African coast deflating large amounts of dust and sand (Ganor and Mamane, 1982). RS storms carry dust from eastern to south-eastern sources (i.e., Saudi Arabia), while during SC and CD the dust sources are in the south, south-west to west (i.e., North Africa). Saharaoriginated dust storms often have higher dust loads and occur in deeper atmospheric layers for longer periods of time relative with Arabian dust (Dayan et al., 1991). In the summer the Persian Gulf trough synoptic system (PT) prevails in the east Mediterranean. This system is a surface thermal barometric trough which is confined to the shallow atmospheric layers (up to about 1000 m AMSL). This system carries cool and humid air masses onshore causing a persistent elevated marine inversion. The PT is capped by a much warmer and subsiding dry air of a subtropical high-pressure system centered over North Africa and the Middle East. Persian trough is sorted into two modes (shallow and deep) according to the surface pressure gradient between Nicosia (Cyprus) and Cairo

(Egypt) and their associated thermal inversion base heights (Bitan and Sa’aroni, 1992; Koch and Dayan, 1992; Dayan et al., 2002). Evidence for the association between certain synoptic conditions and air pollution episodes over the East Mediterranean (Dayan and Levy, 2005) led us to adopt similar synoptic categorization in the current study. Meteorological analyses were combined with chemical and mineralogical characterization of suspended desert dust and aerosols during the synoptic conditions outlined above. This study focuses on the inorganic, ‘‘mineral’’ fraction (represented by the concentrations of Al, Ca, Mg, Si, etc.) of the aerosols. According to the conventional wisdom this fraction represents the natural, crustal component in atmospheric particles. We present the chemical and mineralogical composition of the desert dust of the three relevant synoptic systems and then, outline the differences between the mineral-dominated compositions of desert dust and the non-natural characteristics of the inorganic fraction of atmospheric particles during Persian Gulf trough conditions. 2. Experimental methods 2.1. Sampling Sampling was carried out using a fully automated Time-Resolution Aerosol Sampler. The sampler holds up to ten 47 mm WhatmanÒ membrane PTFE filters with pore size of 0.5 mm. Sampling was carried out in two sampling sites. Eleven dust storms and five PT events were sampled at the Hebrew University Givat Ram Campus, west Jerusalem, c. 750 m AMSL. Two dust storms (3/ 17-19/2003, 1/22-26/2006) were sampled in Shoresh, on the western slope of the Judea Hills, c. 720 m AMSL. More details about the sampling are given in the supplementary material. 2.2. Sample preparation and chemical analysis Filters were prepared and leached according to the protocol outlined in supplementary material. Following leaching of the filters the aliquots were analyzed by an ICP-MS (Perkin Elmer SCIEX, Elan DRC II) for major and trace elements (Na, Mg, Al, Ca, Ni, Cu, Zn, Pb) using Re and Rh as internal standards and calibrating the ICP-MS with Merck external multi-element standards. For most elements the detection limit of the ICP-MS was 10 ppt

1400 1200

PM10 (µg/m3)

1000 800 600 400 200

3/2/2004

3/12/2003

3/10/2003

3/8/2003

3/6/2003

3/4/2003

3/2/2003

3/12/2002

3/10/2002

3/8/2002

3/6/2002

3/4/2002

3/2/2002

3/12/2001

3/10/2001

3/8/2001

3/6/2001

3/4/2001

0

Fig. 1. Daily averaged concentrations of PM10 in mg/m3, as measured by the monitoring station of the Ministry of the Environment in Safra Square, Jerusalem, during the time period 01 April 2001 to 01 March 2004. The dust storms studied in this research are marked: Red Sea trough – blue (14 filters), Sharav cyclone – orange (34 filters), cold depression – red (28 filters), deep Persian trough – green (10 filters) and shallow Persian trough – violet (20 filters).

