Jordan Journal of Chemistry Vol. 7 No.3, 2012, pp. 311-328
311
JJC
Identification of Polycyclic Aromatic Hydrocarbons in Air Samples from Zarqa City, Jordan, Using High Resolution Laser Excited Luminescence Spectroscopy Combined with Shpolskii Matrix
Technique
Yaser A. Yousef∗, Ahmed A. Alomary, Abdulrahman Shwayat, Idrees F. Almomani
Chemistry Department, Faculty of Science, Yarmouk Univesity, Irbid, Jordan Received on June 6, 2012 Accepted on July 12, 2012
Abstract Laser excited luminescence combined with Shpolskii matrix techniques were used for the
detection and identification of PAH pollutants in the atmosphere of the northern part of Zarqa city
in Jordan. The weather conditions in that area are dry and dusty most of the year. The presence
of the oil refinery plant and the thermal power station in addition to most of the local industries
are considered as the major sources of pollution to the atmosphere of that area. The extent of
pollution was detected by measuring the concentration levels of Polycyclic Aromatic
Hydrocarbons (PAHs). Air samples from the airborne of Zarqa were collected at different time
intervals using high volume air sampler. A clean-up procedure, soxhlet extraction, was used
before subjecting samples to analysis. Gas Chromatography (GC) was used for quantitative
analysis of sample components. Cooling the samples down to 77K was sufficient to produce an
environment similar to Shpolskii matrix which is necessary for resolving the complex
fluorescence spectra of PAH compounds. PAHs of low molecular weights such as fluorine,
phenanthrene, chrysene, and the most dangerous carcinogen namely benz(a)pyrene, were
dominant in all samples. The total average of PAHs concentration varied from (7.3 ng/m3) for
benz(a)pyrene to (48.3 ng/m3) for phenanthrene.
Keywords: Benz(a)pyrene; GC; Laser Excited Luminescence (LEL); PAHs; Zarqa.
Introduction Air pollution has long been a severe problem facing human beings. From
several air pollutants, it is of particular interest to concentrate on the most dangerous
group, namely polycyclic aromatic hydrocarbons (PAHs)[1,2,3]. They are sometimes
referred to as polynuclear aromatic hydrocarbons or as polycyclic aromatic
compounds. Aromatics (including PAHs) are considered to be the most acutely toxic
component of petroleum products, and are also associated with chronic and
carcinogenic effects [4]. Most of PAHs with low vapor pressure in air are adsorbed on to
the surface of the dust particles. Therefore, they are believed to be major contributors
to the higher death rate from lung cancer in urban areas as compared to rural
areas[5,6].
∗ Corresponding author: e-mail: [email protected]
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Zarqa, the second largest city in Jordan and home of 52% of the industries in
the country, suffers the worst water shortage and air pollution. Zarqa's climate is
desert-like, to a much greater degree than nearby Amman. The major air pollution
sources in the city are the national refinery complex and Hussein thermal power
station. The determination of the levels of PAHs in the air of that area is of great
importance for the whole country.
One of the most sensitive techniques used for detecting PAHs is the Laser
Excited Fluorescence (LEF) which can reach limits of detection several orders of
magnitude higher than Gas Chromatography (GC) and High Performance Liquid
Chromatography (HPLC) [7,8]. Recent advances in LEF have shown the possibility of
single molecule detection [9,10,11]. Combining LEF with Shpolskii matrix individual PAH
compounds can be identified without the need of using classical chromatographic
separation techniques [12,13]. Cooling the samples in a proper solvent highly enhances
the fluorescence intensity and significantly reduces the width of the fluorescence
bands. Cryogenic temperatures close to 10 K is one of the necessary conditions to
produce fluorescence lines characteristic to Shpolskii matrix. Solvent chain length,
concentration and excitation line width are the other necessary conditions. It was
believed that only at this range of temperature, the width of the fluorescence lines
becomes sharp enough to be used for the identification of PAH compounds. In this
work, similar resolution could be achieved by cooling the samples to 77K using liquid
nitrogen. The success in sample analysis at this temperature is expected to make the
technique more popular due to the low cost in using liquid nitrogen as compared to the
cost and difficulty in using liquid helium. It is hoped that this result will encourage
further use of the technique for environmental analysis of PAH pollutants.
