3.1. PM2.5 Mass Concentration
The deposited mass concentration of the PM2.5 samples was calculated by weighting the polycarbonate filters before and after the sampling using a microbalance of six digits (Sartorius CC50). At the old Jeddah site, the total mass concentration of the PM2.5 samples varied from 12 to 85 µg/m3 with an annual average of 42.5 ± 13.3 µg/m3. The individuals and the annual mass concentration of the PM2.5 samples exceed the annual mass concentration proposed by the world health organization (WHO) which is equal to 10 µg/m3 (WHO, 2006). However, 80% of the individual mass concentration of the present PM2.5 samples exceeds the 24 hours mean value of the WHO and the annual mean values of the European commission of air quality (25 µg/m3) (EU, 2019). For comparisons, additional PM2.5 samples were assembled from another site (Alnaeem district) which illustrates a high mass concentration and it varies from 19 to 135 µg/m3 with an average of 61 ± 14.6 µg/m3. Figure 2 illustrates the monthly variation of the mass concentration of the PM2.5 samples collected from old Jeddah and Alnaeem districts. Remarkable high standard deviations were found at Alnaeem district especially during the autumn months. Also, the PM2.5 samples collected from the old Jeddah district during the spring have high standard deviations. At old Jeddah district, the highest mass concentration of the PM2.5 aerosols was found to be 54 ± 10 µg/m3 and 53 ± 3 µg/m3 during winter and spring seasons, respectively, Fig. 2. The high mass concentration of the PM2.5 aerosols in winter and spring could refer to the low wind speed and consequently the low atmospheric dispersion as well as the increase of the local burning activities.
The lowest mass concentrations of the PM2.5 samples were found during the months of the autumn (from September to November 2014), Figs. 2 and 3. The percentages of the individual mass concentration of the PM2.5 were depicted in Fig. 4. It was clear that about 95% of the collected PM2.5 samples from old Jeddah and Alnaeem districts is higher than the annual mean values of WHO, and 80% of them are also higher than the 24-hour values of WHO and the annual mean values of the European commission for air quality (EU, 2019; WHO, 2006). This illustrates that there is a remarkable challenge to decrease the mass concentration of the PM2.5 samples collected from old Jeddah and Alnaeem districts. However, only 10% of the total mass concentration of the PM2.5 samples collected from old Jeddah districts is higher than 60 µg/m3, Fig. 4. On the other hand, the old Jeddah district has a low mass concentration when comparing with the second location (Alnaeem). This could be due to the low density of the traffic inside the old Jeddah district as well as the decreasing of the number of inhabitants in the old Jeddah district whereas many residents prefer to move to the modern and new districts.
The high mass concentration of the PM2.5 samples at the Alnaeem district could refer to the high density of the traffic as well as the industrial activities around the sampling location. For comparisons of the present results with other published works in Jeddah, Table 1 presents the annual mean values of the PM2.5 found in the present work and the other published data in Jeddah. The present annual mean value of the PM2.5 mass concentration of old Jeddah is comparable with the previous work of Zytoon (Zytoon et al., 2014) and Aburas (Aburas et al., 2011). However, it seems to be higher than the values given by the others (Alghamdi, 2013; Khodeir et al., 2012; Lim et al., 2018). This present output result reflects the similarity and variability of the mass concentrations of the PM2.5 samples which depends on the nature of the sampling collection. Meanwhile, most of the published works regarding the atmospheric pollution in Jeddah city confirm that more than 70% of the total mass concentration of the PM2.5 samples is higher than the annual mean values of WHO and the European Commission of air quality. Therefore, there is an urgent need for scientific tools to decrease the mass concentration level of the PM2.5 aerosols in Jeddah.
Table 1
The average mass concentration of the PM2.5 samples reported in the present work and in the previous published works in Jeddah, Saudi Arabia.