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

and the precision was always better than 5% as verified by running selected standards and samples several times during the run. Elemental concentrations (after subtraction of the blank filter) in both leaching fractions were used to compare between dust sources. In order to evaluate the extent of pollution of the deep and shallow modes PT samples and the dust storm samples, enrichment factors relative to Al were calculated (Rahn, 1975a; Rahn, 1975b; Buat-Menard and Chesselet, 1979; Sutherland, 2000; Erel et al., 2006). The data for the elemental concentrations in the upper continental crust were taken from Taylor and McLennan (1985). 2.3. Microscopic analysis The chemical composition and the size of aerosol particles were examined by several instruments: (1) JEOL 8600 JXA electron

3965

micro-probe (EPMA; three dust samples), (2) JEOL JSM 840 SEM equipped with a Link 10000 energy dispersive X-ray spectrometry system (SEM-EDS; four dust samples), and (3) Quanta 200 FEI environmental SEM equipped with a EDAX energy dispersive X-ray spectrometry system (ESEM-EDS; seven dust samples and six PT samples). All the EDS chemical analyses were calculated using the ZAF matrix correction method (Goldstein et al., 2003). Prior to the examination of dust particles by either electron probe microanalysis or by SEM they were removed from the filter by sonication in ethanol (Kalderon, 2005). ESEM analysis was conducted directly on tenth of a filter without coating, taking advantage of the ESEM option to work in a low vacuum mode (w1 Torr). At this low vacuum the filter remains stable during measurements. During the microscopic analysis a few fields of 50  50 mm were randomly chosen in each filter. Each particle detected in a field was chemically analyzed and its size and morphological characteristics

Fig. 2. Air mass backward trajectories calculated for 24 h during dust storms sampled in this study for the different synoptic systems: blue – Red Sea trough; orange – Sharav cyclone; red – cold depression; and calculated for 48 h during Persian trough synoptic systems sampled in this study; green – deep Persian trough; and violet – shallow Persian trough.

3966

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

were recorded. Elemental ratios, calculated from the chemical composition, were used to identify the mineralogical composition by comparison with known structural formulae (Weaver and Pollard, 1973; Deer et al., 1992; Sandler, 1992). Since most of the particles were mixtures of several minerals, a distribution scale (5– 1) of mineralogical composition was established, whereas ‘‘5’’ marks the most abundant mineral in the mixture and ‘‘1’’ – the least abundant one (Kalderon, 2005). Special attention was paid to heavy metal-rich particles using backscatter mode. Therefore, there is some positive discrimination for heavy metal-rich particles. Since the main tool for mineralogical analysis was ESEM-EDS, great care was devoted to error evaluation as described in the supplementary data (Goldstein et al., 2003). The details of the meteorology analysis are also outlined in the supplementary material. 3. Results and discussion 3.1. Classification of sampling events Thirteen dust storms and five PT events were sampled in this study and were classified into five categories according to the synoptic system (Fig. 1). Three dust storms were sampled during Red Sea trough conditions (RS, 2/28-3/1/2002, 3/11-12/2002, 11/2223/2003, 14 filters); seven dust storms were sampled during Sharav cyclone conditions (SC, 4/30-5/1/2001, 5/13-15/2001, 3/18-20/ 2002, 2/17-18/2003, 4/2-3/2003, 4/4-7/2003, 5/29-31/2003, 34 filters); three storms were sampled during cold depression synoptic conditions (CD, 3/17-19/2003, 4/24-25/2003, 1/22-26/ 2006, 28 filters); two deep mode events of Persian trough synoptic conditions were sampled (deep PT, 7/8-10/2003, 9/4-5/2003, 10 filters); and, three shallow modes of Persian trough were sampled (shallow PT, 8/1-2/2003, 8/22-24/2003, 8/25-27/2003, 20 filters). The 24 and 48 h backward trajectories of the air masses that were transported to Jerusalem during the sampling events were calculated (Fig. 2). 3.2. Mineralogical characterization of desert dust according to synoptic systems Almost all the collected and analyzed particles were smaller, or at least one of their dimensions was shorter, than 2.5 mm (Fig. 3).

n = 3176 50.0%

40.0%

30.0%

20.0%

10.0%

.0% 0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

More

Grain size (µm) Fig. 3. Grain size distribution (in percent) of suspended dust particles, based on scanning electron microscope image analysis of 3176 particles from 11 filters presenting the three dust transporting synoptic systems.