Experimental Samples collection
The sampling site, selected to characterize the PAH concentrations in the
ambient air, was located in Alhashemite industrial centre 2km from the refinery
complex. The sampling of the suspended particulate matter (SPM) was carried out
using a high volume sampler (TE-5170D-BL-INT, Packwill Environmental, Canada).
The sampler was kept at the rooftop of the municipal building about 13m above the
ground. The airborne particles were collected for 6 hour time periods on glass-fibbers
filter papers (size: 8” ×10”). A standard clean up, extraction, and volume reduction
procedure were followed, as described by Wenclawiak et al.[13]. A total of thirty samples
were collected from the sampling site during the period July to December 2004.
Chemicals
Solid standards, (anthracene and pyrene), were purchased from Aldrich,
Germany, and used as received. Standard solution containing 13 PAHs (EPA 525 PAH
mix A) in methylene chloride where purchased from Subelco, USA. Details of the
standard composition are given in table 5. Spectroscopic grade n-heptane and hexane
313
were purchased from Synchemica USA, and used as received. HPLC grade
dichloromethane was purchased from Aldrich. No detectable emission signals were
observed from all above solvents when excited in the range (250-500 nm). Silica and
alumina, (60 mm particle size), were purchased from Fluka. Liquid nitrogen was
obtained from the physics department.
Laser Excited Fluorescence (LEF) Set-up:
A block diagram for the LEF set-up is shown in figure 1. It is a modified version
of a home assembled system described in a previous work [14]. Nitrogen laser, PRA
(model LN-1000) (337.1 nm and 1mJ pulse energy) was used as the excitation light
source. The sample cell holder was a home designed and fabricated unit. It consists of
a pressure sealed stainless steel semi- spherical block with a quartz window. The cell
is designed for front surface excitation and emission. The topside of the cell can be
fitted to the tip of a homemade open cycle liquid nitrogen cryostat described in a
previous work [15]. Cell temperature was monitored by measuring the bias voltage
across a silicon diode fixed to the base of the cell. Chromex spectrograph (model
5001) with variable resolution is used to analyze the sample emission. It contains a set
of 3 gratings (75,150,300 grooves/mm) mounted on a turret. CCD, Princeton
Instruments (model ICCD-512x376) was used for detection. A programmable high
voltage pulsar (Princeton, model PG-200) is used to control the exposure time of the
CCD. Data acquisition, timing, and detector temperature were controlled by Model ST-
138 detector controller. Delay generator, Stanford Research Systems (model DG-535),
was used to synchronize the trigger of the high voltage pulsar with the laser and the
electromechanical shutters. Winspec software operating under Windows workgroups
V.3.11 was used to control the operation of the whole system and for data acquisition.
Gas Chromatography
GC Model-1000 from DANI Instruments was used for the separation and
quantitative analysis of the PAH compounds. The operating parameters for the unit are
listed in table 1.
