The chemical composition of rainwater over Büyükçekmece Lake, Istanbul

Atmospheric Research 71 (2004) 275–288

www.elsevier.com/locate/atmos

The chemical composition of rainwater over

Bqyqkcekmece Lake, Istanbul

Bertan BaYak, Omar Alagha*

Department of Environmental Engineering, Fatih University, Buyukcekmece, Istanbul, 34500, Turkey

Received 3 May 2004; accepted 13 July 2004

Abstract

In the present study, the precipitation near Bqyqkcekmece Lake, which is one of the important

drinking water sources of Istanbul city, was studied during October 2001–July 2002. Seventy-nine

bulk precipitation samples were collected at two sampling stations near the Lake (4182V35WN,28835V25WE and 4185V30WN, 28837V7WE). The study comprised the determination of H+, Cl�, NO3

�,

SO42�, NH4

+, Na, K, Mg, Ca, Al, Ba, Fe, Cu and Mn concentrations in bulk deposition rain event

samples. The average volume-weighted pH value was found to be 4.81, which points out that the rain

is slightly acidic. High sulfate concentrations were observed together with high H+ ion values. Sulfur

emissions were the major cause for the observed high hydrogen ion levels. On the basis of factor

analysis and correlation matrix analysis, it has been found that in this region, acid neutralization is

brought about by calcium rather than the ammonium ion. The varimax rotated factor analysis

grouped the variables into four factors, which are crustal, marine and two anthropogenic sources.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Bulk deposition; Acid precipitation; Air pollution in Istanbul; Rainfall chemistry

1. Introduction

Every day, enormous quantities of anthropogenic and natural material are dumped into

the atmosphere and a majority of the materials added to the atmosphere return to the

0169-8095/$ -

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* Corresp

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see front matter D 2004 Elsevier B.V. All rights reserved.

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onding author. Tel.: +90 212 8890810; fax: +90 212 8890906.

ress: [email protected] (O. Alagha).

B. BasSak, O. Alagha / Atmospheric Research 71 (2004) 275–288276

ground. Large quantities of oxides of sulfur and nitrogen are being emitted to the

atmosphere by the combustion of fossil fuels and industrial processes, and these gases are

being converted into strong acids (sulfuric and nitric), which lead to many areas

experiencing precipitation of very low pH values (Elsom, 1987; Al-Momani et al., 1997;

Granat et al., 1996). Environmental adverse effects of acid rain include changes in the

leaching rates of nutrients from plant foliage and soil nutrients, acidification of lakes and

rivers, effects on metabolism of organisms and corrosion of structures (Kelly et al., 1989;

Bard, 1999). In addition to that, acid rain is also responsible for reduction of visibility and

deterioration of historical structures especially by damaging the details on historic places

or sculptures (Elsom, 1987; Bierwagen et al., 2003). Man is also primarily responsible for

the enrichment of many trace elements now found in the atmosphere caused by the

combustion of fossil fuels, including such additives as the lead in gasoline, roasting of ores

for refining metals, processing of crustal materials for manufacturing cements, and burning

of waste materials (Baubel et al., 1994). Although acid rain and acidification of the

environment have emerged as environmental issues of increasing concern in the world,

there are very limited studies on precipitation chemistry in Turkey (Alagha and Tuncel,

2002; Samura et al., 2003; Kaya and Tuncel, 1997). Earlier studies indicate that the

rainwater of the region is slightly acidic. Potential source regions contributing to the

acidity of rainwater are Northern Europe and the industrial cities of Turkey, while sources

of neutralizing species include both local and remote areas such as Middle East and North

Africa (Elagha et al., 2001; Al-Momani et al., 1997; Gulsoy et al., 1999).

The objective of this study is first to evaluate the chemical composition of atmospheric

deposition around the Bqyqkcekmece Lake. These data are analyzed to obtain an idea

about the factors controlling the rain acidity. The method of enrichment factor, correlation

matrix and factor analysis are carried out to understand the relationship between the

acidifying species and basic species and sources of the chemical components in the

precipitation.