This result is based on measurements of 3176 dust particles. Similar size distribution pattern of suspended particles was obtained previously from much smaller number of particles (Alpert and Ganor, 2001; Falkovich et al., 2001). A large, but similar variety of minerals was observed in all synoptic conditions (Fig. 4). Fig. 4a–c summarizes the mineralogical composition of the suspended dust particles smaller than 2.5 mm sampled during the three synoptic systems. The major minerals of the suspended desert dust were illite–smectite, calcite, gypsum, quartz, dolomite, kaolinite, palygorskite, apatite, halite, and Fe oxides. The minor minerals included illite, smectite, Ti oxides, ilmenite, K-feldspar, plagioclase, barite, talc, monazite, celestite, zircon, pyroxene, amphibole, mica, chlorite, nontronite, lizardite, pyrite, and various sulfates. In addition, organic matter was identified in a few samples. In a few samples there was an excess of up to 5% (concentration beyond the known range of the element in the mineral formula) of Na, Mg, S, Cl, K and Al. Various trace metals (Pb, Cu, Mn, Zn, Au, and Mo) were also observed. Some of the minerals were present in all dust events, while others were characteristic of a specific synoptic type. Illite–smectite and calcite were the most dominant, along with gypsum, dolomite and apatite, and they were present in all samples. Illite–smectite and calcite had similar concentrations except in CD samples where illite–smectite was twice more abundant than calcite (Fig. 4c). In addition, halite was slightly more abundant in CD samples, due probably to the more maritime nature of the air masses transported by this synoptic system. Heavier minerals (i.e., zircon, barite, monazite, and celestite) were also more common in CD samples, probably because of the stronger winds generated by this synoptic system (Fig. 2). Relatively high concentrations of kaolinite and quartz were typical for SC (9% and 13%, respectively) (Fig. 4a–c). The higher concentrations of kaolinite and quartz in SC samples might suggest contribution from Nubian-type sandstone outcrops exposed in the Qattara Depression, Ghard Abu Muhari or Wadi Langeb areas (Geographical Section, 1941; Bentor, 1966; Prospero et al., 2002). Palygorskite was characteristic of RS (appeared in 15% of the particles) in accord with a previous observation (Ganor, 1991). This palygorskite was probably derived from paleolacustrine sediments (Velde, 1995) exposed at various depressions in the Arabian Peninsula and Jordan that lie along the air mass pathways of RS (Geographical Section, 1941; Fig. 2). Relatively high concentrations of illite were observed in CD samples (3%). Its origin might be attributed to weathered granites, as illite grows on the weathered surfaces of muscovite or biotite in contact with K-feldspar (Velde, 1995), and/or to Paleozoic sandstones that were deeply buried (Bentor, 1966). Despite the fact that Ganor (1991) analyzed settled dust and the current research focuses on suspended dust, a few interesting observations can be made. (1) This study shows that illite–smectite is the most dominant clay mineral for all synoptic systems, while Ganor (1991) reported it as an abundant mineral only in dust arriving from Tibesti and Saudi Arabia (the term ‘‘illite–smectite’’ appears in the old literature as ‘‘montmorillonite’’); (2) both studies agree that palygorskite is indicative for dust from Saudi Arabia sources; (3) according to Ganor (1991) illite makes up 70–95% of the clay mineral composition in dust originating from Chad and Libya, which is far beyond the measured concentrations in the current study; and (4) Ganor (1991) reported that the abundance of kaolinite ranges between 15 and 50% of the clay minerals in dust arriving from Tibesti and Saudi Arabia, whereas in this study only low concentrations were detected, and only in SC samples. In summary, the mineralogy of suspended dust, in contrast to the settled dust studied by Ganor (1991) is not indicative (with the exception of palygorskite) to the sources of the dust and the synoptic system that transports it.