Table 1: GC operating conditions
INSTRUMENT DANI GC 1000 INJECTOR Split-less mode. 250oC Detector Flame Ionization Detector (FID), 350 oC Column Capillary, 10m length x 0.53 mm id x- 2.65 µm film thickness,
Dimethyl-polysiloxane. Carrier Carrier: N2, flow 4 ml/min Oven 70 to 220 °C, rate 10 °C/min, hold time 20 min. Sample volume 5 µl
314
LN-1000N2 Lasr 1 2
3
45
6 78
Spectrograph
Cryostat
ICCD (OMA IV)
ST- 138Detector controller
Comm 2Serial port
9 10
11
12 13
14
15
8 8 8
Temperature Indicator
PG - 200Fast Pulser
DG- 535Delay Generator
Oil vacuum pump
Oilless pumpLiquid nitrogen dewer
Figure 1: Low temperature fluorescence setup, (1,2 -quartz window, 3 – sample cell, 4,5,6,7 mirrors, 8-grating, 9,10 laser input output, 11 electromechanical shutter, 12,13,14 controller I/O, 15 pulsar I/O). Results and Discussion
The room temperature fluorescence spectrum for a solution of pyrene in n-
heptane is shown in figure 2.a. The spectrum is known to have a broad fluorescence
band which cannot be used for the identification of the compound in a mixture of PAHs
sample [12]. Figure 2-b shows the low temperature fluorescence spectrum of the same
sample of pyrene in n-heptane at 77 K. It is clear that it consists of highly resolved
narrow spectral lines that can be easily used as fingerprint for the molecule in high
resolution mode of analysis. The spectrum obtained here has a comparable or better
resolution than the spectrum reported by Abu-Zeid et al., although the latter was
recorded at 15K temperature [12]. This can be attributed to experimental conditions
such as the alignment optics, laser energy, and the sensitivity of the Charge Coupled
Device (CCD). The room and low temperature spectra for a number of standard
compounds such as pyrene, anthracene ..etc were recorded and stored as standard
spectra for comparison purposes. The collected spectra were in good agreement with
315
those reported in the spectral atlas of organic compounds [16]. Further more, the
spectrum for a standard mixture sample containing 13 PAHs, (Subelco, EPA 525
PAHs mix A), was recorded at both room and low temperatures. The complete low
temperature spectrum was divided into four spectral frames, each of 20 nm width.
Figure 3 contains four spectral frames each shows the presence of a number of
compounds. Figure 3-a shows 9 sharp peaks related to the presence of anthracene,
benzo(a)anthracence, pyrene, and dibenzo(a,h)anthracence in the sample matrix. The
other three spectral frames are shown in their corresponding frames while the numbers
indicated above the peaks are related to the expected compounds. The spectral
frames in figure 3 could be successfully used to identify the compounds that were
detected with high sensitivity from the real samples.
Figure 2.a: Emission spectrum of pyrene solution at room temperature using low
resolution grating (150 groves/mm).
0.E+00
2.E+04
4.E+04
6.E+04
8.E+04
1.E+05
1.E+05
1.E+05
350 370 390 410 430 450 470 490
rela
tive
inte
nsity
wavelength (nm)
316
Figure 2.b: Low resolution emission spectrum for the same sample in figure (2-a)
obtained at the same conditions except for the sample temperature 77K.
For demonstration purposes, the spectrum of one of the first period samples is
shown in figure 4. The results indicate the capability of the technique for the
identification of PAHs in the atmosphere. In addition, the technique has a low detection
limit; it was possible to detect all compounds in a standard mixture containing 50ng/ml
for each. Furthermore, the results indicate the presence of some PAHs in the study
area in concentrations close or higher to the concentration of the standard sample.
However, due to several experimental parameters such as variations in laser pulse to
pulse intensity, optical alignment, and internal or self absorption, the technique is
generally used for identification and semi-quantification analysis [17].
0.E+00
2.E+04
4.E+04
6.E+04
8.E+04
350 400 450 500
rela
tive
inte
nsity
wavelength (nm)
317
Figure 3.a: High resolution emission spectrum for a mixture of PAH's (0.5 ppm each)
obtained at 77K, numbers indicate the characteristic peaks for the following
compounds; 1 and 2 for anthracene; 4 and 5 for benzo(a)anthracene; 3, 6, 7 and 8 for
pyrene and 9 for dibenz(a,h)anthracene.
2.E+05
2.E+05
2.E+05
3.E+05
375 380 385 390 395
rela
tive
inte
nsity
wavelength (nm)
12
3
5
6
7
8
4
9
318
Figure 3.b: Emission spectrum for a mixture of PAHs (0.5 ppm each) obtained at 77K,
numbers indicate the characteristics peaks for the following compounds; 1, 7 for
benzo(a) pyrene. 2, 3,4,10 for benzo(g,h,i) perylene, 6,8, 9 for benzo(b)fluoranthene.