2. Experimental

2.1. Site description

Istanbul, located in the northern west of Turkey, is the most crowded city with a

population of about 10 million. It is also a world renowned tourist destination with unique

historic and aesthetic sites lying on two continents. Bqyqkcekmece Lake is located in a

suburban area, which is located 30 km away from the city centre. Two rainwater sampling

stations were selected near Bqyqkcekmece Lake away from the direct influence of local

anthropogenic pollution sources. One of the stations (station 1) was situated in the

Bqyqkcekmece Water Treatment Plant of ISKI (Water and Sewerage Administrative

Center of Istanbul) (41882V35WN, 28835V25WE), while other one (station 2) was situated atFatih University Campus (41885V30WN, 28837V7WE). The stations were about 5 and 10

km away from the Marmara Sea shore, respectively, and approximately at sea level. The

samplers were placed at 1 m above the ground. Fig. 1 illustrates the locations of the

sampling sites in the Bqyqkcekmece area.

Fig. 1. Location of Bqyqkcekmece Lake and sampling stations.

B. BasSak, O. Alagha / Atmospheric Research 71 (2004) 275–288 277

2.2. Sampling and analysis

Bulk rain samples were collected manually on a daily event basis to reduce the amount

of dust entering the sampler to the minimum. Although bulk sampling is not the preferred

sampling method for precipitation, still it is being used by some EMEP networks around

Europe (EMEP, 1966). The rain sampler used was a homemade one, simple, inexpensive,

and easy to use which consists of a high density polyethylene (HDPE) funnel of 50 cm

diameter, mounted inside a PP (polypropylene) bucket containing a 5-l HDPE bottle to

collect rain samples. The bottle was supported by Styrofoam to protect it from the spillage.

After the rain event finished, the 5 l collection bottle in the samplers was replaced by new

pre-washed one. The funnel was rinsed three times with de-ionized water before being

positioned again. During dry periods, samples were collected weekly by washing the

sampler funnel with 100 ml of de-ionized water. Sampling bottles were closed and brought

to the environmental engineering laboratory at Fatih University. The bottles were opened

and the samples were collected in a laminar flow cabinet, which provides a particle free

environment, in order to minimize contamination and obtain low blank values for better

detection limits.

De-ionized water was obtained from double distilled water that passed through a

Millipore water deionization system model 2010. The prepared de-ionized water has a

very good quality (resistance 18 MV).

Conductivity, pH, and NH4+ were measured in filtered rain samples right after the

sample collection. Volume of the rain was measured by comparing the sample in the

storage bottle with a pre-calibrated one to minimize the contamination. The samples were

filtered through 0.2 Am pore-sized cellulose acetate filter paper using a Sartorius

polystyrene filtration apparatus in order to separate the insoluble fraction of rainwater. For

pH measurements, a WTW Inolab level 1 pH meter, a WTW pH electrode SenTix 41 and

WTW buffer solutions were used. The measurement was carried out on a separate portion

(about 15 ml), which was discarded after measurement. About 250 ml of the sample was


stored in polypropylene bottles at 4 8C until analysis. The rest of the rain sample was

discarded. A radiometer Copenhagen conductivity meter and electrode was used for

conductivity measurements. Ammonium ion in rain samples was determined via a Jasco

V-530 spectrophotometer, using the direct Nesslerization method.

The insoluble fraction of the rain on the filter was digested by using an Ethos 900

Milestone Microwave digestion system and a mixture of commercial Suprapur grade

(Merck) hydrofluoric and nitric acid. Both the soluble and insoluble fractions of the

deposition were analyzed for Al, Mg, Fe, Cu, Ba, Mn, Na, K, and Ca using a Leeman Lab

model DRE, ICP-AES. Because H+, NH4+, Cl�, NO3

�, and SO42� are known to be

completely soluble in rainwater, these parameters were only measured in soluble fraction.

AVarian model 2010 HPLC coupled with a VYDAC 302 IC anion exchange column and a

Jasco UV/vis 875 detector were used for Cl�, NO3�, and SO4

2� analysis.

Blanks were collected and analyzed to be sure that contamination during the sampling

procedure and treatment of the samples was not significant, during both acid digestion and

sampling. Results of the blanks were used for blank correction. The detection limit of the

methods is taken to be three times the standard deviation of the blank results. Two different

standard reference materials (SRM), STM-1 (rock sample) and GSP-2 (rock sample) were

used for data quality assurance of the graphite furnace AAS and the ICP-AES method. The

SRM were treated and analyzed in the same way as the insoluble fraction of rain.

