Profile of Atmospheric PAHs in Rawalpindi , Lahore and Gujranwala Districts of Punjab Province ( Pakistan )

In this study, polyurethane foam passive air samplers (PUF-PAS) were deployed to evaluate the atmospheric concentration levels and ambient exposure of polycyclic aromatic hydrocarbons (PAHs) in Gujranwala, Lahore and Rawalpindi districts of the Punjab Province (Pakistan). The PAHs were extracted from the PUFs disks using Soxhlet extraction assembly, and were further concentrated using rotary evaporator, purified on a column, packed with alumina/silica, and eluted with a solution of dichloromethane:hexane (1:1 v:v). The PAHs quantification was carried out gas-chromatograph equipped with a mass-spectrometer (GC-MS). Regression scatter plots and molecular diagnostic ratios were used to identify and characterize the emission of PAH species from different sources. Among all detected PAHs, a high concentration of naphthalene (Naph) was observed in Lahore (327 pg m) and Rawalpindi (316 pg m) cities followed by phenanthrene, banzo(a)pyrene, pyrene, benzo(b)florenthene and benzo(k)flourenthene. Our findings revealed that the low molecular weight (LM)-PAHs in Rawalpindi and Gujranwala cities could have possibly originated from a local petroleum refinery and vehicular emissions respectively, whereas the high molecular weight (HM)-PAHs observed in Wazirabad, could be largely related to both biomass and traffic emissions. Results also showed that ~88 percent of the atmospheric PAHs could be attributed to the wood combustions (R = 0.88), out of which more than 50 percent of wood combustion were possibly with the brick kiln sector (R = 0.53).


INTRODUCTION
Polycyclic aromatic hydrocarbons (PAHs) are well known for their adverse health outcomes in human.Recently, PAHs have been included in Convention on Long-range Tranboundary air pollution on persistent organic pollutants (POPs) (UNEC, 1998) and are widely studied by scientific community because of being among the group of first possible carcinogenic pollutants (WHO/IPCS, 1998; Kamal et al., 2015a).The discovery of mutagenic and carcinogenic properties of several PAHs have brought them under the serious consideration of scientific community (Nisbet and LaGoy, 1992;Taioli et al., 2007).Although there are hundred of different PAH congeners but U.S. EPA selected 16 PAH congeners as "priority pollutants" in 1970s (Nisbet and LaGoy, 1992;Kamal et al., 2014).Since the PAHs with high molecular weight possess carcinogenic proprieties, they have been categorized as confirm carcinogen (Class-1), probable carcinogenic (2A) or possible carcinogenic (2B) to human (IARC, 1983(IARC, , 1987;;Shi et al., 2005;Kamal et al., 2014).In all over the world (e.g., USA, European Union, China, Italy, UK), permissible limits of BaP emissions have been introduced to control PAHs emissions (Wu et al., 2014 and reference therein), however there is a wide gap in PAHs control in some developing countries.
PAHs that originate either from anthropogenic activities such as combustion processes can be easy inhaled and ingested by human being (Simcik et al., 1998;Lohmann et al., 2000).A large amount of PAHs are released during incomplete combustion of organic materials (Zhang and Tao, 2009;Ma et al., 2010).Similarly, as the combustion of fuel in the automobiles, account for ~5% and domestic coal account for ~4%, globally, while industrial emission remains < ~10%.The country-wide frequencies of biomass and fuel consumption vary with their economic conditions and population.For instance, the biofuel is a major source of energy (~90%) in developing/rural regions of the world and accounts for a large proportion of PAHs emission (Zhang and Tao, 2009).The combustion of biomass material accounts for ~57% of global emission of PAHs.In addition to the combustion processes, the widespread distribution of the atmospheric PAHs is also facilitated by their physicochemical properties, e.g., low reactivity and vapor pressure, (Nam et al., 2003).
Some studies conducted in the developing countries have demonstrated that the urban PAHs concentrations were higher than those in the surrounding rural areas; however, due to insufficient data from such regions (Li et al., 2014), the conclusion remains largely immature.There is a dire need to monitor PAHs emissions in the developing countries like Pakistan, where such phenomenon is not studied extensively.In Pakistan there is only one study on the concentration of atmospheric PAHs available so far, (i.e., Smith et al., 1995), in which the environmental PAH monitoring was conducted at three sites in Lahore city of Pakistan.The study, was based on the results of an active sampling device, which showed that the concentration of PAHs was quite high and comparable to those in some Indian cities.However, no detailed study was ever conducted in this reagion everafter.In recent years, the passive air samplers (PAS) based on sorbent disks of polyurethane foam housed in stainless steel protective chambers are widely used for the sampling of atmospheric persistent organic pollutants.These devices do not require any electric pump and can be installed in many sites, and provide high retention capacity for many organic compounds (Harner et al., 2004;Choi and Spengler et al., 2014).
The use of PAS device to monitor POPs concentration levels is of beneficial in the energy deficient countries like Pakistan where large proportion of energy (around ~27%) is derived from the combustion of biomass fuel (~76% of which is shared by household biomass use), and it is one of the countries of the world where biomass utilization is increasing at the rate of ~2% per annum (Butt et al., 2013).It is expected that due to the lack of sound pollution control planning in some major cities of Pakistan (i.e., Lahore, and Rawalpindi) (von Schneidemesser et al., 2010), emissions are largely associated with traffic exhaust and high influx of heavy traffic and the problem will continue to increase in the future.In addition to traffic pollution, in cities like Gujranwala and adjacent towns (i.e., Sohdra, and Wazirabad) they are also facing high pressure of industrial as well as conventional fossil fuel combustion activities in the residential areas.
Considering the above discussed scenario, this study was designed to evaluate the concentration of atmospheric PAHs in three highly populated districts (i.e., Rawalpindi, Lahore and Gujranwala) of Punjab province (Pakistan).Moreover, source apportionment of the ambient PAHs was also performed and discussed.

