International Journal of Environmental Research University of Tehran ISSN: 1735-6865 EISSN: 2008-2304 Vol. 2, Num. 1, 2008, pp. 97-102

International Journal of Environmental Research, Vol. 2, No. 1, 2008, pp. 97-102

¹ Department of Energy, Materials and Energy Research Center,Tehran, Iran
² Garduate Faculty of Environment, University of Tehran, Tehran, Iran
³ Department of Marine Living Resources, Iranian National Center for Oceanography,Tehran, Iran
*Corresponding author: Email-f-halek@merc.ac.ir

Received 26 Jan. 2007; Revised 20 August 2007; Accepted 7 Sep. 2007

Code Number: er08013

ABSTRACT

Polycyclic Aromatic Hydrocarbons (PAHs) are toxic pollutants released by various urban combustion sources. Tehran is the largest city in Iran with a population of about 8 million and it is faced with serious air quality problems. The gas phase samples collected from 21 sites in Tehran area throughout year 2005. The samples‘ PAHs were collected using a SKC trapping consisting of glass cartridge packed with XAD-2 resin supported by two polyurethane foam plugs. Sixteen PAHs were analyzed by HPLC with two detectors (fluorescence; UV-Vis) according to U. S. Environmental Protection Agency methods.The average concentrations of PAHs ranged from 16068.98 µg/m³ for Bahman site to 1000.24 µg/m³ for Nour site. The species that presented higher concentration were Acenaphtylene (2674.74 µg/m³), Naphthalene (2467.71 µg/m³) and Acenaphtene (1245.22 µg/m³). The PAHs with two and three rings were responsible by 87 % of the total concentration among 16 PAHs. A major source of PAHs, in Tehran area is related to traffic and the number of gasoline and diesel vehicles.

Key words: Toxic compounds, Polycyclic Aromatic Hydrocarbons (PAHs), Vapour phase, Vehicle emissions

Polycyclic Aromatic Hydrocarbons (PAHs) are formed by incomplete combustion or high temperature pyrolytic process involving organic matter (Chetwillayachan, et al., 2002). The burning of fossil fuel is one of the main sources of anthropogenic PAHs‘ emission in environmental air. The PAHs are semi-volatile substances at atmospheric conditions and frequently occur both in the gas phase and as attached to particles depending on the vapor pressure of each PAH (Caricchia, et al., 1999; Wingfors, et al.,, 2001; Basheer et al., 2003). Lighter PAHs are found predominantly in gas phase, whilst those with four or more rings are found mainly adsorbed in particulate material (Allen, et al., 1996; Park, et al., 2002; Vasconcellos, et al., 2003). PAHs are considered highly toxic for human beings and several of these compounds are carcinogenic, mutagenic or teratogenic (Dockery, et al., 1993; Santos, et al., 2002; Kavouras and Stephanu, 2002). Although lighter PAHs have weaker carcinogenic/mutagenic properties, they are the most abundant in the urban atmosphere and react with other pollutants to form more toxic derivatives (Park, et al., 2002; Ho, et al., 2002). A major source of PAHs is related to traffic and the number of gasoline and diesel vehicles, particularly for Tehran area (Oda, et al., 2001; Gramotnev, et al., 2003).

There is no study reporting the PAHs in Tehran environment, where people are directly affected by these carcinogenic pollutants. With due attention to correlation of increased human morbidity and mortality with increased ambient pollutants, it was a need focuses on ambient concentration of toxic chemical compounds for the first time and assess PAHs profiles in several sites across Tehran (Cincinelli, et al., 2007). Generally, the aim of the present work is intended to establish a baseline reference for database carcinogenic compounds and aid in regulatory actions of improving air quality in the Tehran.