Reference
|
City
|
Year
|
Mass concentration, µg/m3
|
Location Nature
|
Present Work
|
Jeddah
|
2014/2015
|
42.5 ± 6.4
60.7 ± 14.4
|
Residential (Old Jeddah)
Residential (Alnaeem)
|
WHO
|
10
|
Annual mean value
|
European Commission
|
25
|
Annual mean value
|
Aburas et al. (Aburas et al., 2011)
|
Jeddah
|
2008/2009
|
47.7 ± 16.5
67.8 ± 65.3
41.2 ± 4.8
47.3 ± 26.1
|
Residential
King Abdulaziz University
Residential/commercial
Residential
|
Alghamdi (Alghamdi, 2013)
|
Jeddah
|
2013
|
24.76 ± 8.71
13.13 ± 3.65
|
South of Jeddah
North of Jeddah
|
Khodeir et al. (Khodeir et al., 2012)
|
Jeddah
|
2011
|
15.8 ± 3.1
18.0 ± 4.0
73.2 ± 65.1
23.8 ± 11.7
29.1 ± 14.1
31.1 ± 5.8
24.5 ± 11.8
|
Residential
Residential
Suburban
Urban
Urban
Urban
Residential
|
Zytoon et al (Zytoon et al., 2014)
|
Jeddah
|
2008/2009
|
47.02 ± 19.15
41.15 ± 8.51
47.32 ± 25.37
67.77 ± 61.27
|
Residential
Residential/commercial
Residential
Industrial/commercial
|
Lim et al (Lim et al., 2018)
|
Jeddah
|
2011/2012
|
21.9 ± 11.6
|
Residential
|
3.2. Elemental Analysis of PM2.5 Samples
At three photon energy ranges, the XRF spectra of the PM2.5 samples were counted. For low Z elements, the excitation energy of the X-ray tube was carried out at a current of 15 mA and a voltage of 40 kV using a CaF2 secondary target. In this case, the low Z elements up to K (Z = 19) could be covered. Figure 5 illustrates an example of the XRF spectra of the low Z elements whereas the elements Al, Cl, K, Na, S, and Si can be identified. Besides, the excitation energy of the X-ray tube for the medium Z elements was executed using a germanium (Ge) secondary target at a maximum current and voltage of 8 mA and 75 kV, respectively. The medium Z element can be identified up to Zinc (Zn = 30), Fig. 6. Using a current of 7.5 mA, applied voltage of 80 kV, and Mo secondary target, the high Z elements could be quantified and these elements are Pb, Se, Br, Rb, Sr, and Y. One could recognize the L lines of W (Lα1 = 8.398 keV, Lα2 = 8.335 keV, Lβ1= 9.672 keV, and Lβ2= 8.398 keV) which originates mainly from the target of the X-ray tube, Fig. 7. According to the XRF spectra given by Figs. 5–7, twenty-two (22) elements were quantified in most of the PM2.5 samples and these elements are Al, Br, Ca, Cl, Co, Cu, Fe, K, Mn, Na, Ni, Pb, Rb, S, Sc, Si, Sr, Ta, Ti, V, Y, and Zn, Table 2 presents the minimum, maximum, and annual mean values for the elemental concentration in ng/m3 measured in the PM2.5 samples collected from old Jeddah and Alnaeem districts. The available air quality standard values of Pb and Ni were also presented in Table 2. Based on the elemental analyses of most elements illustrated in Table 2, the old Jeddah site has concentrations lower than the concentrations found at Alnaeem district. This indicates the low air pollution at the old Jeddah location in terms of elemental analysis. Also, the total mass concentration of the quantified elements represents 17.4% and 43% at old Jeddah and Alnaeem sites, respectively, Table 2. Therefore, the old Jeddah site has low concentrations of inorganic pollutants and high concentrations of volatile organic compounds (VOCs) in the PM2.5 samples. The situation is completely different in the Alnaeem district whereas the total mass concentration of the elements reaches 43%.
In the case of nickel (Ni), the average values observed in old Jeddah (25.8 ± 2.6 ng/m3) and Alnaeem (27.1 ± 3.4 ng/m3) districts are higher than the annual mean values of the air quality standards given by the European Commission (20 ng/m3). In addition, the individual quantitative analysis results of Ni in both locations are also higher than the value of the air quality standard. It was also recognized that there is remarkable stability of Ni in both sites during the whole year whereas the variations of the standard deviation values are within 10%. This indicates that the weathering conditions in the city have no influence on the increasing or decreasing the concentration of Ni in PM2.5 samples. The release of Ni and its compounds in the atmosphere was originated from industrial and commercial activities. As the nickel (Ni) level in the atmosphere is higher than the maximum allowance level, it could have toxicity, carcinogenicity, and pathological effects (Cempel & Nikel, 2006; Haber et al., 2000).
In the case of Pb, the daily concentrations in the old Jeddah district vary from 4 to 232 ng/m3 and all of these values are less than the annual mean values of the European Commission (500 ng/m3). At Alnaeem district, the daily concentration of Pb was also less than the annual mean values of the European commission except for one sample that has a concentration of 1177 ng/m3. However, the annual mean values of Pb at old Jeddah and Alnaeem districts are generally less than the annual mean values of air quality (500 ng/m3) and it equals 55 ± 70 and 371 ± 305 ng/m3, respectively.
The low concentration of Pb on both sides indicates the use of unleaded gasoline (Aburas et al., 2011). However, the high concentration of Pb at Alnaeem district could refer to the proximity of the different industrial activities including high traffic density. The low concentration of Pb in old Jeddah districts refers to the low traffic density since most of the trucks cannot pass inside the district.