Differences between the measured and certified concentrations of the species were

insignificant ( pb0.001). Comparison of certified values and measured values are depicted

in Table 1. Calculated conductivity of rainwater was compared to measured conductivity

and no significant difference ( pb0.01) was observed.

Differentiation of sea-salt and non-sea-salt components is essential for many studies

of precipitation chemistry. The sea-salt fraction of a particular chemical constituent, Css,

of a precipitation sample was calculated from:

Css ¼ CSW=RefSWÞ � Ref sample

�

where CSW is the concentration of C in seawater, RefSW is the concentration of the

reference species (i.e. Na+ or Cl�) in seawater and Refsample is the concentration of the

Table 1

Comparison of the certified values of elements for two standard reference materials

Elements Units Found values Certified values Error %

GSP-2 STM-1 GSP-2 STM-1 GSP-2 STM-1

Ca % 1.45 0.77 1.50 0.78 3.33 1.28

K % 3.63 4.48 18.97

Mg % 0.57 0.06 0.58 0.06 1.72 0

Na % 2.01 2.06 2.42 14.87

Al % 7.34 8.27 7.88 9.74 6.85 15.09

Fe % 3.34 3.09 3.43 3.65 8.49 15.34

Ba Ag/l 1274.30 503.34 1340.00 560.00 4.92 10.11

Cu Ag/l 45.75 43.00 6.01

Mn Ag/l 1640.73 1700.00 3.48

Table 2

Chemical composition of precipitation (Aeqv/l) in Bqyqkcekmece

AMW AM GM STD MIN MAX SS

pH 5.10 5.36 5.16 1.43 3.30 7.76 0.28

Cl� 113.52 215.11 95.87 453.27 6.58 3229.62 17.36

NO3� 40.32 78.41 36.37 92.54 1.40 421.94 6.97

SO42� 195.68 231.89 69.93 312.37 5.46 1044.17 4.46

nssSO42� 35.39 218.92 105.68 303.34 2.79 1022.91 4.64

NH4+ 15.26 16.41 14.25 11.55 2.24 48.57 3.66

Ca 358.39 473.60 177.90 593.72 0.12 2010.16 3.71

K 69.26 73.60 39.25 113.99 4.79 628.00 8.83

Mg 242.37 259.84 120.60 354.80 4.98 1679.06 5.99

Na 73.87 113.13 55.08 186.87 0.02 1274.05 14.97

Al 1285.50 1302.98 556.67 2159.60 56.95 10,699.20 7.94

Ba 1.60 1.73 0.91 2.50 0.14 13.14 7.42

Fe 484.01 513.97 185.24 799.22 6.99 3729.52 6.62

Zn 6.45 8.23 5.13 9.38 1.04 32.84 4.00

Cu 4.42 4.19 4.23 2.09 2.43 9.96 3.46

AMW: Arithmetic weighted-mean, AM: arithmetic mean, GM: geometric mean, STD: standard deviation, MIN:

minimum, MAX: maximum, SS: standard skewness.


reference species in the precipitation sample. The non-sea-salt fraction Cnss is

calculated from:

Cnss ¼ CT � Css

where CT is the total concentration of C in the precipitation sample (Keene et al.,

1983).

Values of the total sulfate (SO42�) and non-sea-salt sulfate (nss-SO4

2�) concentrations

are depicted in Table 2 together with concentrations of other species.

3. Results and discussion

3.1. Comparison of the two sampling stations

Precipitation samples were collected at two sampling stations in order to figure out if

there are any local pollution sources impacting the air quality of the study site as well as to

minimize any possible data lost. No significant difference ( pb0.01 at the 95% confidence

level) between the concentrations of the species sampled in two different stations was

observed. Accordingly, data obtained from two sampling stations were treated together.

Comparison of the concentrations of the species collected at two sampling stations near

Bqyqkcekmece Lake is given in Fig. 2. Volume weighted average concentrations of the

species were given in Aeqv/l except pH, which is given in pH units. Values were given on

a logarithmic scale.