a

Red Sea trough PM2.5

300

5 4 3 2 1

Number of particles

250

200

150

100

50

b

More

Albite

K-feldspar

Zn

Mn

Pb

Cu

Ilmenite

Ti-oxides

Fe-oxides

Excess of Na

Halite

Apatite

clays

Illite

Smectite

Kaolinite

Palygorskite

Dolomite

Quartz

Gypsum

Calcite

Illite-Smectite

0

Sharav cyclone PM 2.5

70

5 4 3 2 1

Number of particles

60 50 40 30 20 10

c

Cold depression PM2.5

450

5 4 3

400

2 1

350

Number of particles

More

Albite

K-feldspar

Zn

Mn

Cu

Pb

Ilmenite

Ti-oxides

Fe-oxides

Excess of Na

Halite

Apatite

clays

Smectite

Illite

Palygorskite

Kaolinite

Dolomite

Quartz

Gypsum

Calcite

Illite-Smectite

0

300 250 200 150 100 50

More

Albite

K-feldspar

Zn

Mn

Cu

Pb

Ilmenite

Ti-oxides

Fe-oxides

Excess of Na

Halite

Apatite

clays

Smectite

Illite

Palygorskite

Kaolinite

Dolomite

Quartz

Gypsum

Calcite

Illite-Smectite

0

Fig. 4. Mineralogical composition based on chemical point analyses of PM2.5 collected during dust storms under different synoptic conditions: (a) Red Sea trough; (b) Sharav cyclone; and (c) cold depression. Legend: 5–1 ¼ maximum to minimum abundance of minerals in the mixed particles. ‘‘More’’ ¼ talc, barite, organic matter, monazite, celestite, zircon, pyroxene, amphibole, micas, chlorite, excesses of Mg, S, Cl, K and Al, nontronite, lizardite, plagioclase, pyrite, Au, Mo, and sulfates.

3968

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

a

Deep Persian Gulf trough 180

5 4 3 2 1 0

160

Number of particles

140 120 100 80 60 40 20 0 Na Mg

b

Al

Si

P

S

Cl

K

Ca

Ti

V

Cr

Mn Fe

Ni

Cu

Zn

Ba

Pb o.m.

Shallow Persian Gulf trough 80

5 4 3 2 1

70 60

Number of particles

Co

50 40 30 20 10 0 Na Mg Al

Si

P

S

Cl

K

Ca

Ti

V

Cr Mn Fe

Ni Cu Zn Se Cd Ba Au Pb o.m.

Fig. 5. Chemical point analysis of aerosols collected during Persian trough synoptic conditions: a) deep mode; b) shallow mode. Legend: 5–1 ¼ maximum to minimum degrees of elemental dominance in a mixture. (o.m. ¼ organic matter). Note that there is a positive discrimination for heavy metal-rich particles due to the ESEM methodology used in the study. They seem to be more abundant than they actually are.

3.3. Major element composition of dust samples according to synoptic systems The major element composition of bulk samples collected during dust storms not only supports the microscopy point analysis, but it also provides some quantitative estimates of the different compounds. The significantly higher Ca and Mg concentrations and Ca/Al ratio in the L1 (0.5 M HNO3 leach) relative to the L2 fraction (the residue of L1 dissolved in concentrated HF and HNO3) indicate that a separation between carbonates and silicates was indeed achieved by the two-stage leaching process (supplementary material). Moreover, Ca/Al values for the various synoptic types were different. They were approximately 26 in L1 of RS samples (Arabian sources), and about eight in both SC and CD (North African sources; supplementary material). This difference reflects the higher Al concentrations in the L1 fraction of dust from North African sources. In the L2 fraction Ca/Al ratio is approximately 0.25, 0.2 and 0.1 in RS, SC and CD, respectively (supplementary

material), implying that Al-silicates of Arabian origin contain less Al relative to Ca. This might reflect the fact that North African dust is more felsic than the Arabian dust. Hence, Ca/Al values of the L2 fraction reflect the ESEM observation that SC samples contain more kaolinite (Al-rich clay) while CD samples are enriched in illite– smectite relative to RS (Fig. 4). The Ca/Mg ratio in L1 varies in dust according to synoptic systems, being approximately 18 in RS samples and eight in SC and CD samples (supplementary material). These differences do not reflect different calcite to dolomite ratio between the RS and the other two synoptic systems, as the observed abundance of calcite to dolomite in dust from all three synoptic systems was around 9:1 according to our microscopic data (Fig. 4). On the other hand, in the Al-silicates (L2 fraction) Ca/Mg values are very similar in dust samples from all synoptic types and are approximately one. Mg/Al values in the L2 fraction vary between w0.25 in RS samples, to w0.16 in SC samples and to w0.08 in CD (supplementary material). The variations in the L2 Mg/Al values reflect differences in clay