Seven major elements were determined in the PM2.5 samples, namely Al, Ca, Cl, Fe, K, Na, and Si. These major elements are considered crustal elements and their origin from the sea spray and soil dust including dust storms and volcanic eruptions. It was recognized that the annual concentrations of these elements at Alnaeem district are always higher than their concentrations at the old Jeddah district. The concentrations of Si, K, and Fe at Alnaeem district are 4–6 times higher than that found at the old Jeddah location, Table 2. The high concentrations of Al, Ca, Fe, and Si at the Alnaeem district originate not only from the soil dust but also from the cement industries in the city. Jeddah has many locations specified from the cement industry where these elements represent the main ingredients. Therefore, the old Jeddah district has a low level of inorganic pollutants comparing with the new districts of the city whereas the average values of the total mass concentration of the PM2.5 in old Jeddah are always lower than that found at Alnaeem district. In the case of Na and Cl, the average concentration of Cl is always higher than the average concentration of Na and which is in agreement with the literature (Rossby & Egnér, 2016; Thimonier, Schmitt, Waldner, & Schleppi, 2008).
Table 2
The minimum, maximum and the mean values of the elemental analysis in the PM2.5 assembled from old Jeddah and Alnaeem districts.
El.
|
Old Jeddah District (S1), ng/m3
|
Alnaeem district (S2) ), ng/m3
|
Air Quality Standards
|
Min.
|
Max.
|
Mean
|
Min.
|
Max.
|
Mean
|
Na
|
65.1
|
1246.6
|
322.4 ± 292.8
|
121.9
|
916.9
|
394.0 ± 364.9
|
|
Al
|
18.3
|
4819.0
|
830.4 ± 980.6
|
692.7
|
7993.5
|
3249.4 ± 2909.7
|
|
Si
|
122.9
|
8424.6
|
1528.4 ± 1792.7
|
2177.6
|
15418.4
|
6597.8 ± 5256.3
|
|
S
|
50.3
|
4128.5
|
980.0 ± 1015.8
|
404.0
|
4669.3
|
2665.2 ± 1092.0
|
|
Cl
|
1.2
|
3584.4
|
832.0 ± 958.8
|
27.1
|
5256.5
|
1060.2 ± 1523.2
|
|
K
|
6.9
|
1599.1
|
316.8 ± 321.3
|
591.4
|
2690.0
|
1193.2 ± 737.9
|
|
Ca
|
46.2
|
6342.3
|
1777.3 ± 1598.8
|
1279.3
|
19787.1
|
7065.5 ± 5633.8
|
|
Sc
|
1.8
|
31.6
|
11.3 ± 9.2
|
6.4
|
6.4
|
6.4 ± 0
|
|
Ti
|
4.5
|
285.9
|
53.7 ± 61.3
|
102.4
|
755.5
|
289.5 ± 217.1
|
|
V
|
0.0
|
23.0
|
6.8 ± 6.0
|
0.9
|
23.1
|
12.9 ± 7.6
|
|
Mn
|
0.4
|
58.2
|
14.8 ± 15.3
|
22.6
|
197.6
|
82.4 ± 62.9
|
|
Fe
|
12.4
|
2880.8
|
577.7 ± 663.5
|
1167.3
|
8880.5
|
3554.0 ± 2687.9
|
|
Co
|
0.0
|
3.8
|
1.6 ± 1.1
|
0.0
|
6.0
|
2.6 ± 2.0
|
|
Ni
|
22.2
|
35.0
|
25.8 ± 2.6
|
21.3
|
33.5
|
27.1 ± 3.3
|
20
|
Cu
|
11.5
|
33.2
|
15.7 ± 4.2
|
15.9
|
46.5
|
25.3 ± 10.2
|
|
Zn
|
4.3
|
37.4
|
15.7 ± 12.3
|
3.6
|
107.2
|
28.0 ± 29.1
|
|
Br
|
1.6
|
12.1
|
6.1 ± 2.5
|
2.3
|
36.6
|
10.7 ± 10.2
|
|
Rb
|
0.1
|
6.2
|
1.7 ± 1.6
|
1.9
|
6.6
|
3.6 ± 1.4
|
|
Sr
|
0.1
|
31.5
|
7.1 ± 6.9
|
9.5
|
84.4
|
32.7 ± 23.9
|
|
Y
|
0.3
|
2.7
|
1.1 ± 0.7
|
0.7
|
1.2
|
0.9 ± 0.3
|
|
Ta
|
0.0
|
31.6
|
14.9 ± 7.4
|
8.1
|
19.2
|
13.6 ± 7.8
|
|
Pb
|
3.5
|
231.8
|
55.0 ± 69.9
|
14.8
|
1176.8
|
370.6 ± 304.7
|
500
|
Σ El.
|
|
|
7.40
|
|
|
26.74
|
|
PM2.5
|
|
|
42.49
|
|
|
60.74
|
|
%
|
|
|
17.41
|
|
|
43.93
|
|
The source of Cl on both sides is mainly from the sea spray and this could be expected whereas the annual concentrations of Cl and Na on both sides are comparable. Considering other natural and anthropogenic sources as well as the sea spray, the Na/Cl ratios could be varied from 0.5 to 1.5 (Thimonier et al., 2008). Figure 8 shows the obtained seasonal Na/Cl ratios of the present work. At the old Jeddah site, 30% of the Na/Cl ratios are within the range from 0.5 to 1.5 whereas 36% of the Na/Cl ratios of Alnaeem district are with the same range. The variation of the Na/Cl ratio far from the restricted range could be an indication of the existence of other sources rather than the sea spray. However, the seasonality of most of the Na/Cl ratios approaches the minimum restricted range, Fig. 8. The highest value of the Na/Cl ratios was found in winter whereas the Na/Cl ratios of the other seasons are comparable, Fig. 8.
