INTRODUCTION:

Benzene, toluene, ethylbenzene, and xylene (BTEX) form an important group of aromatic volatile organic compounds (VOCs). BTEX play a vital role in the tropospheric chemistry and pose health risk to human being.¹ These compounds play an important role in the formation of ozone and other photochemical oxidants in the troposphere.²The International Agency for Research on Cancer, classified benzene as a carcinogenic compound, where it is emitted mainly from petrol-fuelled cars, and thus, it is found in all urban area.^3-4

Benzene is enlisted as Hazardous Air Pollutants (HAPs) in the US Clean Air Act Amendments (CAAA) of 1990.⁵ Benzene present in the urban and industrial atmosphere is essentially as a result of human activities, arising mainly from motor vehicle exhausts and other combustion processes utilizing fossil fuels, petrol storage and distribution, solvent usage and other industrial processes.^6-7 However, as its toxic effects became more apparent, it was ever more tightly regulated and, where possible, substituted by less hazardous compounds.⁸

The major route of exposure to benzene is through inhalation of gasoline vapours by respiration. Long term exposures to high levels of benzene causes cancer of the tissues that form white blood cells.⁹ As per the auto fuel policy of Govt. of India, 2001, buses, taxis and auto rickshaws have switched over to CNG as fuel and benzene content in petrol has been reduced to 1%.

Further, Russian Federation guideline values for benzene are 300 µg/m³for 20-30 minutes and 100 µg/m³ for 24 hours. The annual European Union limits for benzene is 5 µg/m³.¹¹ Under the provisions of the Air (Prevention and Control of Pollution) Act, 1981, benzene has been included in the fourth version of the National Ambient Air Quality Standards, November 2009, by the Central Pollution Control Board, India.¹⁰ Determination of baseline status of benzene in ambient air has been started in all environmental impact assessment projects. The present study was conducted with the objective to determine toxic benzene emissions at high density traffic junctions and major petrol filling stations in an urban city of Nagpur, India. The concentrations of benzene in the ambient air were also measured at some residential sites to know the impacts of traffic junctions and petrol pumps on urban air quality and associated health risk to the local population.

Experimental:

Study area:

Nagpur city is second capital of Maharashtra state and popularly known as orange city. Nagpur city is growing faster with population and industries. The site is bounded 21º 8' 55"N latitude and79º 4' 46"E longitude with an altitude of 312.42 m above mean sea level. Fig. 1 shows location of the sampling site. It has a tropical wet and dry climate with dry conditions prevailing for most of the year. Nagpur city receives an annual rainfall of 1,205 mm from monsoon rains during June to September. The highest recorded temperature in the city was 48.6^ºC on 26 May 1954, while the lowest was 3^ºC. The annual humidity ranges from 10 - 88%.

Sampling and analysis:

Ambient air quality samples were collected during the period from March 2011 to May 2011. Sampling was carried out by active grab sampling method using a battery-operated pump. Air samples at each of the sampling sites were collected in 10-L tedler bags. At the end of each sampling round, samples were transported to the laboratory and analyzed. The external calibration standard Span gas was purchased from Chemtron Science Laboratory, Mumbai, India and was used for calibration. Samples were analyzed by VOC 71 M Gas Chromatography VOC Analyzer with PID detector. During each sampling round, prior to the sampling, the sampling bags were flushed twice with ultrapure nitrogen gas. Quality assurance and quality control measures were taken.

Results and discussion:

Meteorological conditions:

Climatological Tables of Observatories in India, published by India Meteorological Department (IMD), were used to obtain climatological normals corresponding to study area for summer season, 2011. The 24 hourly wind rose shows predominant winds primarily from W direction as well as from NW, WNW, SW and WSW directions with significant occurrence of wind speed in the range1-8 m/s (Fig. 2). Accordingly, the impact zone will be spread in E direction as well as SE-ESE-NE-ENE sector during study period. The wind speed and direction had an influence on the distribution of concentrations of Benzene. The average calm condition was 25 % of time and the average wind speed was 6.5 m/s during study period.