Fig. 2. Comparison of species concentrations of the two sampling sites.


3.2. pH analysis

Fig. 3 illustrates the temporal variation of pH in the period October 2001–July 2002.

The volume-weighted average pH value (based on H+ concentration and rain volume

calculations) for Bqyqkcekmece was 4.81, which is a slightly lower value than the widely

accepted background rain pH of 5.6 due to interaction between water droplets and carbon

dioxide in the atmosphere. The figure indicates that high precipitation acidity was

generally associated with winter samples, especially in the period November 16th–January

26th. The average pH for Istanbul was found to be 6.15 by Gulsoy et al. (1999) and the

average pH value for Kaynarca, which is a separate region outside of Istanbul, was 5.59

(Okay et al., 2002). The average pH value observed in Bqyqkcekmece was 5.58, which is

very similar to the corresponding value observed in Kaynarca. The highest acidity was

observed on 3rd of December 2001 with a pH of 3.30, and the lowest was on 7th of March

2002 with a pH of 7.76.

Fig. 3. Temporal variation of the pH from October 2001–July 2002 near Bqyqkcekmece Lake.


3.3. Ion concentrations in precipitation

The volume-weighted average concentrations of anions can be ordered in descending

order as follows SO42�NCl�NNO3

�. The main values of these anions were obtained as 195.6,

113.5, and 40.3 Aeqv/l, respectively. The cations volume weighted average concentrations

followed the pattern of Al3+NFe3+NCa2+NMg2+NNa+NK+NNH4+NCu2+NBa2+. Mean con-

centrations of cations were found to be 1285.5, 484.0, 358.4, 242.2, 73.8, 69.2, 15.2, 4.4

and 1.6 Aeqv/l, respectively. A similar trend of high Al3+NFe3+ was found in rainwater

samples collected by using a wet-only Anderson sampler at the Black sea region of Bartin

in Turkey (Alagha et al., 2002). The reason of this high Fe and Ca is that in the vicinity of

the sampling site there is a cement factory, and they are using calcium, silicon, iron and

aluminum rich ores rich explain the high concentration of these elements in rainwater.

Volume-weighted average concentrations of the species were also calculated and are

depicted in Table 2 beside the arithmetic mean, geometric mean, standard deviation,

minimum and maximum values.

As seen from Table 2, there are significant differences between arithmetic mean and

geometric mean values with high standard deviations for most of the measured parameters.

This is reported frequently by researchers such as Plasiance et al. (1997) and Hernandez et

al. (1996). Fluctuations of measured concentrations in a limited period can cause high

standard deviations. These high standard deviations generally indicate log-normal

distribution of the measured species. Besides the differences between the arithmetic mean

and geometric mean, there is a skewness in the concentration data, which give information

on the distribution of the data. Skewness values for all species were found to be more than

zero, which indicates right-tailed distribution, as expected. Standardized skewness (SS)

values of the species, except pH, were found to be more than +2 for all species, which

indicates a log-normal distribution. SS values of the species are depicted in Table 2.

3.4. Comparison of the species with the data from Mediterranean

Observed concentrations of the measured parameters were compared with the available

data from the Mediterranean area and a comparison is given in Table 3. The sulfate

concentration (115.2 Aeqv/l) was found to be very high when compared with those in the

literature for similar sampling sites on the Mediterranean except for the city of Antalya in

Turkey (113 Aeqv/l). The nitrate concentration (33.4 Aeqv/l) was also found to be one of

Table 3

Comparison of the major ion concentrations (Aeqv/l) in Bqyqkcekmece with other sites at the Mediterranean Sea

pH Cl� NO3� SO4

2� NH4+ Ca2+ K+ Mg2+ Na+

This study 4.81 124.8 33.4 115.2 12.8 285 57.4 99.6 75.2

Glavas and Moschonas (2002), Patras, Greece 5.16 114.3 19.4 46.1 16.3 98.5 6.6 30.4 90.2

Al-Momani et al. (1995), Antalya, Turkey 5.17 390 70 113 50 140 12.1 94 450

Avila and Alarcon (1999), Montseny, Spain 6.4 28.4 20.7 46.1 22.9 57.5 4.0 9.8 22.3