Deployment of Passive Air Samplers for PAH Monitoring
The PUF disks housed in a stainless steel protective air sampling device chambers were installed in various stations.
The PUF disks (having a diameter of 14 cm, 1.3 cm thickness, and 0.02 g cm -3 density) were wrapped in a sterile aluminum foil and sealed in zip-lock bags for transportation to the sampling sites.For PAHs monitoring in ambient air, several stations were selected in the major cities which were under surveillance in this study.We deployed PAS in three districts for consecutive 56-days periods (Fig. 1).
Rawalpindi and Islamabad are twin-cities and far away from rest of the cities and are surrounded by neighboring Margallah-Hills, and represent less polluted areas of urban/ sub-urban population.The Wazirabad, Sohdra are small towns within the district Gujranwala, and are surrounded by the rural areas, while Lahore is a very old and one of the mega cities of Pakistan.For comparison, the districts were classified into three zone based on the known anthropogenic activities in these areas; these zones were classified as zone-A (Rawalpindi and Islamabad twin cities) where there is no extensive industrial or agricultural activities, zone-B (Gujranwala, Sohdra and Wazirabad) the zone is characterized by agricultural and industrial activities, zone-C (Lahore city) the zone represents districts and popular cities with high-traffic pollution and industrial activities.
The analysis of PAHs in each sample was carried out using 1 µL (in split less mode, and 10 min solvent delay time) on the Gas-chromatograph (Agilent 7890) equipped with a capillary column (DB-5MS, 30 m, 0.25 mm, and 0.25 µm) and a mass-spectrometric detector and (Agilent 5975-Mass Selective-Detector ).The temperature of the oven was initially 60°C, for one minutes, and was then raised up to 290°C (rate of change was 3 °C min -1 held for 20 min).The temperature of transfer lines and that of the injector was 300°C and 290°C respectively.The mobile phase used was a carrier gas (high purity helium, with a flow rate of 1.83 mL min -1 ).