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

composition as observed by ESEM, because RS samples have higher concentrations of palygorskite relative to the other synoptic systems (Fig. 4a). The Na/Al values of the L1 fraction are 0.18 in RS and 0.09 in SC and CD, although in RS and SC samples the correlations are very weak (supplementary material). The higher Na/Al ratio in RS samples is consistent with the ESEM observations that halite and mainly excess of Na, whose source is still unknown, are more abundant in RS samples than in the other samples (Fig. 4). In the L2 fraction the correlations are also very weak, except for the CD samples (R2 ¼ 0.94), which infer a uniform composition of the Alsilicates that contribute Na. The range of Na/Al values in the L2 fraction is 1–3% for all three synoptic types reflecting the dominance of illite–smectite. This range is characteristic of clays formed by pedogenic processes, where Na is depleted relative to Al (Velde, 1995). Therefore, the Na/Al ratio in the L2 fraction of the suspended dust samples indicates the ubiquity of clays in the Al-silicate fraction of the dust. Again, this is in accordance with our mineralogical composition data (Fig. 4), where illite–smectite is the most dominant mineral in all samples. The extent of anthropogenic pollution transported by suspended dust has been reported elsewhere (Erel et al., 2006). Most samples were enriched (EF  5) (Sutherland, 2000) in Ni, Cu, Zn and Pb: EFNi ¼ 29, EFCu ¼ 39, EFZn ¼ 12 and EFPb ¼ 102 in the L1 fraction, and EFNi ¼ 25, EFCu ¼ 7, EFZn ¼ 4 and EFPb ¼ 9 in the L2 fraction. The fact that the L2 fraction of many dust samples was polluted suggests that they contain polluted soil particles, either from the Jerusalem area or from other polluted regions lying along the path of the storms. These polluted soils should be outside the principal sources of dust which according to Prospero et al. (2002) are located in pristine regions. Furthermore, small size (1.5 mm) particles made of heavy metals (e.g., Pb, Cu – supplementary material) were identified by ESEM mostly in SC and CD samples which carry dust from North Africa (Fig. 2). These particles are of anthropogenic origin and they might reflect smelting activities, an ubiquitous bustle in the Cairo Metropolitan area (Abu-Allaban et al., 2002). 3.4. Characterization of particles during Persian trough During the two deep mode PT events the sampling station was beneath the thermal inversion base and within the convective boundary layer, while the sampling of the three shallow mode PT events was conducted above the convective boundary layer, i.e., above the thermal inversion base. The major and trace element bulk composition of the L1 fraction of these two modes of PT events was different (Erel et al., 2007). This difference is best demonstrated by their enrichment factor values (supplementary material). Deep mode PT samples were highly enriched relative to Al in Na, Mg, and Ca but not in Fe (129  124, 47  33, 61  38, and 2  1, respectively), while shallow mode PT samples were mostly enriched in Ca, less enriched in Na and Mg and were not enriched in Fe (44  20, 10  9, 11  5 and 1  0, respectively). The overall chemical composition of the inorganic fraction, obtained by ESEM (Fig. 5) was similar to the one obtained by ICP-MS from the L1 fraction in both PT modes (Erel et al., 2007; supplementary material). However, ESEM data indicate additional major findings: (a) the aerosols contain S, Si and Cl not identified by ICP-MS (Fig. 5); (b) Na is much more abundant than Cl, hence it cannot come from sea salt; (c) in many cases, Na is either accompanied by excess S or cannot be related to any measured element; and (d) excess S relative to the structural formulae of gypsum or anhydrite could be related to particulate ammonium sulfate known to be emitted from anthropogenic sources in the Eastern Mediterranean during the summer months (Luria et al., 1996; Wanger et al., 2000; Lelieveld et al., 2002). Indeed, Pb isotopic composition of the same samples

