INCREASING TREND IN DUST CLOUD INTRUSIONS FROM THE SAHARA OVER ISRAEL. Department of Geophysics and Planetary Sciences, Tel Aviv University

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1 INCREASING TREND IN DUST CLOUD INTRUSIONS FROM THE SAHARA OVER ISRAEL Eliezer Ganor, Amnon Stupp, Pinhas Alpert, Isabella Osetinsky Department of Geophysics and Planetary Sciences, Tel Aviv University IUGG XXIV 2007 Perugia, Italy

2 Introduction Israel experiences periodic intrusions of natural mineral dust clouds from the Arabo-African region. The natural contribution of aerosols from Dust Events (DE) can increase PM10 to 4000 mcgr/m 3 half-hour average, a hundred times the concentration on clean days. Analysis of this data may help explain the meteorological and physical processes involved in the Dust phenomena.

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4 Methodology Observations and measurements of mineral dust were recorded over the 49 year period 1958/9-2005/2006. Dust was identified by visibility of less than 5000 meter and the presence of yellow-orange desert dust in rain-water. Measurements of aerosols with diameter less than 10 micron (PM10) were recorded from 1995 to 2006 by TEOM series 1400a Ambient Particulate (PM-10) Monitor in Tel-Aviv. Dust Events were defined for automatic detection with a triplethreshold algorithm : at least 3 continuous hours with PM10>100 mcgr/m^3, and a maximum reading of PM10>180 mcgr/m^3 during the period.

5 Fig. 1 : The number of days with DE in Tel-Aviv per year has increased with a slope of 2.4 days per decade, from 18 days in 1962 to 40 days in 2006 (16 to 26 smoothed fit).

6 Fig. 2 Monthly Average Dust Days Dust events are most common during March-April Number of DE days each month August September October November December January Ferbruary March April May June July Number of Dust Days

7 Fig. 3 : Probability of Rain given Dust and Rain Probability for Over these 42 year for 101 dates if there was Dust on these dates there was always Rain

8 Table 1 : The Synoptic Systems bringing DE over the Easterm Med. Were mostly Cyprus Lows (30.93%), Red Sea Troughs (22.98%), and Highs (22.73%). For

9 Fig. 4 : Trends in frequency of Synoptic System types during DE annual frequencies (solid), 5-y running averages (dotted), and linear trends (bold dashed). A+B+G: Sharav Lows and Winter Lows (WL). C: Highs. Type D: Red Sea Troughs. Dust days a) Types A+B+G 0.2 d/10y Dust days Dust days b) Types C 0.4 d/10y c) Types D 2.2 d/10y Dust days d) Types E -0.3 d/10y Dust days 5 e) Type F 0.3 d/10y Y E A R S

10 Fig. 5 : Most DE were measured to have short durations of 3-8 hours. A few lasted for up to 105 hours.

11 Fig. 6 : Most DE were observed to begin in Tel-Aviv between 5:00 and 8:00, and ended between 9:00 and 14:00 Beginning of Dust Events at Tel-Aviv :00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Hour Ending of Dust Events at Tel-Aviv :00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 00: Hour 00:00

12 Results Personal observations ) The number of days with Dust Events (DE) in Tel-Aviv per year has increased with a slope of 2.4 days per decade, from 18 days in 1962 to 40 days in 2006 (16 to 26 smoothed fit). (Fig.1) 2) Dust events are most common during March-April (Fig.2) 3) The presence of Dust increased the probability of Rain (Rain given Dust) to 100% for 101 dates of each of the 42 years (Fig. 3). 4) Rain after Dust is associated mainly with Cyprus Lows (30%), Red Sea Troughs (24%), and Highs (23%) (Table 1, Fig. 4). Automatic continuous measurements ) Duration of DE was 3 to 72 hours, most were in the range of 3-8 hours (Fig. 5). 6) Most DE begin in Tel-Aviv between 5:00 and 8:00, with the breaking of the inversion, and end between 9:00 and 14:00 (Fig. 6). 7) Total duration of DE in Tel-Aviv over a year was hours, average 339 hours/year. This is only 3.87% of the total 8760 hr in the year.

