Energy Sources, Part A, 31:223–231, 2009

Copyright © Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/15567030701399479

Air-borne SO2 Pollution Monitoring

in the Upstream Petroleum Operation Areas

of Niger-Delta, Nigeria

E. O. OBANIJESU,1 F. M. ADEBIYI,2 J. A. SONIBARE,3 and

O. A. OKELANA1

1Chemical Engineering Department, Ladoke Akintola University of

Technology, Ogbomoso, Nigeria2Environmental Pollution Research Laboratory, Department of Chemistry,

Obafemi Awolowo University, Ile-Ife, Nigeria3Environmental Engineering Research Laboratory, Chemical Engineering

Department, Obafemi Awolowo University, Ile-Ife, Nigeria

Abstract In the process of crude oil production, sulfur dioxide (SO2) gas is producedas a result of flaring and booming of crude oil associated gases. This paper presents

the study carried out on the monitoring of SO2 emission from some oilfields inthe crude oil producing areas of Niger-Delta region of Nigeria. Six locations were

studied while monitoring involved morning and evening times for four months usinga Testo 350 Flue Gas Analyzer. Comparison of the mean measurements with Nigerian

FEPA tolerance limits indicate that SO2 values from 60 m away from the point sourcesfor all the fields were comparatively higher than their maximum tolerance limits of

50 �g/m3 for long term exposure and SO2 values were also comparatively higherthan the emission limit range (30–300 �g/m3) for SO2 from stationary sources. It is

concluded that this breach of tolerance level may result in acid rain formation, whichcan be detrimental to the environment while the long-term effect can alter the ecology

of the areas. It is recommended that the environmental matrix quality for soil, water,and air be carried out for these areas periodically.

Keywords gas analyzer, oil field, pollution monitoring, SO2

Introduction

The release of gaseous emissions arising from the flaring and booming of associated

gas into the environment is common during upstream petroleum operations in the Niger-

Delta region of Nigeria. Problems associated with this practice appear to be growing

in the region owing to the increase in crude oil production. During gas flaring, SO2

is produced as a primary air pollutant. The SO2 undergoes oxidation to produce sulfur

trioxide (SO3), which is further transformed into a dry or moist sulfuric acid (H2SO4), a

secondary air pollutant, through contact with atmospheric vapor. This pollutant may be

transported in the atmosphere over distances of hundreds to thousands of kilometers and

deposited wet or dry. The wet deposition is known as acid rain with pH normally below

Address correspondence to Emmanuel Ogo-Oluwa Obanijesu, Department of Chemical Engi-neering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria. E-mail: emmanuel257@yahoo.com

223

224 E. O. Obanijesu et al.

5.6 (Environment Canada, 2005) while the dry deposition takes place when the sulfate

and gas particles are deposited on, or absorbed onto surfaces. This acid rain goes into

the soil and is taken up by the animals or growing plants in the areas and can alter the

ecology of the areas.

SO2, though not detectable by odor, its adverse effects on health, vegetation, and

buildings can be readily observed (Palmer, 1974). It causes damage to vegetation, animals,

and properties and causes ill health to humans. Through a series of complex chemical

reactions, SO2 emitted by natural gas flares are converted to acids, which may result

in acidity of rain. Photochemical processes, because of their production of radicals, are

strongly coupled to SO2 to form H2SO4 (Song et al., 2003):

SO2 C OH�! HOSO�

2

HOSO�

2 C O2 ! HO�

2 C SO3

HO�

2 C NO ! NO2 C OH�

SO3 C H2O ! H2SO4

(1)

According to Guendel et al. (1994), the reaction usually involves several atmospheric

reactions, which may include those heterogeneous reactions taking place within fog as:

2SO2 C O2 C Catalyst ! 2SO3

SO3 C H2O ! H2SO4

(2)

The catalyst in Eq. (2) above may be ammonia and when this is the case, an acidic

component of the atmosphere may be produced in the conversion process (Renard et al.,

2004); this is usually rapid. In the atmosphere, SO2 and SO3 dissolve in the available

water vapor to form H2SO3 and H2SO4, respectively. These acids are highly corrosive in

nature and come back to the earth as acid rain. Acid rain having pH of about 2.6 destroys

vegetation, lakes, rivers, and rooftops, among others.

Flaring is a common method of disposal of flammable waste gases in the upstream

oil, downstream refining, and chemical processing industries (Akeredolu and Sonibare,

2004); it is an open-air flame usually at the tip of a long stack. The flame is exposed to

the weather elements, particularly winds (Ritter et al., 2002). Gas flares are chosen as the

choice disposal option for handling waste hydrocarbon gases because of their ability to

burn efficiently (Strosher, 1996). Though emission species can be reduced with complete

combustion within available short residence time making flame temperature a primary

variable in the combustion process (Roe et al., 1998), Sonibare and Akeredolu (2004)

identified SO2 as one of these species left if sour gas is involved in combustion.