1
23
4 5
6
7
89
10
11
319
Figure 3.c: Third frame of emission spectrum for a mixture of PAHs (0.5 ppm each) obtained at 77K. Number (1) indicate the characteristic peak for phenanthrene molecule.
Figure 3.d: Last frame of emission spectrum for a mixture of PAHs (0.5 ppm each) obtained at 77K. All peaks are related to chrysene molecule.
6.E+04
7.E+04
8.E+04
9.E+04
1.E+05
1.E+05
458 460 462 464 466 468 470
Rel
ativ
e In
tens
ity
Wavelength (nm)
1
3.E+04
6.E+04
9.E+04
1.E+05
2.E+05
2.E+05
2.E+05
495 500 505 510 515 520
Rel
ativ
e in
tens
ity
Wavelength (nm)
320
Quantitative analysis is usually carried out using GC technique combined with
the method of internal standard. For this purpose, the collected samples were
analyzed for PAH components by GC. A 10 meter capillary column was used to
resolve the complex sample matrix. Figure 5 shows a GC chromatogram obtained for
the standard sample mixture containing 13 PAHs (EPA 525 PAH mix A). The retention
times and the peak areas for the eluted compounds are shown in table 2 and given in
figure 5.
Table 2: Retention times and peak areas for compounds recorded in figure 5.
No. Name Retention Time (min)
Peak Area
1 Acenaphthylene 7.78 380
2 Fluorine 8.80 277
3 Phenanthrene 9.95 911
4 Anthracene 10.4 1245
5 Pyrene 13.4 583.7
6 Benzo (a) anthracene 14.6 1753
7 Chrysene 15.7 1687
8 Benzo (b) fluoranthene 16.4 2128
9 Benzo (k) fluoranthene 19.1 871
10 Benzo (a) pyrene 21.9 3106
11 Indeno (1, 2, 3-cd) pyrene 22.3 1840
12 Dibenzo (a, h) anthracene 23.8 581
13 Benzo (ghi) perylene 24.2 620
321
Figure 4.a: First Frame of emission spectrum for an air polluted sample sample at 77K
using high resolution grating, numbers indicate the characteristics peaks for the
following compounds; 1, 2, 3, 4 for pyrene, 5 for dibenz(ah)anthracene.
1.E+05
1.E+05
1.E+05
2.E+05
2.E+05
2.E+05
2.E+05
2.E+05
3.E+05
380 385 390 395 400
Rel
ativ
e in
tens
ity
Wavelength (nm)
1
2
3
4
5
322
Figure 4.b: Second frame of emission spectrum for same sample in (4-a) at 77K using
high resolution grating at 77K, numbers indicate the characteristics peaks for the
following compounds; 1, 3 and 5 for benzo(a)pyrene; 4, 6, 7 and 8 for
benzo(b)fluoranthene; 2 and 9 for Benzo (g, h, i) Perylene.
1.E+05
1.E+05
1.E+05
2.E+05
2.E+05
2.E+05
2.E+05
2.E+05
2.E+05
2.E+05
2.E+05
400 405 410 415 420
rela
tive
inte
nsity
Wavelength (nm)
1
2
3
4
56
7
8
9
323
Figure 4.c: Third frame of emission spectrum at 77K. Peaks are assigned for
phenanthrene.
430.00 440.00 450.00 460.00 470.00Wavlength (nm)
4.0E+4
8.0E+4
1.2E+5
1.6E+5
2.0E+5
Rel
ativ
e In
tens
ity
1
2
3
Wavelength (nm)
324
Figure 4.d: Last frame of emission spectrum at 77K.
Figure 5: GC chromatogram for 13 PAHs Standard, 1ppm each. Names retention times correspond to each peak number are summarized in table 2.