13 Results Personal observations ) The number of days with Dust Events (DE) in Tel-Aviv per year has increased with a slope of 2.4 days per decade, from 18 days in 1962 to 40 days in 2006 (16 to 26 smoothed fit). (Fig.1) 2) Dust events are most common during March-April (Fig.2) 3) The presence of Dust increased the probability of Rain (Rain given Dust) to 100% for 101 dates of each of the 42 years (Fig. 3). 4) Rain after Dust is associated mainly with Cyprus Lows (30%), Red Sea Troughs (24%), and Highs (23%) (Table 1, Fig. 4). Automatic continuous measurements ) Duration of DE was 3 to 72 hours, most were in the range of 3-8 hours (Fig. 5). 6) Most DE begin in Tel-Aviv between 5:00 and 8:00, with the breaking of the inversion, and end between 9:00 and 14:00 (Fig. 6). 7) Total duration of DE in Tel-Aviv over a year was hours, average 339 hours/year. This is only 3.87% of the total 8760 hr in the year. 8) The contribution of DE caused PM10 values to exceed the Israeli standard of 60 mcgr/m 3 /year in 6 of the 12 years. Using our DE identification algorithm we computed the average PM10 with and without DE. However, even without the DE contribution PM10 exceeded the level recommended by WHO (20 mcgr/m 3 /year) every year. PM2.5 values were over the Israeli recommended standard (15 mcgr/m 3 /year) even without DE. The contribution of DE to the annual PM10 average was 9%-27% (Fig. 7).

14 Fig. 7 : Annual PM10 (mcgr/m^3) with and without DE

15 Conclusions and Discussion 1) Increase in number of days with Dust Events each year 2) Causal connection between Dust and Rain, in the form of dust rains 3) Connection between Rain and Dust for the synoptic systems Red-Sea Trough, Cyprus Low, and Barometric High of 27%-88% for certain months 4) DE begin in Tel-Aviv between 5:00 and 8:00, with the breaking of the inversion 5) Synoptic change is apparent over the 50 years of Dust Events especially as an increase of Red-Sea Trough These results may indicate the effect of global or local change, such as desertification, on dust intrusions. The dust could in turn affect weather and climate through direct (redistribution of heat in the atmosphere) and indirect (cloud and precipitation) effects. DE statistics are relevant for transportation eg. through visibility, and for public health concerns.

16 Thank you for your attention

17 The contribution of DE caused PM10 values to exceed the Israeli standard of 60 mgr/m 3 /year in 6 of the 12 years. Using our DE identification algorithm we computed the average PM10 with and without DE. Even without DE contribution PM10 exceeded the level recommended by WHO (20 mgr/m 3 /year) every year.

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19 Total duration of DE in Tel-Aviv over a year was hours, average 339 hours/year out of total 8760 hr in a year

20 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture.

21 Monthly PM10 averaged for with and without DE, and DE contribution. The average monthly contribution of DE to PM10 was maximum for February, 37%

22 Table 1 : Frequency of probabilities for Rain, Dust, Dust and Rain, Rain given Dust. For There are 101 dates for which if there is Dust the probability for Rain is 100% (table 1 and fig.3)

23 Table 1 : The Synoptic Systems bringing DE over the Easterm Med. Were mostly Cyprus Lows (30.51%), Red Sea Troughs (23.62%), and Highs (22.74%). For

24 Dust Event Mineralogy Most dust particles in Israel are Calcium Carbonate, Calcite and Dolomite together are 71% by weight. Clay (Harsit) minerals are 2-4% of minerals. Analysis of single particles with electronic microscope shows Carbonate particles as aggregates with Clays, Salt, Sulfate, Nitrate, organic particles, and industrial urban pollution such as Diesel particles, and Carbon particles containing Zn, Cu, V, Ni

25 Average Bulk Mineralogical Composition of Settling Particles (Deposited Dust) in percent of weight in Israel Quartz Calcite Dolomite Feldspar Halite Gypsum CaCO3 = Calcite Dolomite=caMg(CO3)2 together

26 Average Bulk Clay Mineral Composition of Dust (%) in Israel Mineral Minimum Maximum Smectite Kaolinite Illite Paligoroskite

27 c) Aerosol classification based on their elemental composition (300 particles) at 1km above the sea; minerals (56%), sea salt (8%), aggregates of mineral with sea salt (16%) and sea salt with sulfate and nitrate (15%)

28 Bulk aerosol chemistry before, during and after dust storm 3 ) Before 200 Dust Storm Consentration SO4 NO3 Cl Mg Fe Na K Ca Al After

29 Bulk aerosol chemistry before, during and after dust storm 2 3) Before 1 Dust Storm Consentration Cu Ba Sr Mn Cr Cd Pb Zn V Ni After

30 3. Chemical composition Elemental and chemical analysis of single particles collected in flight on revealed that many particles consisted of: a) Aggregates of mineral dust and sea salt

31 b) The wet particles contained CaCO 3, NaCl and NaNO 3.