3969

indicated European sources (Erel et al., 2007). The major minerals in the PT samples are clays, halite, gypsum, quartz, and calcite (Fig. 5). However, the most striking finding about the nature of PT aerosols is that, in contrast to desert dust, even their inorganic fraction has to a large extent non-natural, non-mineral composition (Fig. 5). Furthermore, in all PT samples there is an excess of several major elements (Na, Mg, Al, S, Cl, Mn, Fe – concentration beyond the known range of the element in mineral formulae) up to 50%, while in desert dust only a few samples have up to 5% excess of Na, Mg, Al, S, Cl, and K. Several metals (Cr, Co, Ni, Cu, Zn, Pb), which are usually traces in minerals, were detected as major constituents of many PT particles (Fig. 5; Erel et al., 2007). To our knowledge this is the first study to demonstrate the pervasive non-natural, anthropogenic origin of the ‘‘mineral’’ fraction of atmospheric particles transported over such long distances during several months every year. These particles affect the air quality and visibility of the entire Eastern Mediterranean region (Lelieveld et al., 2002). 4. Conclusions The current study is based on the integration of chemical bulk analysis of major and trace elements with chemical point analysis in order to characterize atmospheric aerosols and explore their relationships with the major synoptic systems dominating the Eastern Mediterranean region. 1. Regardless of the synoptic system, the suspended particles are mostly smaller than 2.5 mm, their morphology is not indicative, and each particle is a mixture of several mineralogical phases. 2. Under all synoptic conditions the suspended particles contain high levels of toxic metals. 3. There are several minor differences in the mineralogical and chemical composition of desert dust transported by the three different synoptic types (e.g., Red Sea trough samples have significantly higher Ca/Al and Ca/Mg in the carbonate and Mg/ Al in Al-silicate fraction than cold depression samples); however, in most aspects all three synoptic conditions carry dust with similar mineralogy and chemical composition in spite of the fact that the source regions are different. This contradicts findings of previous studies carried out on settled dust in Israel. 4. This study uses the same methodological tools for analyzing desert dust particles and aerosols originating in Eastern Europe, to provide evidence for the striking difference between the two kinds of particles. Whereas desert dust has a prominent natural composition, Eastern European aerosols are mostly anthropogenic, so that even their inorganic ‘‘mineral’’ fraction contains up to 50% non-natural load. Acknowledgments The authors wish to thank Mila Palchan and Vitaly Gutkin for providing invaluable assistance in understanding of the various ESEM applications. The assistance of Dror Stern, Reut Rabi, Rivka Nissan and Livia Katz of the Hebrew University in Jerusalem with the sampling process and laboratory work is greatly appreciated. The authors thank Olga Yoffe, Irena Segal, Natalya Teplyakov and Michael Dvorachek of the Geological Survey of Israel for assisting with chemical and SEM analysis. This work was supported by the Israeli Ministry of Environmental Protection fund. Appendix. Supplementary data Supplementary material associated with this article can be found in the online version, at doi:10.1016/j.atmosenv.2009.03.057.