Furthermore, the elements Mn, V, and Co originate from anthropogenic and natural sources. The expected anthropogenic sources have different contributions to these elements in the atmosphere such as traffic, power plants, coal, crude oil, iron ores, and steel industries (Moreno et al., 2011). Additional natural sources include the soil dust from wind erosion and suspensions of soils are also expected. The average values of Mn equal 14.8 ± 15.3 and 82.4 ± 63 ng/m3 at old Jeddah and Alnaeem locations, respectively. Mn increased 6 times at the Alnaeem site which indicates the traffic source. The annual mean value of Mn in old Jeddah is comparable with that found in Germany (Georgii & Muller, 1974). The average value of Mn found in the Alnaeem district is also comparable with that reported in Belgium (Kretzschmar, Delespaul, & de Rijck, 1980). The toxicity of Mn could depend on its oxidation states (Mn2+, Mn3+, and Mn4+) whereas the Mn2+ and Mn3+ oxidation states have a neurotoxic effect (Aschner & Aschner, 1991; Gavin, Gunter, & Gunter, 1990). Fortunately, a low concentration of Co was found at old Jeddah and Alnaeem locations (< 2.6 ng/m3) and it originates from the vehicular exhaust and the different industrial activities such as coal combustion and waste incineration. The high concentration of Co may cause health problems such as heart problems and Thyroid damage (Barceloux, 1999). The low concentration of Co at the old Jeddah site refers to the low traffic density. In the case of vanadium (V), it originates in the atmosphere mainly from anthropogenic sources such as petroleum refineries, steel industry, heterogeneous catalysts, and seagoing ships (Visschedijk, Denier van der Gon, Hulskotte, & Quass, 2013). However, V also could be emitted into the atmosphere from natural sources whereas its concentration in the earth’s crust reaches 100 µg g− 1 (Schaller, 1994). It was also observed that the concentration of V at the Alnaeem location is twice its value at the old Jeddah location.
In the case of Sulfur (S), the highest concentration was found at Alnaeem district and it reaches 4669 ng/m3. The mean concentration of S at the Alnaeem location is four times higher than that found at the old Jeddah site. As mentioned earlier, the old Jeddah site has low traffic density whereas the Alnaeem location has high traffic density and close to oil refinery activities. Although sulfur is mainly released in the atmosphere from various anthropogenic sources such as oil and coal combustion, petroleum refineries, and smelting of non-ferrous ores, it also releases in the atmosphere from other natural sources such as biogenic and non-biogenic sources (geothermal emission, volcanoes, and sea spray) (Andreae, 1986; Cullis & Hirschler, 1980). Looking at Cu and Zn, there is a remarkably low concentration of these elements on the old Jeddah site as illustrated in Table 2. The origins of Cu and Zn in the atmosphere could be the brass and alloy industries, vehicular emission, and galvanized metals.
Other minor elements were quantified on both sites and these elements are Sc, Ti, Br, Rb, Sr, Y, and Ta. The average concentration of these elements, except Ti and Sr, in both sites, is less than 15 ng/m3. The average mass concentrations of Br, Rb, Y, and Ta on both sides are comparable and the variations are among the standard deviations. The behavior of scandium (Sc) is completely different from all other elements whereas it has a higher concentration at the old Jeddah site. The scandium is rare in the earth’s crust and exists as a trace in different minerals. The natural origins of Ti and Sr seem to be dominating whereas they have the same behavior as the major elements like Ca and their highest concentrations were found at the Alnaeem site. Titanium (Ti) varies from 0.5 to 1.5% in the earth’s crust and it occurs in a form of different minerals such as brookite, anatase, ilmenite, and perovskite (Barksdale, 1966). However, Ti also releases into the atmosphere from the coal and oil combustion and titanium industry especially the production of TiO2 pigment.