1.E+05
2.E+05
2.E+05
3.E+05
3.E+05
4.E+05
480 490 500 510 520
rela
tive
inte
nsity
Wavelength (nm)
10
40
70
100
130
5 10 15 20 25
mv
Retention time (min)
12
34
5
6 78
9
10
11
12 13
325
When real samples were injected, the chromatogram was complex compared to
that of the standard. However, it was easy to pickup our compounds and identify them
by comparing their retention times with standard. The retention times and the peak
areas for the eluted compounds are shown in (Figure 6&7) and given in table 3.
Similarly, all samples collected during the different time intervals were analyzed
by GC following the same procedure and the results are summarized in tables 3 and 4.
Table 3: Retention times and peak areas for compounds recorded in figures 6 and 7.
Sample number 1-a 1-a 2-a 2-a
No. Name RetentionTime
PeakArea
Retention Time
Peak Area
2 fluorine 8.8 1230 8.8 1288
3 phenanthrene 9.9 2200 9.9 1950
6 benzo (a) anthracene 14.5 4675 14.5 5306
7 chrysene 15.8 1980 15.75 3250
10 benzo (a) pyrene 21.9 2800 21.9 2139
12 dibenzo (a, h) anthracene 23.8 1224 23.8 991
Table 4: Concentrations of PAHs (ng/m3) in collected aerosol samples.
PAH name B.a.a B.a.P B.k.f chry d.b.ah.a Flu phen
Total
Avg. 20.5 7.4 10.3 43.6 8.8 71.2 48.3
SD 27.8 11.5 18.5 43.9 8.9 39.2 25.9
A*
Avg 30.3 5.8 14.8 55.6 8.2 83.9 68.2
SD 35.1 5.9 24.5 61.7 8.0 39.1 25.2
B*
Avg 28.0 11.5 13.5 37.5 14.0 82.70 47.6
SD 27.4 17.9 19.9 31.3 10.9 35.9 20.2
C*
Avg 3.3 4.8 2.7 37.7 4.3 47.1 29.1
SD 3.2 6.1 3.0 34.3 4.1 34.0 16.4
t- test
t-test A-B 0.87 0.74 0.89 0.29 0.20 0.95 0.06
t-test A-C 0.04 0.41 0.15 0.20 0.19 0.04 0.00
t-test B-C 0.02 0.09 0.12 0.72 0.02 0.04 0.04
*: Time interval
A: time interval (6.00 am-10 am).
B: time interval (12.00 am-4.00 pm).
C: time interval (7.00 am-10.00 am).
B.a.a: benzo (a) anthracene; B.a.P: benzo (a) pyrene; B.k.f: benzo (k) fluoranthene; chry: chrysene; d.b.ah.a: dibenzo (a, h) anthracene; Flu: fluorine; phen: phenanthrene.
As it can be seen from the table, the predominant PAHs detected in our samples
were the low molecular weight PAHs. These are; phenanthrene, fluorine and chrysene.
These results are in good agreement with the results obtained using LEF. As can be
326
seen in Table 3, the highest total PAHs concentrations were during the first and
second time periods (6.00 am to 4.00 pm), which are the morning and afternoon
periods. T-test was used to check if there is a significant difference between the
concentrations in samples collected from different time intervals. Results indicated the
presence of a significant difference between the C period and both A and B periods.
Concentrations of PAHs in samples collected during the C period were generally
higher than those collected in either A or B. These higher concentrations during this
time period could be attributed to the increased human activities during the daytime
and the increased wind speed during night, which leads to dilution of concentrations in
the atmosphere.
Fluorine was found to have the highest concentration among the detected PAH
(84 ng/m3), while benzo(a)pyrene has the lowest average concentration (7.2ng/m3).