3970

B. Kalderon-Asael et al. / Atmospheric Environment 43 (2009) 3963–3970

References Abu-Allaban, M., Gertler, A.W., Lowenthal, D.H., 2002. A preliminary apportionment of the sources of ambient PM10, PM2.5, and VOCs in Cairo. Atmospheric Environment 36, 5549–5557. Alpert, P., Ganor, E., 2001. Sahara mineral dust measurements from TOMS: comparison to surface observations over the Middle East for the extreme dust storm, March 14–17, 1998. Journal of Geophysical Research 106 (D16), 18,275–18,286. Alpert, P., Ziv, B., 1989. The Sharav cyclone: observations and some theoretical considerations. Journal of Geophysical Research 94, 18,495–18,514. d’Almeida, G., 1986. A model for Saharan dust transport. Journal of Climate and Applied Meteorology 25, 903–916. Bentor, Y.K., 1966. The Clays of Israel; Guide-book to the Excursions International Clay Conference, Jerusalem. Bitan, A., Sa’aroni, H., 1992. The horizontal and vertical extension of the Persian Gulf pressure trough. International Journal of Climatology 12, 733–747. Buat-Menard, P., Chesselet, R., 1979. Variable influence of the atmospheric flux on the trace metal chemistry of oceanic suspended matter. Earth and Planetary Science Letters 42, 399–411. Carlson, T.N., Prospero, J.M., 1972. The large-scale movement of Saharan air outbreaks over the northern equatorial Atlantic. Journal of Applied Meteorology 11, 283–297. Chester, R., Baxter, G.G., Behairy, A.K.A., Connor, K., Cross, D., Elderfield, H., Padgham, R.C., 1977. Soil-sized eolian dusts from the lower troposphere of the eastern Mediterranean Sea. Marine Geology 24, 201–217. Chester, R., Nimmo, M., Keyse, S., 1996. The influence of Saharan and Middle Eastern desert-derived dust on the trace metal composition of Mediterranean aerosols and rainwater: an overview. In: Guerzoni, S., Chester, R. (Eds.), The Impact of Desert Dust Across the Mediterranean. Kluwer. Crouvi, O., Amit, R., Enzel, Y., Porat, N., Sandler, A., 2008. Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel. Quaternary Research 70, 275–282. Dayan, U., 1986. Climatology and back trajectories from Israel based on synoptic analysis. Journal of Climate and Applied Meteorology 25, 591–595. Dayan, U., Heffter, J., Miller, J., Gutman, G., 1991. Dust intrusion events into the Mediterranean Basin. Journal of Applied Meteorology 30, 1185–1199. Dayan, U., Levy, I., 2005. The influence of seasonal meteorological conditions and atmospheric circulation types on PM10 and visibility in Tel-Aviv, Israel. Journal of Applied Meteorology 44, 606–619. Dayan, U., Lifshitz-Goldreich, B., Pick, K., 2002. Spatial and structural variation of the atmospheric boundary layer during summer in Israel - Profiler and rawinsonde measurements. Journal of Applied Meteorology 41, 447–457. Deer, W.A., Howie, R.A., Zussman, J., 1992. An Introduction to the Rock Forming Minerals. Longman Scientific & Technical, Hong-Kong. Erel, Y., Dayan, U., Rabi, R., Rudich, Y., Stein, M., 2006. Trans boundary transport of pollutants by atmospheric mineral dust. Environmental Science & Technology 40, 2996–3005. Erel, Y., Kalderon-Asael, B., Dayan, U., Sandler, A., 2007. European atmospheric pollution imported by cooler air masses to the Eastern Mediterranean during the summer. Environmental Science & Technology 41, 5198–5203. Falkovich, A.H., Ganor, E., Levin, Z., Formenti, P., Rudich, Y., 2001. Chemical and mineralogical analysis of individual mineral dust particles. Journal of Geophysical Research 106, 18,029–18,036. Formenti, P., Andreae, M.O., Andreae, T.W., Ichoku, C., Schebeske, G., Kettle, J., Maenhaut, W., Cafmeyer, J., Ptasinsky, J., Karnieli, A., Lelieveld, J., 2001. Physical and chemical characteristics of aerosols over the Negev Desert (Israel) during summer 1996. Journal of Geophysical Research – Atmospheres 106, 4871–4890. Ganor, E., 1991. The composition of clay minerals transported to Israel as indicators of Saharan dust emission. Atmospheric Environment 25A, 2657–2664. Ganor, E., Foner, H.A., 1996. The mineralogical and chemical properties and the behaviour of aeolian Saharan dust over Israel. In: Guerzoni, S., Chester, R. (Eds.), The Impact of Desert Dust Across the Mediterranean. Kluwer Academic Publishers, Netherlands, pp. 163–172. Ganor, E., Foner, H.A., 2001. Mineral dust concentrations, deposition fluxes and deposition velocities in dust episodes over Israel. Journal of Geophysical Research-Atmospheres 106, 18,431–18,437.