3.3. Statistical Analysis
3.3.1. Enrichment Factor Calculations
Using the quantitative elemental analysis and the established information of the earth crust composition, the calculations of the enrichment factor could be explained the origins of the anthropogenic activities on the quality of the atmosphere. The quantified elements naturally exist in the earth’s crust and are crucial for humans, animals, and plants. The additional concentration of these elements could be released into the environment due to the different anthropogenic sources such as; industrial wastes, sewage sludge, and fertilizer impurities. As the concentration of these elements is equal to or less than its concentration in the earth’s crust, it gives a clear indication of the natural sources. On the other hand, if the concentration of these elements is higher than its concentration in the earth’s crust, it indicates anthropogenic origins. Therefore, the excess concentration of these elements in the earth’s crust usually causes adverse effects on humans, animals, and plants and might have a different degree of toxicity. For a reference crustal element Y and element X, the enrichment factor for the element X is given by,
Where (X/Y) is the concentration ratio of X and Y elements in the PM2.5 aerosols or the earth’s crust, respectively. Additional details about the enrichment factors could be found elsewhere (Barbieri, 2016; Bern, Walton-Day, & Naftz, 2019; Iqbal & Shah, 2015; Sukri et al., 2018). The reference crustal element (Y) is usually stable in the soil with natural origins and is used to normalizing its concentration in the PM2.5 aerosols. Aluminium (Al) has been selected as a reference element (Y) and it was previously considered as a conservative and low occurrence variability element (Ketterer, Lowry, Simon Jr, Humphries, & Novotnak, 2001; Schropp et al., 1990; Uduma, 2014; Yang et al., 2010). The chemical composition of the earth’s crust was provided by Wedepohl (Hans Wedepohl, 1995). Figure 9 depicts the relationship between the annual mean values of the EFs versus the quantified elements in the PM2.5 samples collected from the present two locations. If the values of the EFs equal to or less than 1, it indicates that the element of interest has a natural source from the earth’s crust. The elements Si, Al, and K originate from the natural source from the earth’s crust whereas the EFs values of these elements equal or less than 1. Also, there is no enrichment for Na and Rb found at the Alnaeem site which indicates the natural origins. Minimal enrichment could be observed as the values of the EFs are less than 2 (EFs < 2). The elements Fe, Ti, Rb, and Na quantified at the old Jeddah site have a natural origin with minimal enrichment values less than 2.
The moderate enrichment exists as the EFs range from 2 to 5 and this was found for Sr, Mn, and Y as illustrated in Fig. 9. The elements Sr, Mn, and Y have mainly natural origins such as seawater but it also releases into the atmosphere from other anthropogenic sources like coal combustion. A significant enrichment is expected when the EFs vary from 5 to 20. The main elements that have significant enrichment factors are Ca, V, and Co. A very high and extremely high enrichments could be expected when the EFs range from 20–40 and > 40, respectively. The enrichment factor of very and extremely high values (> 20) was found for the elements Cl, S, Zn, Cu, Ni, Sc, Pb, Br, and Ta. This illustrates that these elements originate from man-made sources. The high EF values of S, Cu, Zn, Ni, and Pb suggest the influence of traffic emissions, extensive mining, non-ferrous metal production, marine, fossil fuel combustion, and incinerator emissions (Aksu, 2015; Deboudt, Flament, & Bertho, 2004; Khodeir et al., 2012; Suvarapu & Baek, 2017).
3.3.2. Correlation Coefficients
As the elemental analysis of PM2.5 aerosols was carried out for different seasons, sites, and elements, the interrelationship of the quantified elements and the sampling seasons was explored by Pearson’s correlation coefficients. Therefore, the influence of the latent factors could be demonstrated. The calculations of Pearson’s correlation coefficients were carried out in terms of the variations of the quantified elements and the seasons of the year. The formula of the Pearson's correlation coefficients rxy is given by,
Whereexhibits the average value of i number of x's and expresses the average value of i number of y's. The correlation coefficient values (rxy) could be varying from − 1 to + 1. As the correlation coefficients approach + 1 or -1, it indicates the perfect positive or perfect negative correlations, respectively. There is no correlation between the variables when the coefficient values equal to zero (rxy= 0). As the correlation coefficient values vary from ± 0.5 to ± 1, it gives a strong positive or negative correlation.