Quality Control and Quality Assurance (QC/QA)
To ensure good accuracy and analytical precision, the PAHs standards were run on daily basis, which showed that the average standard deviation of the instrument analyses was equal or less than ± 10%.The PUFs samples were spiked with 1000 ng of deuterated PAHs (3-5 replicates).The recovery standards used (including the chrysene-D 12 , perylene-D 12 , acenapthene-D 10 and phenanthrene-D 10 ), ranged between 76% and 87%.The recovery percentage of deuterated PAHs ranged between 76 and 87%, while that of surrogate-PAHs was 93 ± 13% for benzo(a)pyrene-d 12 , 97 ± 12% for fluoranthene-d 10 , 94 ± 11% for p-therpenyl-d 4 .We also analyzed the field blank samples (a set of 6-field blanks) to eliminate the chances of background contamination.The method detection limits (MDLs) were the average values of the blanks, ± 3 times the standard deviations of the blanks.Three times of the instrumental detection limit (IDL) were used for calculating the MDLs.The IDL values were calculated using the lowest standards and extrapolating to the corresponding amount of analyte that generates a signalto-noise ratio of 3:1.All target compounds detected in the samples, and lab-blanks were under the IDLs.The data reported in this study were not corrected by the recoveries.

Coefficient of Divergence
The coefficient of divergence (CD) was used to identify the similarities between the profiles of PAHs at two different sites (e.g., city wise comparison).The generic formulae used for CD calculation was as follows The j, and k represent profile of PAHs in tow different sampling sites, p shows the number of target compounds, x is the average concentration of the component (Wongphatarakul et al., 1998).The value of CD < 0.269 reflects a probable divergence between particles between two cities/zones, a CD value > 0.16 suggests a commons source in two sites under discussion (Wongphatarakul et al., 1998).

Statistical Analysis
All the concentrations of individual and total PAHs detected in air samples and diagnostic ratios calculated for source identification have been presented as mean ± standard deviation, median, minimum and maximum values while all the PAHs results have been presented in pg m -3 .Sampling sites were divided into 3 zones (represented three districts i.e., zone-A, B and C) based on hypothesized low medium and high levels of pollution in different cities.Numerical data was also tested for any deviation from normality using the Kolmogorov-Smirnov (K-S) normality test.Comparative analysis was performed using independent samples t-test among cities/zones.All statistical analyses were performed using MS-Excel and SPSS statistical software (version 20.0).