Ganor, E., Foner, H.A., Brenner, S., Neeman, E., Lavi, N., 1991. The chemical composition of aerosols settling in Israel following dust storms. Atmospheric Environment 25A, 2665–2670. Ganor, E., Mamane, Y., 1982. Transport of Saharan dust across the Eastern Mediterranean. Atmospheric Environment 16, 581–587. Geographical Section G.S., 1941. The Near and Middle East. War Office, UK. Goldstein, J.I., Newbury, D.E., Joy, D.C., Lyman, C.E., Echlin, P., Lifshin, E., Sawyer, L.C., Michael, J.R., 2003. Scanning Electron Microscopy and X-Ray Microanalysis. Kluwer Academic/Plenum Publishers, New York. Israelevich, P.L., Ganor, E., Levin, Z., Joseph, J.H., 2003. Annual variations of physical properties of desert dust over Israel. Journal of Geophysical Research 108 (D13), 4381. doi:10.1029/2002JD003163. Kalderon, B., 2005. Mineralogical and chemical characterization of aerosols transported to Israel. M. Sc. Thesis, The Hebrew University of Jerusalem. Koch, J., Dayan, U., 1992. A synoptic analysis of the meteorological conditions affecting dispersion of pollutants emitted from tall stacks in the coastal plain of Israel. Atmospheric Environment 26A, 2537–2543. Lelieveld, J., Berresheim, H., Borrmann, S., Crutzen, P.J., Dentener, F.J., Fischer, H., Feichter, J., Flatau, P.J., Heland, J., Holzinger, R., Korrmann, R., Lawrence, M.G., Levin, Z., Markowicz, K.M., Mihalopoulos, N., Minikin, A., Ramanathan, V., De Reus, M., Roelofs, G.J., Scheeren, H.A., Sciare, J., Schlager, H., Schultz, M., Siegmund, P., Steil, B., Stephanou, E.G., Stier, P., Traub, M., Warneke, C., Williams, J., Ziereis, H., 2002. Global air pollution crossroads over the Mediterranean. Science 298, 794–799. Luria, M., Peleg, M., Sharf, G., Siman Tov-Alper, D., Spitz, N., Ben Ami, Y., Gawii, Z., Lifschitz, B., Yitzchaki, A., Seter, I., 1996. Atmospheric sulfur over the east Mediterranean region. Journal of Geophysical Research 101D, 25,917–25,930. Mahowald, N.M., 2007. Anthropocene changes in desert area: sensitivity to climate model predictions. Geophysical Research Letters 34, L18817. doi:10.1029/ 2007GL030472. Matvev, V., Dayan, U., Tass, E., Peleg, M., 2002. Atmospheric Sulfur flux rates to and from Israel. Science of the Total Environment 291, 143–154. Moulin, C., Lambert, C.E., Dayan, U., Masson, V., Ramonet, M., Bousquet, P., Legrand, M., Balkanski, Y.J., Guelle, W., Marticorena, B., Bergametti, G., Dulac, F., 1998. Satellite climatology of African dust transport in the Mediterranean atmosphere. Journal of Geophysical Research 103 (D11), 13,137–13,144. Prospero, J.M., Ginoux, P., Torres, N., Sharon, E., Thomas, E., 2002. Environmental characterization of global sources of atmospheric soil dust identified with the nimbus 7 total ozone mapping spectrometer (TOMS) absorbing aerosol product. Review of Geophysics 40. 1002. doi:10.1029/2000RG000095. Rahn, K.A., 1975a. Chemical composition of the atmospheric aerosol. A compilation I. Extren 4, 286–313. Rahn, K.A., 1975b. Chemical composition of the atmospheric aerosol. A compilation II. Extren 4, 639–667. Sandler A., 1992. The stratigraphy and the depositional environment of the clastic unit in the Turonian. Ph.D. Thesis, The Hebrew University of Jerusalem. Schu¨tz, L., 1980. Long range transport of desert dust with special emphasis on the Sahara. Annals of the New York Academy of Science 338, 515–532. Singer, A., Ganor, E., Dultz, S., Fischer, W., 2003. Dust deposition over the Dead Sea. Journal of Arid Environments 53, 41–59. Sutherland, R.A., 2000. Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii. Environmental Geology 39, 611–627. Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell Scientific Publications, London. Tegen, I., Lacis, A.A., Fung, I., 1996. The influence on climate forcing of mineral aerosols from disturbed soils. Nature 380, 419–422. Velde, B., 1995. Origin and Mineralogy of Clays: Clays and the Environment. Springer, Verlag, Berlin, Heidelberg. Wanger, A., Peleg, M., Sharf, G., Mahrer, Y., Dayan, U., Kallos, G., Kotroni, V., Lagouvardos, K., Varinou, M., Papadopoulos, A., Luria, M., 2000. Some observational and modeling evidence of long range transport of air pollutants from Europe towards the Israeli coast. Journal of Geophysical Research 105, 7177–7186. Weaver, C.E., Pollard, L.D., 1973. The Chemistry of Clay Minerals. Elsevier, Amsterdam. Yaalon, D.H., Ganor, E., 1979. East Mediterranean Trajectories of Dust-Carrying Storms from the Sahara and Sinai. In: Morales, C. (Ed.), Saharan Dust (Mobilization, Transport, Deposition). Wiley, pp. 187–193.