Figure 2 : Windrose diagram for Nagpur City (Study Period)

Table 1 : Mean concentration with Standard Deviation of Benzene at Traffic Squares

Sr. No.	Sampling Locations	Benzene (mg/m³)
Sr. No.	Sampling Locations	Minimum	Maximum	Average±Standard Deviation
1.	Law College	0.6	13.1	7.6±4.6
2.	Shankar Nagar	2.6	62.8	22.2±19.7
3.	Hingana Naka	2.9	39.6	18.6±15.6
4.	Wadi Naka	2.9	61.2	30.3±22.5
5.	Chhatrapati Square	3.2	6.7	4.7±1.2
6.	Medical Square	2.6	9.9	6.9±2.2
7.	Jagnade Square	1.4	5.4	4.4±1.3
8.	Indora	0.6	23.5	11.4±8.2
9.	Mankapur	3.5	28.4	12.0±9.4
10.	Jhansi Rani Square	3.5	33.4	13.1±9.8
11.	Smruti Takies Square	2.6	6.4	4.2±1.3
12.	Gandhibagh	5.1	74.6	28.2±23.1
Mean				13.6

Traffic Junctions:

Monitoring of benzene was carried out approximately 50-100 m distance from the traffic squares. The minimum, maximum and average concentrations of benzene along with standard deviation were presented in Table 1. The variation of benzene concentrations at traffic junctions were shown in Fig. 3. The minimum concentration of benzene ranged from 0.6 to 5.1 µg/m³, maximum in the range of 5.4 to 74.6 µg/m³. The mean concentration of benzene for all the locations together was 13.6 µg/m³.

Figure 3 : Variation of Benzene at Traffic Squares

Among the traffic junctions, Smruti talkies (4.2 µg/m³) showed the least concentration of benzene followed by Jagnade square (4.4 µg/m³) and Chhatrapati square (4.7 µg/m³). The lower concentrations at these locations can be purely due to the vehicular traffic. The benzene concentrations at Medical square (6.9 µg/m³) and Law College (7.6 µg/m³) were due to vehicular traffic as well as petrol filling stations which are located at 100-200 m distance from the traffic junction. At Indora and Mankapur concentrations of benzene were observed as 11.4 µg/m³ and 12.0 µg/m³ respectively. The higher concentration at Mankapur can be due to the location of the junction, which is located on the National Highway-7. Wadi Naka (30.3µg/m³) showed maximum concentration of benzene. High concentration at Wadi Naka can be due to heavy traffic flow and nearby petrol filling station. About 7800 vehicles play per hour at this location. The locations like Gandhibagh (28.2 µg/m³) Shankar nagar ( 22.2 µg/m³), Hingana Naka (18.6 µg/m³) and Jhansi Rani square (13.1 µg/m³) showed much higher concentrations of benzene. Large numbers of passenger auto-rickshaws were travel at these traffic junctions. Majority of the auto-rickshaws use kerosene along with the petrol as a fuel. The combustion of these adulterated fuels may contribute benzene at these locations.

Figure 4 : Variation of Benzene at Petrol Pumps

Petrol Filling Stations:

The concentration of benzene was monitored at the centre of the petrol pump where vehicles halt for refueling. Petrol filling stations showed highest concentrations of benzene among all the categories. The average, standard deviation, minimum and maximum concentrations of benzene were given in Table 2. The variation of benzene concentrations at petrol filling stations are presented in Fig. 4. The minimum concentration of benzene was observed in the range of 2.9 to 13.4 µg/m³ while the maximum concentration of benzene ranged from 11.5 to 73.7 µg/m³. The mean concentration of benzene at all the petrol filling stations together was 20.0 µg/m³.

Table 2: Mean concentration with Standard Deviation of Benzene at Petrol Pumps

Sr. No.	Sampling Locations	Benzene (mg/m³)
Sr. No.	Sampling Locations	Minimum	Maximum	Average±Standard Deviation
1.	Law College	7.7	30.0	19.0±7.8
2.	Shankar Nagar	7.7	33.8	19.7±9.5
3.	Hingana Naka	13.4	46.9	30.7±11.6
4.	Wadi Naka	11.8	73.7	31.9±25.9
5.	Medical Square	8.9	33.8	19.5±9.2
6.	Burdi	3.8	11.5	7.6±2.7
7.	Sadar	2.9	17.5	10.2±5.5
8.	Gandhibagh	9.3	35.7	20.8±9.2
Mean				20.0

Burdi (7.6 µg/m³) showed the least concentration of benzene followed by Sadar (10.2 µg/m³). The higher concentration of benzene was observed at Wadi Naka (31.9 µg/m³) followed by Hingana Naka (30.4 µg/m³), Gandhibagh (20.8 µg/m³), Shankar Nagar (19.7 µg/m³), Medical Square (19.5µg/m³) and Law College (19.0µg/m³). The higher concentrations at these locations can be due to more number of petrol and diesel filling units. The very high concentrations at Wadi Naka and Hingana Naka can be due to the location of the sites. These petrol filling stations are located outside the city limits and the prices of petrol and diesel were less. Therefore, large number of vehicles comes for the refueling of fuel at these locations.

