TRACE ELEMENT COMPOSITION OF THE EASTERN MEDITERRANEAN AEROSOLS: INDICATORS FOR DISTANT SOURCE REGIONS

Gulen Gullu, Ilhan Olmez, Gurdal Tuncel

Middle East Uniiversity, Dept. Environmental Engineering, 06531 Ankara, Turkey

Tubitak-Marmara Research Center, 41470 Kocaeli, Turkey

ABSTRACT

Approximately 700 atmospheric aerosol samples collected on the Mediterranean coast of Turkey were analyzed for 40 elements and ions to determine the source regions of pollutants measured in the Eastern Mediterranean atmosphere.  850 Mb climatology in the eastern Mediterranean have demonstrated that the most frequent flow are from north and northwest, which are the sectors that bring pollutants from industrialized European countries.  The difference between summer and winter flow patterns were not large enough to account for the seasonal variations in the observed concentrations of elements.  The factor analysis exercise performed on the data set has revealed that the eastern Mediterranean aerosol consists of five components, namely marine, crustal, local anthropogenic and distant anthropogenic.  Calculated potential source contribution functions indicated that the regions close to the basin, such as western parts of Turkey, Balkan countries, Greece and Italy are more effective source regions than the source regions in the Western Europe.

INTRODCTION

The Europe is an important source for the observed concentrations of pollutants in the regional seas around the continent, such as the Baltic Sea (Kikas et al., 1996), North Sea (Baeyens et al., 1990), Mediterranean Sea (Dulac et al., 1987), and the Black Sea (Hacisalihoglu et al., 1992).  Naturally, the presence of such a strong source has significant impact on the forests and lakes in the regions surrounding Europe.

Experimental and modeling studies performed in the region showed that the constituents of aerosols and precipitation are affected from two different source regions.  One of these regions is the Europe and the other one is the North Africa (Ganor and Mamane, 1982).  Transport of pollutants from Europe results in relatively acidic rain with high concentrations of ions like SO4=, NO3- and aerosol mass which is enriched in chalcophilic elements associated with anthropogenic activities.  On the other hand, transport of air masses from North Africa is expected to result in relatively clean air with rain pH higher than 5, owing to CaCO3 which is abundant in Saharan dust and aerosols which is highly enriched with lithophilic elements .

Although chemical composition of Western Mediterranean precipitation and aerosols had been fairly well characterized, data is extremely scarce on the chemical composition of the Eastern Mediterranean precipitation and aerosols.  In 1992 an atmospheric monitoring station was established in the Mediterranean coast of Turkey to determine atmospheric concentrations and calculate the deposition flux of elements in the eastern Mediterranean as well as to identify their sources and source regions.

 

METHODS

Approximately 700 aerosol samples were collected at a permanent station located approximately 20 km to the west of the town of Antalya, in the Mediterranean coast of Turkey, between December 20, 1991 and January 15, 1994.  The area with a diameter of 20 km around the station was free of any point sources and large settlement areas.

SO4=, NO3-, Cl- were determined by ion chromatography, NH4+ by spectrometry, Ca++, K+, Mg++ and Na+ by flame atomic absorption spectrometry and 35 trace elements by graphite furnace atomic absorption spectrometry (GFAAS) and instrumental neutron activation analysis.  Details of the sampling and analytical procedures were given elsewhere (Al Momani et al., 1995).

RESULTS and DISCUSSION

Since regions with different emission characteristics surround the Mediterranean Basin, the composition of particles in the Eastern Mediterranean is determined by transport frequency from these regions.  The flow pattern in the Eastern Mediterranean atmosphere is given in Figure 1.  The 850 Mb transport rose given in the figure is obtained from daily backtrajectory calculations over a period of 4 years between 1992 and 1995, using the ECMWF isentropic backtrajectory model.

Text Box:

Since the Mediterranean basin is surrounded by regions with different emission characteristics.  Transport from different wind sectors is expected to bring different types of aerosols to our sampling site. Four main source areas were broadly identified and related to trajectory sectors: (1) north-northwest Sectors include trajectories originating from Ukraine, Central Russia, Europe and Western Anatolia. This group of trajectories is expected to bring pollutant from industrialized European countries and intense and uncontrolled industrial emissions from Ukraine and central Russia. Approximately 47% of trajectories were in these sectors. (2) West-Southwest Sectors include trajectories originating and/or passing through Mediterranean Sea and northern part of Africa. Since this group of trajectories pass very close to north Mediterranean countries they can carry pollution from these areas as well as marine aerosols generated on the surface of the Mediterranean sea though bubble-bursting process. Approximately 30% of the trajectories have this origin. (3) Trajectories from south-southeast sectors transport Saharan dust and crustal material from the arid regions of Middle East and Arabian Peninsula. However only 7% of the trajectories calculated in three years were in these sectors. (4) East-northeast sectors include trajectories originating from Common Wealth of Independent States and crossing Eastern Anatolia before reaching the Antalya monitoring site. Since most of the countries which fall in these sectors are less industrialized compared to countries in North and Northwest sectors, this group of trajectories are not expected to transport pollution derived material but might be rich in crustal particles. Approximately 17% of the trajectories have an origin within these sectors. 

The study of the seasonal and annual variations in the discussed wind frequency distribution have revealed that there are some differences from one year to another and from one season to another, but these differences are generally too small to explain seasonal differences observed in the concentrations of measured parameters.

A factor analysis was performed to identify components of the aerosols measured in the Eastern Mediterranean atmosphere.  The results are given in Table 1.  Four interpretable factors with eigenvalues larger than unity were extracted.  The first factor was loaded with crustal elements and is clearly a crustal factor.  The second factor included elements and ions such as Se, Zn, NO3, nss-SO42- and NH4+ and identified as transported pollution.  Factor 3 was a marine factor loaded with elements lik Na, Cl and Br.  The fourth factor was heavily loaded with As and Sb and identified as local pollution.

Potential source contribution functions (Cheng et al., 1993) were calculated to determine the most likely source regions that contribute to the observed concentrations of elements.  Although source regions for individual elements do show differences, the general feature that is common for all anthropogenic elements was the close proximity of the potential source regions to the Eastern Mediterranean basin.  The most likely source areas for pollution-derived elements in the Eastern Mediterranean atmosphere were the western parts of Turkey, Bulgaria, Romania, Greece and Italy.   The Western European countries such as Germany, France and UK where emissions are higher do not have significant contribution on the observed concentrations of pollution-derived elements in the Eastern Mediterranean atmosphere, because particles bearing thee elements are scavenged out during long-range transport from western Europe to the Eastern Mediterranean.

Text Box: Table 1. Factor analysis results Factor 1 Factor 2 Factor 3 Factor 4 Communality Na 0.94 0.88 Mg 0.52 0.67 0.72 Al 0.94 0.88 Cl 0.94 0.88 K 0.63 0.26 0.46 Sc 0.97 0.94 V 0.62 0.63 0.78 Cr 0.41 0.25 0.25 0.27 Fe 0.96 0.92 Co 0.76 0.58 Zn 0.80 0.64 As 0.80 0.64 Se 0.88 0.77 Br 0.93 0.87 Sb 0.26 0.78 0.65 La 0.97 0.94 Ce 0.96 0.92 NO3- 0.26 0.79 0.69 nss-SO4= 0.83 0.69 NH4+ 0.81 0.66 % variance 42.00 15.50 12.60 10.20 80.30 REFERENCES

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