Tehran with population of more than about 8 million has faced air pollution for a long time. Tehran occupies ~2300 km² at an elevation of 1200 m above mean sea level. It is bordered on the north, northwest, east and south-eastern by high to medium height (4000-1000 m)mountain ranges. (Halek, et al., 2004). In Tehran haphazard urbanization, unprecedented vehicular emissions and inadequate infrastructure development are supplementary factors for the fall in air quality. In this study 21 sampling sites in Tehran were selected to characterize the PAH concentrations in ambient air in Tehran. On the whole, these sites were located in the North, South, East, West and Center of Tehran. The criteria of sites selection were based on different municipality districts that covered throughout of Tehran area. Situation of sites selected in Tehran area is shown in Table 1.

For this study a total of 21 sites were chosen for the time period of January 2005-December 2005. The samples were collected for 8-10 hrs a day, from 8:00 am to 18:00- 20:00 pm. The air inlet was located 1.5-2 m above ground level. The gas phase PAHs were collected using a SKC trapping consisting of glass cartridge packed with XAD-2 resin supported by two polyurethane foam (PUF) plugs. The samples were collected at a flow rate of 1.5- 2 L/min. The sampling device was protected with aluminium foil during the sampling period. The cartridges were stored in a clean screw-capped vial with a Teflon cap liner and placed in refrigerated containers for transportation.

Quantification was performed from HPLC profiles using the external standard method. The external standard was purchased from Supelco containing 16 PAH compounds (EPA 610 PAHs mix) including Naphthalene (Nap), Acenaphtylene (Acy), Acenaphtene (Ace), Fluorene (Flu), Phenantherene (Phen), Anthracene (Anth), Fluoranthene (Flt), Pyrene (Pyr), Benzo (α)Anthracene (BaA), Chrysene (Chr), Benzo[b]fluoranthene (BbF), Benzo [k]fluoranthene (BkF), Benzo[α]Pyrene (BaP), Dibenzo[ah]Anthracene (DBahA), Benzo [ghi]Perylene (BghiP) and Indeno (1,2,3-cd) Pyrene (Ind).

This standard was used at different dilutions to obtain calibration curves for each run. Five point calibration curves for all the target analytes, ranging from 5 to 1000 µg/mL, were obtained (r > 0.99).

A fluorescence detector (RF-10AXL) was set at 280 and 390 nm wavelengths, respectively, for excitation and emission. The Fluorescence detector was unable to detect all of 16 species of PAH; therefore UV and fluorescence detectors were simultaneously used. The UV detector (K2500) was operated at λ= 254 nm. The detectors were adjusted for maximum selectivity for each PAH.

Sixteen PAHs were detected in all the samples at the gas-phase for 2-6 rings PAHs. Concentration of individual compounds was found in the range of 0.76 -10997.15 ng/m³. The total PAHs (PAHs), estimated as the sum of the monthly mean concentrations, ranged between 1000.14 and 11834.00 ng/m³ and the average PAHs concentration for the sampling period was (8089.35) ng/m³. Table 2 shows the 16 PAHs detection limit (LD) of the method and mean of the compounds under study.

Figure 1 shows a typical PAH distribution for the study period, where the low molecular substances like Acy, Phen, Flu, Ace and Anth had a maximum load. As can be observed from the data, Acenaphtylene (2674.74 ng/m³ mean concentration) resulted in a contribution of 33.1 % in mass and was the most abundant PAHs through the collection period. The second compound was Naphthalenewith 30.5 % followed by Acenaphtene of 15.4 %. Figure 2 shows the relative contribution of the individual PAHs in relation to the total mass obtained in the sampling.

Referring to Fig. 2, unfortunately at Bahman site in the south of Tehran area, the atmospheric levels of ΣPAH was 16068.98 ng/m³ and at Nour site in the north western of Tehran, level of these compounds was 1000.24 ng/m³.

Higher PAHs concentrations in Tehran are proposed relative to irregular increased in consumption of fossil fuel combustibles, traffic fleet, vehicle emissions, traffic flow and meteorological factors such as lower mixing layer height, low wind speed, scanty of rainfall and inversion events. Diesel trucks were the major source of lighter PAHs, whereas light-duty gasoline vehicles were the dominant.