Table 3
The correlation coefficients of Pearson between the quantified elements in the PM2.5 samples collected from old Jeddah site
|
Al
|
Si
|
S
|
K
|
Ca
|
Ti
|
V
|
Mn
|
Fe
|
Co
|
Ni
|
Cu
|
Zn
|
Pb
|
Br
|
Cl
|
Rb
|
Sr
|
Na
|
Al
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Si
|
1.00
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
S
|
0.85
|
0.83
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
K
|
0.97
|
0.96
|
0.89
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ca
|
0.81
|
0.83
|
0.58
|
0.72
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ti
|
0.98
|
0.99
|
0.84
|
0.96
|
0.81
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
V
|
0.60
|
0.59
|
0.79
|
0.62
|
0.54
|
0.58
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
Mn
|
0.82
|
0.84
|
0.72
|
0.76
|
0.86
|
0.83
|
0.61
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
Fe
|
0.97
|
0.99
|
0.84
|
0.95
|
0.79
|
1.00
|
0.58
|
0.83
|
1.00
|
|
|
|
|
|
|
|
|
|
|
Co
|
0.42
|
0.41
|
0.39
|
0.45
|
0.19
|
0.40
|
0.35
|
0.25
|
0.37
|
1.00
|
|
|
|
|
|
|
|
|
|
Ni
|
0.87
|
0.87
|
0.80
|
0.88
|
0.72
|
0.87
|
0.63
|
0.73
|
0.86
|
0.38
|
1.00
|
|
|
|
|
|
|
|
|
Cu
|
0.91
|
0.91
|
0.80
|
0.89
|
0.77
|
0.92
|
0.60
|
0.76
|
0.90
|
0.48
|
0.83
|
1.00
|
|
|
|
|
|
|
|
Zn
|
0.46
|
0.44
|
0.30
|
0.37
|
0.38
|
0.42
|
0.27
|
0.45
|
0.37
|
0.37
|
0.31
|
0.50
|
1.00
|
|
|
|
|
|
|
Pb
|
0.43
|
0.44
|
0.61
|
0.47
|
0.29
|
0.47
|
0.42
|
0.46
|
0.50
|
0.14
|
0.42
|
0.45
|
-0.12
|
1.00
|
|
|
|
|
|
Br
|
0.07
|
-0.01
|
0.12
|
0.15
|
-0.20
|
0.01
|
0.08
|
-0.14
|
-0.04
|
0.37
|
0.13
|
0.12
|
0.23
|
-0.25
|
1.00
|
|
|
|
|
Cl
|
0.20
|
0.12
|
0.08
|
0.25
|
-0.03
|
0.14
|
-0.15
|
0.01
|
0.10
|
0.28
|
0.11
|
0.18
|
0.24
|
-0.09
|
0.63
|
1.00
|
|
|
|
Rb
|
0.71
|
0.71
|
0.44
|
0.67
|
0.71
|
0.74
|
0.28
|
0.63
|
0.73
|
0.21
|
0.64
|
0.68
|
0.25
|
0.15
|
0.07
|
0.21
|
1.00
|
|
|
Sr
|
0.94
|
0.96
|
0.82
|
0.92
|
0.80
|
0.95
|
0.58
|
0.80
|
0.95
|
0.41
|
0.84
|
0.92
|
0.35
|
0.48
|
0.05
|
0.20
|
0.74
|
1.00
|
|
Na
|
0.58
|
0.52
|
0.49
|
0.61
|
0.29
|
0.51
|
0.27
|
0.34
|
0.47
|
0.50
|
0.44
|
0.56
|
0.54
|
0.08
|
0.60
|
0.81
|
0.40
|
0.52
|
1.00
|
Table 4
The correlation coefficients of Pearson between the quantified elements in the PM2.5 samples assembled from Alnaeem site
|
Al
|
Si
|
S
|
K
|
Ca
|
Ti
|
V
|
Mn
|
Fe
|
Co
|
Ni
|
Cu
|
Zn
|
Pb
|
Br
|
Cl
|
Rb
|
Sr
|
Na
|
Al
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Si
|
0.99
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
S
|
0.25
|
0.20
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
K
|
0.94
|
0.97
|
0.15
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ca
|
0.70
|
0.76
|
0.01
|
0.88
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Ti
|
0.88
|
0.92
|
0.08
|
0.98
|
0.94
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
V
|
0.51
|
0.48
|
0.87
|
0.48
|
0.36
|
0.42
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
|
Mn
|
0.89
|
0.93
|
0.06
|
0.97
|
0.91
|
0.99
|
0.40
|
1.00
|
|
|
|
|
|
|
|
|
|
|
|
Fe
|
0.88
|
0.92
|
0.06
|
0.97
|
0.93
|
1.00
|
0.41
|
1.00
|
1.00
|
|
|
|
|
|
|
|
|
|
|
Co
|
-0.03
|
0.02
|
-0.04
|
0.01
|
0.17
|
0.05
|
-0.15
|
0.11
|
0.08
|
1.00
|
|
|
|
|
|
|
|
|
|
Ni
|
0.74
|
0.75
|
0.50
|
0.81
|
0.75
|
0.79
|
0.67
|
0.77
|
0.79
|
0.13
|
1.00
|
|
|
|
|
|
|
|
|
Cu
|
0.76
|
0.80
|
0.19
|
0.86
|
0.84
|
0.87
|
0.58
|
0.88
|
0.88
|
0.01
|
0.80
|
1.00
|
|
|
|
|
|
|
|
Zn
|
0.62
|
0.64
|
0.25
|
0.75
|
0.76
|
0.79
|
0.49
|
0.72
|
0.75
|
-0.18
|
0.68
|
0.77
|
1.00
|
|
|
|
|
|
|
Pb
|
0.08
|
0.08
|
-0.01
|
-0.02
|
-0.08
|
-0.01
|
-0.08
|
-0.01
|
-0.02
|
-0.15
|
-0.05
|
-0.01
|
0.04
|
1.00
|
|
|
|
|
|
Br
|
0.66
|
0.70
|
0.06
|
0.75
|
0.73
|
0.77
|
0.47
|
0.82
|
0.81
|
-0.01
|
0.63
|
0.86
|
0.49
|
-0.29
|
1.00
|
|
|
|
|
Cl
|
0.48
|
0.51
|
-0.05
|
0.65
|
0.83
|
0.73
|
0.22
|
0.63
|
0.69
|
-0.10
|
0.56
|
0.61
|
0.79
|
0.08
|
0.36
|
1.00
|
|
|
|
Rb
|
0.50
|
0.54
|
0.09
|
0.71
|
0.86
|
0.74
|
0.42
|
0.67
|
0.72
|
0.00
|
0.76
|
0.72
|
0.67
|
-0.30
|
0.61
|
0.82
|
1.00
|
|
|
Sr
|
0.72
|
0.78
|
0.04
|
0.89
|
0.99
|
0.95
|
0.40
|
0.93
|
0.95
|
0.13
|
0.76
|
0.86
|
0.75
|
-0.10
|
0.79
|
0.79
|
0.84
|
1.00
|
|
Na
|
0.39
|
0.39
|
0.43
|
0.45
|
0.43
|
0.45
|
0.41
|
0.34
|
0.38
|
-0.15
|
0.48
|
0.30
|
0.75
|
0.33
|
-0.09
|
0.63
|
0.39
|
0.40
|
1.00
|
A moderate negative or positive correlation could be obtained when the correlation coefficient values vary from ± 0.3 to ± 0.49. The low degree of correlation could be expected as the correlation coefficient values less than ± 0.3 ( < ± 0.3). Tables 3 and 4 illustrate the correlation coefficient values between the different quantified elements at the current two locations.