Gaseous emission monitoring study is part of environmental performance monitor-

ing of production operations aimed at achieving continuous performance improvement

with the ultimate goal of minimizing negative impacts on the environment arising from

production operations. In recognition of the problems this primary air pollutant could

create, different studies are being carried out globally in order to predict and control its

impact on environment. With technological advancements, the vast amount of data about

ambient air is generated to know the quality of air in the environment and administer the

appropriate corrective actions wherever necessary. This study was carried out to predict

the impact of SO2 emissions on air quality in some upstream petroleum operations area

of Nigeria.

Airborne SO2 from Some Oilfields in Niger-Delta 225

For example, in Canada, regulatory approaches on sulfur emissions from Alberta

petroleum production and processing operations address both environmental protection

in the form of ambient air quality guidelines and pollution protection through sulfur

recovery and flaring guidelines (Brian, 2005). Similarly, in the UK SO2 released into the

environment through power stations (combustion processes) led to widespread acidifica-

tion of freshwaters in the uplands since 1850; in recognition of this primary air pollutant’s

contribution to UK and European countries air sheds, the UK agreed in the Gothenburg

Protocol in 1999 to reduce the annual emission of SO2 (expressed as the element S)

to 625 kt-S. This and earlier decisions has led to the drastic declination of annual UK

emission of SO2 which peaked in 1970 at 3,259 kt-S and decreased to 594 kt-S by 1999

and further reduced by 80% by 2001 with a projection of further declination by 2010 in

commitments within the international protocols (NEGTAP, 2001). This reduction in the

SO2 concentration in the UK over the last three decades has virtually eliminated direct

effects on vegetation, leading to an expansion of some lichen species.

Methodology

Six flow stations located at Niger-Delta region of Nigeria were studied for this work

(Figure 1). The first site (Oilfield 1) was located in a swamp and saltwater region of the

Niger-Delta and was mounted on a concrete barge capable of producing about 45,000 bpd

and designed to be unmanned. It has a provision for accommodation with a houseboat as

a support. It operates on electronic instrumentation, electric drive, and a massive power

generation that serves both the facility and the community. The second station (Oilfield 2)

was a sand-filled three-process train facility with production capacity of 135 Mb/d. The

third field (Oilfield 3) is a double bank station with a design capacity of about 80,000

bbl/d. It consists of a flow station, an offshore development platform, and 17 clusters,

unmanned, fully automatic, and fail-safe. The operations crew visits the station on a

daily basis from a terminal logistic base. Oilfield 4 was a 30,000 bpd flow station which

Figure 1. Niger-Delta: Rivers, states and vegetations. (Source: Waado, 2005.)

226 E. O. Obanijesu et al.

Figure 2. Testo 350 portable emission analyzer.

supplies stabilized crude along with produced water to a terminal about 3 km away via

a 12 delivery line. The fifth site (Oilfield 5), which is a swamp piled, three-bank flow

station with each having 45 Mb/d capacities. The station is supported on a piled structure

with a single deck, and built on a piled area of about 50 m by 100 m. Oilfield 6 covers

about 16 km2 and is located at about 65 km southwest in the swamp and salt-water

region of Warri. The field has 17 hydrocarbon bearing reservoirs and presently about 21

producing wells are tied into the station.

A Testo 350 Flue Gas Analyzer (Testo AG, Hampshire, UK) (Figure 2) was used to

measure the SO2 emissions in and around these stations. This analyzer has a detection

limit of 0–5,000 ppm with 1 ppm resolution and a response time of 30 seconds. A

combined wind vane and digital anemometer (Taylor wind scope, Taylor Precision Instru-

ments, Oak Brook, IL, USA) was used to determine wind direction and speed. Sampling

was carried out at 60 m, 200 m, and 500 m from each point source. Measurements were

taken in the morning between 8:00 am and 11:59 am when activities were going on

within the facilities and at afternoon between 4:00 pm and 5:00 pm when the staff was

supposed to be resting.

Air sample was continuously extracted from the atmosphere and a portion of the

sample sent to the analyzer to determine the pollutant of interest. The control unit, which

is a portable measuring instrument for spot checks and measurements on site, is equipped

with a probe socket and an integrated differential pressure probe. The comprehensive

range of probes makes it possible for accurate measurements of temperature, pressure,

humidity, velocity, current, and voltage.