Plaisance et al. (1996), Morvan, France 5.25 14.7 18.8 29.4 57.0 12.4 6.4 13.3

Le Bolloch and Guerzoni (1995), Sardinia, Italy 5.18 322 29 90 25 70 17 77 252

Fig. 4. Seasonal variations in concentration of species in winter and summer.


the highest concentrations but less than Antalya city (7 Aeqv/l). These high sulfate and

nitrate concentrations produce low pH values. Accordingly, pH values observed in

Bqyqkcekmece were the lowest we measured. Average Ca2+ concentration in

Bqyqkcekmece is higher when compared to similar sites from Mediterranean. The

Mediterranean sites are considered to be under the influence of alkaline deposition linked

to desert dust outbreaks that moves Saharan dust towards Europe. Besides the Saharan

dust, soil content in Turkey has been recognized to be rich in Ca2+. Most probably these

two factors together increased the Ca2+ concentrations in the precipitation, which result in

high buffering capacity. The average K+ and Mg2+ concentrations of the samples collected

in Bqyqkcekmece were very high when compared with corresponding values. Na+ and

Cl� concentrations monitored in Bqyqkcekmece indicate intermediate values when

compared with these other sites. Furthermore, Cl/Na ratio calculation shows that Cl is

enriched in rainwater (Cl/Na=1.6) while this ratio in other sites is around 1.20. This

suggests that Na is not enriched and could be used for non-sea-salt calculations.

3.5. Seasonal variation of the species

The ratios of average concentrations of the species in summer to the corresponding

values in winter are depicted in Fig. 4. Most of the elements have higher concentrations in

the summer specially, concentrations of soil-derived species such as Ca2+, Al3+ and Fe3+.

These species are reduced during the winter because of increasing soil moisture.

Scavenging of pollutants from air by rainwater is an important process affecting

seasonality of the elemental concentrations. The monthly rainfall volume graph is given

Fig. 5. Monthly rainfall volume near Bqyqkcekemece Lake.


in Fig. 5, which shows that the study area is receiving high amount of precipitation

between June and December. Because there is more extensive scavenging in winter, the

higher concentrations of any species measured in winter indicates that they are emitted to

the atmosphere from sources close to the sampling site. For example, a typical marine

element, Cl�, has higher concentrations in winter than in summer. Sea salt particles are

coarse particles, which can settle quickly by gravitational action. Marine elements are

produced over the sea surface by the action of wind. Because the summer-to-winter ratio

of other marine elements, Na, K, and, Mg, are higher when compared to Cl�, it indicates

that Cl� has been enriched and it has other sources close to sampling site, beside sea.

3.6. Neutralization of the acidity

Although pH is a very common parameter which is used to judge if rainwater is acidic

or not, the pH unit alone gives very limited information on the acidity of rainwater.

Reactions taking place between the acidic and alkaline constituents and atmospheric water

determine the final pH of the rainwater. When SO2 and NOx gases or their oxidation

products of HNO3 and H2SO4 are dissolved in atmospheric water, they act as an H+ donor,

accordingly the pH of the rainwater decreases and acid precursors turn into NO3� and

SO42� anions. Knowledge of the concentrations of acidifying and neutralizing ions give

deeper information on the acidity of the rainwater. The high concentrations of the

neutralization element Ca2+ along with low pH values in the same rain event indicates that

the rainwater over Bqyqkcekmece Lake has a limited neutralization capacity. Ammonia

also is another neutralizing agent in rainwater. In our study the ammonia concentrations

measured were the lowest values among all the comparable sites on the Mediterranean

Sea. This indicates that ammonia does not have a significant role in pH neutralization in

rainwater over the sampling sites.

3.6.1. Correlation matrix

The correlation matrix is a useful technique to determine relations between the species

present in rainwater. In a correlation matrix the p-value is used as an indicator, which tests

the statistical significance of the estimated correlation. p-values below 0.05 indicate

statistically significant non-zero correlations at the 95% confidence level. Accordingly, the

correlation matrix has been constructed by using correlations only having p-values below

0.05. A correlation matrix of soluble deposition species in Bqyqkcekmece is depicted in

Table 4.