Residential Areas:

The concentrations of benzene were also determined at four residential locations namely Burdi, Dharampeth, Seminary Hills and Gorewada. The minimum, maximum and average concentration of benzene along with their standard deviation was given in Table 3. The minimum concentration of benzene ranged from 0.6 to 2.9 µg/m³, maximum in the range of 1.6 to 6.4 µg/m³. The mean concentration of benzene for all the locations together was 13.6 µg/m³. The mean concentrations of benzene at all residential locations together were observed as 3.1µg/m³.

High concentration of benzene at Burdi (4.5 µg/m³) and Dharampeth (3.7 µg/m³) indicates that the nearby traffic junction and petrol pump has a high impacts on the background concentrations of benzene at these sites. The concentration of benzene at Seminary hills and Gorewada were observed as 2.0 µg/m³ and 1.2 µg/m³. There is an outer ring road with heavy traffic flow, which might be the additional contributors of benzene at these residential sites.

Time Weighted Average (TWA) Threshold Limit values (TLVs) of benzene along with risk levels as given by American Conference of Governmental Industrial Hygienists (ACGIH) and Occupational Safety and Health Administration (OSHA) are given in Table 4. It has been observed that the levels of benzene were well within the ACGIH and OSHA TLVs. As per the National Ambient Air Quality Standards in India, only the annual limit for Benzene was prescribed as 5 µg/m³. The concentration of benzene was exceeding the annual limits at traffic squares and petrol pumps. While, the concentrations of benzene at all the residential locations were well within the National Ambient Air Quality Standard limits.

Table 3 : Mean concentration with Standard Deviation of Benzene at some Residential Area

Sr. No.	Sampling Locations	Benzene (mg/m³)
Sr. No.	Sampling Locations	Minimum	Maximum	Average±Standard Deviation
1.	Burdi	2.9	6.4	4.5±1.3
2.	Dharampeth	1.8	6.1	3.7±1.4
3.	Seminary Hills	0.8	3.2	2.0±0.8
4.	Gorewada	0.6	1.6	1.2±0.4
Mean				3.1

Table 4 : Threshold limits and risk levels of benzene

VOCs

Exposure limits in Air

RFC

RFD

ACGIH-TLV

OSHA-TLV

NAAQS

TWA

ppm

STEL

ppm

TWA

ppm

STEL

ppm

Annual

µg/m³

Benzene

(CAS No.71432)

0.5

2.5

No safe level Group A

Carcinogenic

No safe level Confirmed

Carcinogen effects on humans

TWA : Time weighted average concentration for a normal 8-hour workday or 40- hour workweek to which nearly all workers

may be repeatedly exposed

ACGIH : American Conference of Governmental Industrial Hygienists – www.acgih.org

OSHA : Occupational Safety and Health Administration – www.osha.gov

NAAQS : National Ambient Air Quality Standards

RFC : Provisional Reference Concentration that is likely to be without appreciable risk of deleterious non cancer effects

during a life time

RFD : Provisional Reference close

Group A : Confirmed Carcinogenic effect on humans by all routs of exposure

Conclusions:

The paper reports ambient toxic benzene emission levels at major traffic junctions, petrol filling stations and some residential areas in an urban city of Nagpur, India. The levels of benzene observed at petrol pumps and traffic squares were appreciably high. The mean concentration of benzene at all residential locations was observed as 3.1 µg/m³and is well within the National Ambient Air Quality Standards of 5 µg/m³. The measurement data will stress the need of monitoring benzene at traffic squares and petrol pumps to develop the air pollution control measures and minimize the health impacts of benzene to commuter, nearby residents and workers. Use of CNG, installation of vapor recovery system and use of mask by workers at petrol pumps were urgently needed.

Acknowledgments:

The authors would like to thank Dr. S. R. Wate, Director, NEERI, Nagpur for his constant encouragement in carrying out the above work. Special thanks are due to Mr. A.G. Gavane, Scientist, NEERI, Nagpur for providing instrumental facilities for the analysis of ambient air samples.

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Received on 19.09.2011 Modified on 29.09.2011

Asian J. Research Chem. 4(11): Nov., 2011; Page 1742-1746