GIS-Assisted Investigation on Dispersion of BTEX in Industrial Regions of Zarghan, Iran

Introduction
BTEX is a group of polycyclic aromatic hydrocarbons including benzene, toluene, ethylbenzene and
xylene. Benzene is released to the atmosphere by both natural and anthropogenic activities. Benzene is emitted
to the atmosphere mainly through the petroleum and petrochemical industries. The chronic exposure to
benzene may cause damage to kidneys, liver, lungs, heart, and nerves and also degrade DNA. Benzene
is a group (I) carcinogen. Toluene is used in many industries as a solvent. The exposure to low-tomoderate
levels of toluene can cause dizziness, drowsiness, nausea and hearing loss. The exposure to high
levels of toluene can cause permanent brain and speech damage, unconsciousness and even death.
Ethylbenzene is used in the petrochemical industries. It is also used in industries including gas, oil,
solvents, pesticides and dyes. Short-term exposure to high level of ethylbenzene can cause symptoms
such as respiratory irritation and neurologic effects. The long-term exposure to ethylbenzene affects
the blood, liver and kidney. It is classified as a possible human carcinogen (2B) by IARC. Xylene is an
aromatic hydrocarbon which is usedw ith benzene and toluene as a catalytic reform er in extraction and oil
refineries. Xylene is a major component of BTEX and is used as a fuel reformer. The inhalation of xylene affects
the nervous system.
Active sampling needs an air sampling pump to actively collect the air through a filter. However, passive
sampling does not require a pump and the gases in the air are collected by diffusion. Passive diffusive air
sampling is simple with high precision method widely used to monitor large-scales air pollution. Geographic
Information System (GIS) is a powerful tool to assess the contribution levels of BTEX sources. Haddad et al.
(2005) used passive sampling to measure BTEX around gas stations in Shiraz.
Since the industrial area of Zarghan is affected by numerous air pollution sources, the rapid and precise
monitoring systems are absolutely essential to detect and quantify polluting sources. Therefore, the objectives of
this study are to (i) determine the dispersion level of BTEX using passive diffusive air sampling and GIS
techniques and (ii) assess the contribution level of generating sources of BTEX in the urban areas.
Material &Methods
Zarghan is located 25 Km northeast of Shiraz, nearby Shiraz -Tehran highway. The town is also surrounded by
many different air pollution sources. Industrial complexes are located about 10 Km from Zarghan. In addition,
the mountain in the east side of the town blocked the air flow through the town.
We used a diffusive sampler to adsorb BTEX in the air by a tube consisting of adsorbent material. BTEX
entered into the adsorbent tube by molecular diffusion. The adsorbent samplers were installed at the elevation of
3 to 4 meters from the ground for the period of 17 days (March 2012). After the adsorption period, the sampler
tubes were sealed and returned to the laboratory for further analysis. After collecti ng the specimens, they were
sent to Pasam Company in Switzerland for determination of BTEX. The extraction was done by carbon disulfide
(CS2). Ion chromatography was used to analyze BTEX.
Since many sources of air pollution are located in the Zarghan residential area, the boundary condition
sampling points were selected by mesh. Due to the small size of the study area, 10 points were selected and one
sample was collected at each point.
An image of the coverage area was obtained by Google Earth software. Geographical coordinates of 4 points
of suitable dispersion were determined by the software and used in an Excel file as the ground reference. Using
ArcGIS techniqus, the image was processed as the georeferenced map and the result saved in TIFF format with a
pixel size of 5 m. The data obtained from sampling of BTEX were interpolated using the passive sampling
method with different methods such as Inverse Weighted Distance to the exponent of 2 (IWD)2, natural nearest
neighbor. File Format (TIFF) is a raster image format with a pixel size of 5 m for each specimen (with at least 10
sample points). All interpolated layersw ere then extracted by the border of sam ple point’s area to perform
interpolation for all layers in the same extent. The geographic coverage area of BTEX concentration has been
studied using different methods of Nearest Neighbor (NN), Inverse Distance Weighted (IWD), and Kringing.
BTEX pollution maps were prepared using passive sample interpolation.
Discussion and Conclusion
The ambient air quality guidelines for the annual concentrations of benzene in 2005 and 2010 are 10 􀈝gm-3 and
3.6 􀈝gm-3, respectively. In most of the sampling stations, benzene concentration was in the standard limit (2.3
􀈝gm-3 to 4.8 􀈝gm-3), but the concentrations in the following four stations were considerably high.
1. Shiraz oil refinery sampling station with benzene concentration of 21.5 􀂗gm-3
2. Central old square with benzene concentration of 7.2 􀂗gm-3
3. Dudej with benzene concentration of 5 􀂗gm-3
Data showed that Shiraz oil refinery sampling station with the maximum toluene concentration of 30 􀂗gm-3 is
much lower than the 24-hour EPA standard limit. In the rest of the sampling stations, toluene concentrations
were lower. The average concentrations of toluene in residential areas of Canada were ranged from 11.5
to 34.4􀈝gm-3 which is same as the range of concentration observed in Zarghan. The current study showed
that the concentration of xylene and ethylbenzene in all of the stations were much lower than the harmful levels.
The odor of xylene can be recognized in the air at the concentration of 0.008 ppm. Therefore, during the
maximum hourly pollution (inversion condition), the concentration of xylene is twice the average and
those who live near the mountain areas are able to detect its odor.
The GIS interpolation showed that Shiraz oil refinery is the most important sources of benzene dispersion in
the study area. The relatively high concentration of benzene (21.5 􀂗gm-3) is dispersed in an area where is
confined in a radius of 1.5 Km from the refinery. Fortunately, Zarghan residential areas are not located within
the affected zone, but according to Kringing and IDW interpolation, the concentration of benzene reached to the
amount of 7.2 􀂗gm-3 in the old central square which is located in the center of the city. As seen in the Kringing
interpolation, Shiraz-Tehran highway is not a major source of benzene pollution, but it is expected to have a high
concentration of benzene near the mountain area. The four red stripes represents the high concentration of
toluene belong to Shiraz oil refinery, Zarghan, industrial Park and the highway. The nearest neighbor (NN)
interpolation method showed the effects of Shiraz-Tehran highway more clearly. The pollution due to
ethylbenzene produced by the refinery is extended to a radius of 4.5 Km from the refinery. In addition, this is
evident in the red zone of the industrial park and also in the old part of the city near the m ountain. Generally,
data show exactly the same dispersion for all 3 isomers of xylenes. Comparing the various interpolation methods
used in the study, the IDW method shows the pronounced role of industrial zones while the Nearest Neighbor
interpolation method indicates that the role of the highway is of a greater importance in Zarghan xylenes
pollution. The highest concentration of air pollutants expected to occur in the area surrounded by the
mountain. Therefore, the wind direction influences the general movements of the pollutants. According
to the GIS maps, the main source of air pollution produced by Shiraz oil refinery is significantly
concentrated in the old central square station near the mountain area. Since there is no other air pollution sources
in the area, the reason for increasing air pollution might be due to the trapping of contaminants near the
mountain area and blocked the air flow. The analysis of regression demonstrated that there is a linear
relationship between the concentration of pollutant at Old Central Square and the concentration in the oil
refinery with the regression coefficient of 0.98.