As mentioned before the PAHs species concentration was separated considering the low molecular weight PAHs (LM-PAHs), those containing two to three rings (Nap, Acy, Ace, Flu, Phen, Anth), and high molecular weight (HM-PAHs) containing four to six rings (Flt, Pyr, BaA, Chr, BbF, BkF, BaP, DBahA, BghiP, Ind) (Panther et al., 1999; Lee et al., 2002). Of the total analyzed PAHs (8089.35 ng/m³), the low molecular weight PAHs (2-3 rings) were the dominant species, corresponding to 87 % (7038.35 ng/m³) (Naphthalene to Anthracene, average concentration from 2467.70 to 147.70 ng/m³ respectively), while high molecular weight PAHs (4-6 rings) representing 13 % (1051.00 ng/m³) of the total detected PAHs in gas phase (Fluoranthene to Indeno[1,2,3cd]pyrene, 779.20 to 28.39 ng/m³, respectively) (Fig. 3). The individual and total concentration of PAHs as a function of the collection monthly for one year is shown in figure 4. During March-April (20th of March- 20th April) due to the reduction in the number of motor vehicles in transit (Nou Roz - new year holidays) occur a decrease about 83 % of the total PAHs concentrations.

Determination of PAH_S Emission Sources

Vehicular emissions are the result of different sources and produce of unburned, oxidizes of fossil fuels and additives. Many diagnostic ratios between are used to characterize potential emission sources and to distinguish among the PAHs sources as coming from the combustion process. It was also shown that major source of PAHs in Tehran is directly related to the traffic and the number of gasoline and diesel oil burning vehicles. Diesel fuels contain significant quantise of PAHs, and their emission may arise primarily from diesel fuel PAHs surviving the combustion process. Results of PAH analysis indicated that existence of several of the higher molecular weight PAHs (Benzo(α)Anthracene, Chrysene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[ α]Pyrene),Benzo[ghi]Perylene, Indeno(1,2,3-cd) Pyrene confirm role of gasoline fuelled emissions in Tehran’s atmosphere. Energy uses of residential buildings across Tehran (Iran) are dominated by natural gas with a small amount of electricity and heating oil. Average PAHs concentrations measured in all of stations were compared to different PAHs profiles measured previously for gasoline and diesel engine exhausts. The ratio of heavy PAHs in gasphase to these of light one has found to be 0.149. These profiles showed good agreement with previously published profiles for the vehicular source (r = 0.94) (Oda, et al., 2001; Gramotnev, et al.,2003; Halek, et al., 2004; Tao, et al.,2006). This result also underlines and confirms the importance of BaP as a prominent carcinogenic compound of PAHs mixtures in air. The contribution of the carcinogenic potency of BaP alone is in the range of 49.6- 76.3 % of the total carcinogenic activity.

In this paper for the first time, a detailed experimental investigation of the evolution of gasphase PAHs has been carried out in Tehran area.

Acenaphtylene appears asthe most abundant PAHs, followed by naphthalene and Acenaphtene. A decrease in PAHs concentration was detected during in Nou Roz days by reason of decrease in vehicles population. The PAHs source fingerprint identified in this study was obtained from motor vehiclesespecially diesel emission.We obtained that PAHs concentration in Bahman (16068.98 ng/m³) and Alghadir (13717.82 ng/m³) sites are at least ten times higher than Nour site (1000.24 ng/m³). It was also shown that major source of PAHs in Tehran is directly related to the traffic and the number of gasoline and diesel oil burning vehicles. It is also found, from the abundance of the 3 ring PAHs in all the stations throughout the sampling period in Tehran, the role of heavy vehicles and gas oil burning, to be 60-70 % is more than light ones in producing the important pollutants. Certainly, this information can be aid in regulatory actions of improving air quality and health risk assessment in Tehran and other mega cities in Iran in future.

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