PAHs Profile in the Atmosphere of the District
Rawalpindi/Islamabad and Lahore Among PAHs congeners, high concentration of Naph was observed in Lahore (327 pg m -3 ) and Rawalpindi (316 pg m -3 ) cities. PAH-congeners such as Phe, BaA, Pyr, BbF, BkF were dominant in Lahore > Rawalpindi > Islamabad.The concentration of the Naph was high in the Rawalpindi (317 pg m -3 ), as compared to that in the Islamabad city (261 pg m -3 ) (p = 0.03) (Table 2).The Naph (327 pg m -3 ), Acy (10 pg m -3 ) Fl (56 pg m -3 ) BaA (246 pg m -3 ) were also considerably higher in the Lahore city than those detected in the atmosphere of Islamabad.Lahore city is a densely populated and highly polluted because of old vehicular traffic.Lahore receives emissions from industrial activities, brick kilns, and use of coal/wood for cooking purposes in villages in the suburban towns.All these factors together contribute to the air pollution and the atmospheric PAHs emissions.In fact, according to World Health Organization (WHO), the City Lahore is facing high level of organic carbon (OC) contents and the levels of particulate matter (PM) were above the WHO guidelines (Stone et al., 2010).The PM bound OC in this city could be attributed to the combustion of biomass fuel and petroleum in motor vehicles (Stone et al., 2010).In Lahore city; the passive sampling station was selected in the Chung Khurd area.In this area, the HM-PAHs such as IP, BghiP, BaA and DBA were observed in high concentration in the atmosphere of Lahore city, which could have originated from gasoline and diesel exhaust.The concentration of Phe, Fla, IP and BghiP is usually high in the vehicular emissions exhaust (de Andrade et al., 2010).Similarly, other PAH congeners including the BghiP, Cor, Phe are also present in the motor vehicular exhaust emission (Ravindra et al., 2006), moreover; the Phe was high in Rawalpindi and Lahore and high Pyr concentration in all three cities represent a mix contribution of anthropogenic origin (i.e., oil/biomass combustion and vehicular exhaust emission) in these cities (Ravindra et al., 2008).In Lahore, high concentration of BghiP and IP indicated gasoline and oil combustion (Kwon and Choi, 2008).In addition, we observed high concentration of several LM-PAHs in Rawalpindi city, including Naph, Phe, which could be originating from the petroleum refinery located within the city suburbs, in particular, from the functional incinerator of this refinery which could be is a very important source of volatile PAHs and particulate matter (PM) in these areas (Kamal et al., 2013(Kamal et al., , 2015b)).
were dominant in both cities, however, in Gujranwala, the contribution of vehicular exhaust and gasoline was more prominent.
The level of PAH-congeners in Wazirabad showed a mixed source of LM-PAHs and HM-PAHs as the comparative data showed that PAH-congeners were high in Wazirabad versus Gujranwala.High concentration of 5-rings PAHs indicated the industrial emission especially from the combustion activities.In general, the profile of PAHs in Wazirabad showed more HM-PAHs emerging from both traffic and combustion-emission.Higher values of Chry and BkF revealed a possible emissions from the coal (Smith and Harrison, 1998;Ravindra et al., 2008) and diesel combustion (Kwon et al., 2008), whereas BghiP also mark gasoline combustion emissions (Kwon et al., 2008 and reference therein).The Fla, Phe, IP, BghiP are markers of fossil-fuel combustion (Kwon et al., 2008).The mobiles sources, especially heavy-duty diesel trucks emit light weight PAHs (Naph, Fla, Pyr) (Marr et al., 1999).Moreover, the HM-PAHs (e.g., BaP, DBA) are usually dominant in the exhaust emission of the light-duty gasoline-powered vehicles (Miguel et al., 1998;Wingfors et al., 2001).In addition to this, the 4-and 5-rings PAHs as reported by Marr et al. (1999) are also released in the exhaust emission of the light-duty vehicles, similarly heavy-duty vehicle mostly release 3-rings PAHs.
Both Sohdra and Wazirabad towns are 42 and 36 km away from Gujranwala city (both are a part of District Gujranwala), respectively.A likely explanation of the profile observed in the atmosphere of these cities is that, the Gujranwala is one of the major industrial cities of Pakistan (less the 75 km away from Lahore) which is located close to grand trunk-road (GT-road) of Pakistan (Kamal et al., 2014a, b).In addition to Lahore and Gujranwala cities, the Wazirabad and Sohdra also possess a segment of rural population, where the use of coal/wood and other biomasses is common for cooking purposes.There are many brick kilns located in the vicinity of Gujranwala, Wazirabad and Sohdra, where the wood/coal and a huge amount of cheaper fuel, including scrap rubber/tyre pieces to fire brick kilns.In many other cities of Pakistan, the brick kiln industry together with the presence of large segment of rural population where daily combustion of biomass fuel is common, which releases additional amount of PAHs on daily basis, and the atmospheric PAHs concentration in these areas is further supplemented by the heavy traffic exhaust.
We used the coefficient of divergence analysis (CD) in order to evaluate the divergence of PAH components between different zones, to identify whether the PAHs had the same source of origin and vice versa.According to the Wongphatarakul et al. (1998); a CD value < 0.269 reflects a probable divergence between particles in two zones.Considering the proximity of zone-B and zone-C, it was suspected that the source of PAHs in these zones could be similar; however, a value of CD = 0.55 (Table 1) approaching 1, showed that the two zones received PAHs from independent source, which could be high industrial and traffic input in the zone-B and Zone-C respectively.
The concentration of ∑PAHs in the ambient air of three districts (Fig. S1 in supplementary file) was regressed against the number of brick produced per annum as reported by Tahir et al. (2010).The results provided further evidence of wood combustion activities and influence of the brick kiln sectors in three districts.According to the results ~88 percent of the atmospheric PAHs could be attributed to the wood combustions (R 2 = 0.88), whereas more than 50 percent of wood combustion could be related to the brick kiln sector (R 2 = 0.53).