In most precipitation studies, the hydrogen ion is expected to have a strong correlation

with NO3�, and SO4

2�, which are known as major acidifying anions. In this study, there

are no significant correlations between H+ and such anions. When neutralizing species

are abundant in the rainwater, significant amounts of H+ ion are neutralized by these ions

and correlation between H+ and NO3� and SO4

2� can be masked by this neutralizing

effect.

Negative correlations between hydrogen ion and some soil-derived species in the table

is another factor supporting this idea. The greatest negative correlation was observed

between H+ and Ca2+, K+, Ba2+ and Mn2+. These ions could all be responsible for the

neutralization of rainwater to different extents.

Table 4

Correlation matrix of soluble deposition species in Bqyqkcekmece

H+ Cl� NO3� SO4

2� NH4+ Ca2+ K+ Mg2+ Na+ Al3+ Ba2+ Fe3+ Cu2+ Mn2+

H+ �0.53 �0.25 �0.36 0.35 �0.27

Cl� 0.26 0.60 0.63

NO3� 0.31 0.43 0.46 0.49 0.34 0.28 0.39 0.43 0.42

SO42� 0.72 0.40 0.44 0.53 0.57 0.76

NH4+ 0.36 0.44 0.32 0.25 0.23 0.58 0.24 0.41 0.35

Ca2+ 0.58 0.47 0.40 0.77 0.23 0.67

K+ 0.66 0.30 0.50 0.29 0.50

Mg2+ 0.56 0.36 0.45

Na+ 0.35 0.46

Al3+ 0.25 0.78 0.25

Ba2+ 0.41 0.58

Fe3+ 0.32

Cu2+ 0.41

Mn2+


SO42� and NO3

� have a strong correlation with each other as expected. Because these

ions, which are known to be primarily responsible for acid rain, are products of

combustion processes, mainly caused by industries, they are expected to have the same

sources.

Although both Ca and Al are known to be the most abundant crustal elements, no

significant correlation was observed between them. This could be due the fact that the data

used for correlation is for soluble fraction only not total concentration. While the soluble

fraction to insoluble fraction of Al in rainwater samples is close to zero, 20% of the Ca is

found to be dissolved. Because of that, correlation between Ca and Al may be obscured by

the different solubility of these species. Another explanation could be the direct influence

of the cement factory nearby Bqyqkcekmece Lake.

Significant correlations ( pb0.0001) are found between marine-derived species such as

Na+, Cl�, and Mg2+. Soil-derived species such as Ca2+, and Ba2+ are also correlated

( pb0.001). These results match with other workers results in the literature (Al-Momani et

al., 1997).

3.6.2. Enrichment factor

The enrichment factor (EF) gives information on the presence of non-crustal source

contributions to observed levels of elements in rainwater. The crustal enrichment factor

(EFc) of an element is calculated using the following relation.

EFc ¼�Cx=CAl

�RainSample�

Cx=CAl

�soil

where (Cx)RainSample is the concentration of the element in rainwater sample, while (Cx)soilis the concentration of the same element in the soil. CAl is the concentration of reference

element (Al) in the same sample and soil (Guerzoni et al., 1999; Nimmo and Fones, 1997).

Al, Ca, and Fe are typical lithophilic elements. Because soil is the only natural source

for lithophilic elements, and their composition in soil cannot be changed easily, one of


these elements can be used as a reference element. Al is commonly used as the reference

element in the literature, because it is the most abundant element in the earth crust.

Accordingly it is used as the reference element in this study. Chemical composition of the

soil is obtained from Mason’s Table (Mason, 1966). An EFc value close to unity indicates

the only source of that element to be soil. EFc values much higher than 1 indicates the

influence of sources other than the earth’s crust. Lithophilic elements do not appear to be

enriched in rainwater. This is not because of input from air borne soil but because of

scavenging of dust from the nearby cement factory. During cement clinker preparation, the

process requires four different calcium containing ores, two aluminum containing ores and

one iron containing ore.

Average enrichment factors for elements in Bqyqkcekmece rainwater are shown in Fig.

6. Total concentrations (soluble fraction+insoluble fraction of rainwater) of elements were

used in enrichment factor calculations.