Results and Discussion

The results of the SO2 measurements at the six oilfields are presented in Tables 1–6 with

the summary in Figure 3. At point source distance 60 m, Oilfield 1 with a mean value

of 472 �g/m3 has the highest SO2 concentrations followed by Oilfield 2 with a mean

Airborne SO2 from Some Oilfields in Niger-Delta 227

Table 1

Daily SO2 concentrations for Oilfield 1 (�g/m3)

Point source distance, m

Week 60 200 500

1 400 120 90

2 390 110 85

3 600 400 120

4 610 309 125

5 350 100 90

6 330 90 93

7 400 120 90

8 390 100 93

9 300 180 115

10 310 188 110

11 500 125 125

12 490 120 130

13 750 180 115

14 730 170 110

15 500 125 125

16 500 120 125

Mean 472 160 108

Table 2

Daily SO2 concentrations for Oilfield 2 (�g/m3)

Point source distance, m

Week 60 200 500

1 350 290 160

2 340 300 150

3 210 250 250

4 200 255 250

5 750 180 115

6 750 175 110

7 500 125 125

8 510 120 125

9 750 180 115

10 700 180 110

11 400 125 125

12 420 110 130

13 600 180 115

14 590 170 110

15 500 125 125

16 500 120 125

Mean 462 180 140

228 E. O. Obanijesu et al.

Table 3

Daily SO2 concentrations for Oilfield 3 (�g/m3)

Point source distance, m

Week 60 200 500

1 750 180 115

2 740 180 110

3 500 125 125

4 490 120 125

5 80 65 50

6 80 66 52

7 100 80 60

8 80 75 57

9 120 90 71

10 135 100 100

11 135 100 100

12 125 94 89

13 700 170 110

14 700 160 100

15 500 115 120

16 500 110 120

Mean 353 114 94

Table 4

Daily SO2 concentrations for Oilfield 4 (�g/m3)

Point source distance, m

Week 60 200 500

1 650 315 185

2 650 320 180

3 710 350 200

4 700 340 190

5 100 685 150

6 90 680 155

7 145 100 80

8 140 90 79

9 150 890 160

10 145 880 165

11 160 120 180

12 150 110 190

13 620 305 180

14 620 300 170

15 700 330 210

16 700 320 200

Mean 402 383 167

Airborne SO2 from Some Oilfields in Niger-Delta 229

Table 5

Daily SO2 concentrations for Oilfield 5 (�g/m3)

Point source distance, m

Week 60 200 500

1 200 65 60

2 200 60 59

3 250 80 70

4 240 86 77

5 60 70 100

6 59 66 90

7 75 80 150

8 70 75 130

9 300 125 80

10 300 120 71

11 455 135 90

12 450 120 89

13 210 64 60.5

14 200 63 59

15 260 80.5 71

16 250 84 73

Mean 224 86 83

Table 6

Daily SO2 concentrations for Oilfield 6 (�g/m3)

Point source distance, m

Week 60 200 500

1 300 315 60

2 300 310 60

3 1,125 120 75

4 1,100 120 77

5 250 280 200

6 220 280 200

7 300 450 200

8 290 440 190

9 70 150 600

10 70 140 590

11 80 200 100

12 70 190 950

13 310 320 60

14 300 310 70

15 1,120 120 74

16 1,100 125 73

Mean 438 242 224

230 E. O. Obanijesu et al.

Figure 3. Average SO2 measured concentrations in and around the studied areas.

value of 462 �g/m3. At point source distance 200 m, Oilfield 4 with a mean value of

383 �g/m3 has the highest SO2 concentrations followed by Oilfield 6 with a mean value

of 242 �g/m3. Likewise, at point source distance 500 m, Oilfield 6 with a mean value of

224 �g/m3 has the highest SO2 concentrations followed by Oilfield 4 with a mean value

of 167 �g/m3 while Oilfield 5 has the lowest mean values of SO2 at each of the point

source distances. As may be expected, the highest concentrations of SO2 were obtained

at point source distance 60 m (the closest point to the sources) with a mean value of

393 �g/m3 and a range of 224–472 �g/m3. This is about twice the mean concentrations

at distance 200 m and thrice that of the distance 500 m away from the sources.

Comparison of the mean measurements (Figure 3) with Nigerian FEPA (1991)

tolerance limits indicate that SO2 values from 60 m away from the point sources for all

the fields were comparatively higher than their maximum tolerance limits of 50 �g/m3 for

long-term exposure. At point source distances 200 m and 500 m, the SO2 concentrations,

though very high, fall within the limits of SO2 emissions from the stationary sources. The

comparatively high concentration of SO2 pollutant at these sites may result in acid rain

in the studied areas and this could partly be responsible for the acid rain once reported

in the Niger Delta area of the country (NDES, 1997).

Conclusion and Recommendation

The SO2 measurement data interpretation from these oil fields indicates that the produc-

tion of the crude oil could pose considerable environmental hazards. If, in the process

of production and refining of the crude oil, the effluent are not well managed before

discharge or there is still continuous flaring and booming of gases, the environment can

be polluted. As a result of large quantities of SO2 that are fared and boomed, there

may be a need to recover these gases for commercial use. Processes such as flue gas

desulphurization, tall stacks, wet scrubbing, and adsorption could be applied to control

the air-borne SO2 pollution. It is recommended that the environmental matrixes (soil,

water, and air) qualities of these areas be done periodically as in the case of other oil

producing regions of the developed nations.

Airborne SO2 from Some Oilfields in Niger-Delta 231

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