Comparison of the atmospheric data with the literature is one of the essential steps in
the atmospheric studies. Area under study is broadly classified as urban. The urban
areas are ones that are under the direct influence of the local anthropogenic
emissions. Therefore, in order to roughly know the extent of pollution in the area under
study, the result should be compared with literature data in which the pollution level is
known. Comparing the data with data obtained from resembling areas may help in
finding out the unusual results, which could be due to particular analytical problem.
Observed concentrations of PAHs are compared with those found by others in urban
areas. Therefore, literature values were also selected to be from urban areas.
Measured concentrations of PAHs in urban areas are presented together with our
results in table 5.
Table 5: Comparison of observed concentrations of PAHs (ng/m3) with reported literature data.
PAH This study
LahorePakistan
Taiwan
TaipeiChina
RomeItaly
Calcutta India
Fluo 71.2 1.0 138.5 15 - -
Phen 48.3 0.97 94.2 - - 11.2
B.a.a 20.5 5.4 14.2 9 1.27 30.2
B.a.p 7.4 9.3 9.0 1.7 1.74 43.2
B.k.f 10.3 4.61 14.5 1.1 1.19 22.4
Chry 43.6 8.6 50.7 3.3 2.8 32.2
D.b.ah.a 8.8 4.0 4.3 3.2 0.35 12.1
Fe
Fe
Figure 6: GCeach peak ar
Figure 7: GCeach peak ar
1.E+
6.E+
1.E+
2.E+
2.E+
3.E+
3.E+m
v
C chromatogre summariz
C chromatogre summariz
+01
+01
+02
+02
+02
+02
+02
0
gram of pollued in table 3
gram of Samed in table 3
5
2
327
uted air samp3.
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10
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6
7
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15
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10
12
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20
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328
Acknowledgment The authors would like to thank Prof. Dr. Mohammad Al-Qudah and Dr. Natheer
Rwashdeh for their valuable discussion. This work was supported by the Deanship of
Scientific Research and Graduate Studies at Yarmouk University, project No. 017 and
IRDC Canada.
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Academy Press: New York, 1983. [2] United States. Congress. Senate. "Air Quality Criteria": Staff Report Prepared for the Use
of the Subcommittee on Air and Water Pollution, Committee on Public Works, United States Senate", U.S. Government Printing Office: U.S.A., 1968.
[3] Rand, G. M; Petrocelli, S. R., "Fundamentals of Aquatic Toxicology", Hemisphere Publishing Company: New Yourk, 1985, 666.
[4] Irwin, R. J.; VanMouwerik, M.; Stevens, L.; Seese, M. D., Basham W., "Environmental Contaminants Encyclopedia", National Park Service,Water Resources Division: Colorado, USA, 1997.
[5] Pott, F.; Heinrich, U., "International Agency for Research on Cancer (IARC)", No. 104, 1990, pp. 288–297.
[6] Cook, R. H.; et al., "Polycyclic Aromatic Hydrocarbons in Aquatic Environment: Formation, Sources, Fate and Effects on aquatic Biota", NRCC: Ontario, Canada, 1983.
[7] Wehry, E. L.; Rossiter, B.W.; Baetzold, R. C., "Physical Methods of Chemistry", vol. 8, Wiley: New York, 1993.
[8] Remediation and Redevelopment Division, Michigan Department of Environmental Quality, Operational Memorandum (2), October, 2004.
[9] Lu, H. B.; Xie X. S.; Nature, 1997, 385, 143. [10] Weiss, S., Science, 1999, 23, 1676. [11] Wu, S. W.; Ogawa, N.; Ho, W., Science, 2006, 312, 1362. [12] Abu-Zaid, M. E.; Marafi, M.; Maqdsi, A.; Amer, M.; Yousef, Y. A., "Molecules in Physics,
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31, 563. [15] Yousef, Y. A., Optica applicata, 2005, 35, 67. [16] Karcher, W., et al.; "Spectral Atlas of Poly cyclic Aromatic Hydrocarbons", Holland, 1983. [17] Berlman, I. B.; "Handbook of fluorescence spectra of aromatic molecules", Academic
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