Elements K, Fe, Mg, Na, Mn, Ca, and Ba have annual average EFc values less than

5. Among these Ca, Fe, and Ba are the elements for which the only known source in

the rural atmosphere is the earth crust. Consequently low EFc values for these elements

confirm their soil origin. Although these elements have EFc values less than 5, earth-

crust is not the only source for the remaining elements in the group. Some elements,

such as Na and Mg, are also produced over the sea surface and their low EFc values

indicate that these sources are masked by their significant abundance in the crustal

material. Cu is separated from other species with its tremendous EFc values (70),

which indicate that a very limited portion of Cu originated from earth-crust, although it

represents a good correlation with some of the earth-crust-originated species. Near by

the sampling site there are many industries, like a cement factory and copper

processing industrialized area. These could be the sources of high copper in the rain

samples.

3.7. Solubility of species

The solubility of each element is a complex process, which depends on the pH of the

rainwater as well as the type of particles. The solubility of different elements in rainwater

Fig. 6. Crustal enrichment factors (EFc) of rainwater species.

Table 5

Solubility of rainwater ions in Bqyqkcekmece

Soluble Insoluble Total % Solubility

Fe 0.01 11.20 11.21 0.06

Al 0.03 13.93 13.96 0.24

Ba 0.00 0.13 0.14 3.30

Mn 0.01 0.23 0.24 5.62

K 0.23 3.22 3.45 6.64

Mg 0.29 3.48 3.77 7.73

Cu 0.01 0.14 0.15 8.37

Ca 2.38 7.70 10.08 23.61

Na 1.40 1.18 2.57 54.35


is given in Table 5. The solubility was calculated by comparing the measured

concentrations of each specie in rainwater (filtrate or soluble part) and particles in rain

(residue on filter or insoluble part). One of the parameters that affects the solubility of

various species is the concentrations of these species. Some of the elements have a high

solubility at low concentration and as its concentration increases, the solubility decreases

(Alagha et al., 2002). Fe and Al has the lowest solubility (b1%) while Ca and Na has the

highest one (24.6 and 54.3, respectively). Furthermore, crustal elements have low

solubility in rainwater except Ca, which was found to be responsible for neutralization of

rainwater in different regions in Turkey (Al-Momani et al., 1997; Elagha et al., 2001). In

contrast, sea salt elements, e.g. Na and Cl, have the highest solubility where their sea salts

are totally soluble. Other marine elements like Mg and K have low solubility because they

are mainly coming from soil as they are not enriched as seen from Fig. 6.

4. Conclusion

This study was essential for establishing a data base about the air quality around one of

the most important watersheds for Istanbul city. The sampling sites were selected to

indicate the significance of aerial inputs of pollutants to the lake. The average pH of the

rain samples was 5.58 while the volume weighted average was found to be acidic with

typical values of 4.81. The Bqyqkcekmece area relies on coal and fuel oil for heating. A

natural gas supply network project for this region was ongoing during this study. Nearby

industrial areas mainly use fuel oil as a cheap energy source which adversely affects the air

quality in this region. Comparison of acid rain indicators, sulfates and nitrates, with other

workers shows that these pollutants are higher than other similar sites. Furthermore,

despite the high concentration of the neutralizing agent Ca2+, the pH levels were low

compared to other cities in the Mediterranean. Marine derived metals, like Na+ and Cl�

were found to be moderately higher than other sites because of the proximity of the

sampling site to the sea shore. Crustal elements, Ca2+, Al3+, Fe3+, show temporal variation

with higher concentrations during dry periods. SO42� and NO3

� show a significant

correlation ( pb0.005), which suggests that these pollutants are probably produced from

the same source, namely the high sulfur content fuels like coal and fuel oil used in

domestic heating and industry, respectively. Although the sampling sites are about 15 km


away from downtown, they are located between the main road and the highway. The

influence of nitrogen oxides from car emissions is still significant.

Acknowledgments

We would like to acknowledge Fatih University for the financial support of the project,

and also Prof. Gurdal Tucel and Prof. Semra G. Tuncel for allowing us to use their AAS

and ICP for analysis.

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The chemical composition of rainwater over Büyükçekmece Lake, Istanbul

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