Sodium (Na) on both locations has low and/or moderate correlations with most of the quantified elements except Cl, whereas there is a strong correlation between Na and Cl in both locations which indicates the sea spray sources. Low negative and positive correlations were found between Co and other elements in most of the quantified elements at the two sites. Perfect and strong positive correlations ranging from 1 to 0.70 were found for most of the crustal elements namely; Al, Ca, Fe, K, Mn, Si, and Ti. The correlation of sulfur (S) with other elements at the two sampling locations is completely different. In the old Jeddah district, S has strong correlations with most crustal elements and anthropogenic elements namely; Ca, Cu, Fe, K, Mn, Na, Ni, Sr, Ti, Pb, and V. The strong correlation of S with the anthropogenic elements such as Cu, Ni, and Pb could be originated from the different mobile and stationary sources like trucks, cars, and power plants. However, S has only strong correlations with V, Ni, Ta, and Na at Alnaeem district, and these elements are mostly produced from oil combustion and sea spray. Therefore, it seems that S in the current two sites has different anthropogenic origins rather than oil combustion at each site. The same behavior was found for Pb whereas it has moderate correlations with all elements except S whereas there is a strong correlation between Pb and S at old Jeddah. At the Alnaeem location, Pb has low correlations with all elements without exception. Therefore, Pb has also different origins at both locations and stays in the atmosphere for a long time. These sources are the industrial processes, coal and oil combustion, and leaded gasoline. The correlation coefficients of the seasons of the year illustrate a strong correlation between the different seasons, Table 5. However, the lowest correlation was found between the winter and summer seasons whereas the winter season is characterized by high energy consumption, high vehicle emission, and low dispersion of the mass concentration of the PM2.5aerosols.
Table 5
The correlation coefficients of Pearson between the seasons of the year in the PM2.5 samples from old Jeddah site
Seasons
|
Autumn 2014
|
Winter 2014/15
|
Spring 2015
|
Summer 2015
|
Autumn 2014
|
1.00
|
|
|
|
Winter 2014/15
|
0.96
|
1.00
|
|
|
Spring 2015
|
0.97
|
0.88
|
1.00
|
|
Summer 2015
|
0.89
|
0.75
|
0.89
|
1.00
|
3.3.3. Source Identification using Principal Component Analysis (PCA)
The source identification could be explored from the relation between the quantified elements in the PM2.5 aerosols. The principal component analysis (PCA) was applied to reduce the number of variables (the quantified elements) into a few components that explain the origins and the relationship among the quantified elements. The principal components are the eigenvectors of the data’s covariance matrix. Figure 10 illustrates the relationship between the total variance (%) versus the principal components for the quantitative elemental analysis of the PM2.5 assembled from the old Jeddah and Alnaeem sites. For the separation of the component, the total variance of the analysis is based on Varimax rotation and Kaiser Normalization. Table 6 shows the contribution of each element in the component matrix. At the old Jeddah site, five components explain 84% of the total variance of the analysis. The first component represents ~ 53% of the total variation and it refers to the natural sources of the earth’s crust elements. Most of the quantified elements contribute to the natural origins except Ta, Br, Cl, Y, and Sc. Also, the elements Co, Zn, Pb, and Na have mixed natural and anthropogenic origins whereas they have a moderate contribution to the first component. The second component represents 12% of the variation and it represents the sea spray sources whereas Na, Br, and Cl are the main contributors, Table 6. The third component represents ~ 8% of the variation and it could be originated from traffic-related air pollution such as the combustion of heavy fuel oils and vehicle exhausts. A moderate and low contribution of the elements S, K, V, Co, Ni, Pb, and Br represent the main source, Table 6. The elements S, Co, Ni, and Pb could be released into the atmosphere from the traffic with diesel-fuelled vehicles. The fourth and fifth components represent 7% and 5%, respectively. They represent the mixed origins between the natural, anthropogenic, and sea spray sources.