Source Apportionment of Atmospheric PAHs Using Diagnostic Ratios (DRs)
We used regression scatter plot to indentify the traffic driven (LM-PAHs) PAHs from those generated during the combustion of biomass fuel (mostly HM-PAHs).Figs.S1-S4 shows that there was a strong negative association between the ∑LM-PAHs/HM-PAHs ratios and the ∑COM-PAHs which showed that the large proportion of the PAHs emission in these cities could be associated with biomass mass combustion activity (further confirmed by strong association between ∑PAHs and ∑COMB-PAHs) (see Figures in S1).
The molecular diagnostic ratios (DRs) of PAHs are commonly used as a tool for the identification characterization/ identification of PAHs emission sources (Yunker et al., 2002); in a certain environmental compartments, the profile and composition of PAHs reflects the individual source of emission (Wang et al., 2007).It is known that the concentration different PAHs congeners depend upon the source from which they are originated.The DRs were used in this study was based on the previous knowledge and current concentration of PAHs congeners detected in air.The ratios which are most commonly used were adopted from different literature studies to gain the most relevant qualitative information on PAHs sources (See also Fig. S1 in the supplementary materials S1) (Table 4).
The general profile of PAHs represents that the cities, where low pollution was detected, had a high load of LM-PAHs.The transition point of combustion and petroleum sources of 0.1 is taken for an Ant/(Phe + Ant) ratio is very crucial in determination of sources, i.e., value of < 0.1 indicates and input of patrogenic sources, while a ratio of > 0.1 represent pyrogenic source or, combustion of petroleum, wood/coal, etc.According to our result (Fig. S1; Table 4) city Lahore, Rawalpindi and Islamabad, all had values of this ratio < 0.1 indicating a dominance of petrogenic sources in these cities.The Ant/(Phe + Ant) ratios was > 0.1 in Gujranwala, Sohdra and Wazirabad cities, which represented a dominance of combustion sources possibly in brick kiln unite in the surrounding areas and use of wood/coal for cooking purpose by a large proportion of rural/sub-urban population in the surrounding areas (Fig. S2).
The of Fl/(Fl/Pyr) between 0.4-0.5 represents an input of petroleum combustion (Table 4) stands for the petroleum input, 0.4-0.5 for petroleum combustion (vehicle, crude oil and liquid fossil fuel), while > 0.5 accounts for the combustion of coal/wood and other biomass (Yunker et al., 2002).The results of calculated diagnostic ratios in Sohdra Wazirabad, Rawalpindi, and Lahore city indicate that PAHs originates mainly from the combustion of petroleum

Table 1 .
Table 1-4.The PAHs Diagnostic ratios and the concentrations of individual and total PAHs in the atmosphere of three sampling zones (Punjab).

Table 2 .
Concentration of individual PAH congeners detected in the atmosphere of Rawalpindi, Islamabad and Lahore cities of Punjab (Pakistan).

Table 3 .
Concentration of individual PAH congeners detected in the atmosphere of Sohdra, Gujranwala and Wazirabad cities of Punjab (Pakistan).

Table 4 .
Sum of PAHs concentration (combustion origin and ∑7Carcinogenic PAHs) and diagnostic ration in the atmosphere of sampling sites.