For comparison, four components represent 93% of the total variance of the analysis at Alnaeem district, Fig. 10, and Table 7. The first component approximately equals 64% of the total variation and it indicates the natural sources of the earth’s crust elements. Although the elements S, V, Ta, Br, Cl, Y, and Na have anthropogenic and sea spray sources but they have a moderate contribution to the natural sources at the first component. Other anthropogenic elements have no contribution to the first component namely; Co, Pb, and Y. The second component represents ~ 15% of the variation and it originates mainly from anthropogenic sources including, alloy smelters, vehicle exhausts, and oil and coal combustions. The main contributed elements for the second components are S, V, Co, Ni, Zn, Ta, and Pb, Table 7. The third component represents ~ 9% and originates from other anthropogenic sources such as mining activities, power plants, metal production, mineral production, manufacturing industries, and construction. The main contributed elements for the third component are Al, Si, S, V, Mn, Fe, Co, Cu, and Br. The fourth component represents 5% and it could refer to the sea spray, power plants, and the released smoke from automobile exhausts. The contributed elements for the fourth component are Al, Ca, V, Co, Cu, Zn, Br, and Cl.
Table 6. Five component matrix for the quantified elements in PM2.5collected from old Jeddah site.
|
Component Matrix
|
1
|
2
|
3
|
4
|
5
|
Al
|
.983
|
.009
|
-.040
|
.041
|
.002
|
Si
|
.972
|
-.068
|
-.063
|
-.004
|
-.002
|
S
|
.878
|
-.114
|
.326
|
.086
|
-.099
|
K
|
.965
|
.029
|
.135
|
.128
|
.008
|
Ca
|
.820
|
-.210
|
-.397
|
-.061
|
.074
|
Ti
|
.980
|
-.074
|
-.046
|
.050
|
.037
|
V
|
.669
|
-.207
|
.300
|
-.083
|
.093
|
Mn
|
.856
|
-.197
|
-.236
|
-.019
|
-.090
|
Fe
|
.968
|
-.128
|
-.035
|
.057
|
.028
|
Co
|
.448
|
.404
|
.313
|
-.478
|
-.125
|
Ni
|
.887
|
-.060
|
.064
|
.105
|
.133
|
Cu
|
.944
|
.045
|
-.006
|
-.088
|
.030
|
Zn
|
.453
|
.451
|
-.334
|
-.395
|
-.147
|
Ta
|
-.216
|
-.116
|
.191
|
.753
|
.383
|
Pb
|
.482
|
-.430
|
.282
|
.157
|
-.435
|
Br
|
.091
|
.801
|
.337
|
.148
|
.194
|
Cl
|
.191
|
.838
|
.003
|
.341
|
-.122
|
Rb
|
.718
|
.040
|
-.339
|
.124
|
.384
|
Sr
|
.960
|
-.045
|
-.014
|
.057
|
.018
|
Y
|
.082
|
-.012
|
.367
|
-.602
|
.588
|
Na
|
.584
|
.734
|
.049
|
.139
|
-.131
|
Sc
|
.154
|
-.214
|
.780
|
-.018
|
-.127
|
Table 7. Four component matrix for the quantified elements in PM2.5 collected from Alnaeem district.
|
Component Matrix
|
1
|
2
|
3
|
4
|
Al
|
.885
|
− .045
|
.226
|
− .294
|
Si
|
.903
|
− .070
|
.211
|
− .287
|
S
|
.551
|
.653
|
.468
|
.139
|
K
|
.962
|
− .124
|
.070
|
− .134
|
Ca
|
.932
|
− .245
|
− .165
|
.067
|
Ti
|
.966
|
− .179
|
− .027
|
− .101
|
V
|
.754
|
.294
|
.387
|
.149
|
Mn
|
.938
|
− .229
|
.099
|
− .159
|
Fe
|
.955
|
− .227
|
.031
|
− .123
|
Co
|
− .372
|
.118
|
.698
|
.334
|
Ni
|
.924
|
.019
|
.096
|
− .023
|
Cu
|
.910
|
− .144
|
.186
|
.083
|
Zn
|
.862
|
.235
|
− .197
|
.349
|
Ta
|
.709
|
.689
|
.006
|
.003
|
Pb
|
− .045
|
.640
|
− .255
|
− .610
|
Br
|
.725
|
− .522
|
.294
|
− .034
|
Cl
|
.730
|
− .044
|
− .597
|
.223
|
Rb
|
.812
|
− .310
|
− .303
|
.281
|
Sr
|
.937
|
− .266
|
− .115
|
.036
|
Y
|
− .717
|
− .681
|
.008
|
− .011
|
Na
|
.580
|
.677
|
− .362
|
.163
|