ISSN (0970-2083)

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K.M.Oghenejoboh1, A.A. Babatunde1, and C.T. Nwaukwa2

1Department of Chemical and Petroleum Engineering

2Department of Agriculture and Food Engineering, University of Uyo Uyo - Nigeria

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Air analysis were carried out around four oil flowstation flare stacks to ascertain the extent of air pollution resulting from gas flaring in the area. The analysis showed low concentrations of acid forming anions (SOx, H2S, NOx) but high ozone levels in all fields investigated. The acid-like damage to crops experienced by farmers of the host communities were attributed to the combination effect of ozone and sulphur dioxide. The analysis also show high concentrations of carbon monoxide (CO), volatile organic compounds (VOC) and particulate in two of the fields investigated. This was as a result of crude carry-over to the flare due to the low viscosity of the crude from these fields. A correlation showing the effects of viscosity on the production rate of these pollutants was carried out. The correlation showed inverse relationship between the viscosity and the production of these pollutants. The effects of the analysed pollutants in the environment to the economic life and health of the inhabitants of the host communiteis is also discussed


Gas flaring, Air pollutants, Anthropogenic activities, Ecosystem


Air, which constitutes about 80% of man’s daily intake by weight, if polluted may cause profound undesirable effects on human health and other equally negative consequences. Air is said to be polluted when its natural uses are impaired (Schandorf and Asiedu, 2003). The major forms of air pollutant – gaseous and particulate may be classified into primary and secondary pollutants.. Primary pollutants include oxides of sulphur, most oxides of nitrogen and carbon monoxide. These are pollutants directly emitted into the atmosphere from industrial processes. Secondary pollutants on the other hand include ozone and products of photochemical reactions including those formed as a consequence of chemical reactions involving the primary pollutants and other agents such as sunlight (Singh and Prakash, 2003). Since primary pollutants are largely due to human processes, they are referred to as anthropogenic (Cunningham et al. 2005). One of the anthropogenic activities is the flaring of natural gas produced in association with crude petroleum. Nigeria currently flares more than 75% of about 1.78 Billion cubic metres of associated natural gas, which would have been used in generating various forms of energy including electric power. (Oghenejoboh and Akpabio, 2002a; Oghenejoboh and Akpabio, 2002b). This makes her the World’s highest gas flaring Nation. Table 1.1 gives the percentage of gross production of natural gas flared by nine major oil producers of the World.


Table 1: Gas Flaring by major oil producing countries

The products of natural gas flaring emitted into the atmosphere are composed of gases toxic to fauna, flora and human depending on their levels in the atmosphere (Oyekunle, 1999). The combustion products which are made up of the oxides of nitrogen (NOx), sulphur (SOx) and carbon (CO, CO2) may also react with atmospheric water to form acid rain, with its telling negative effects on both human and the ecosystem (Oghenejoboh, 2005). Table 1.2 shows the annual trend of pollutants emitted into the atmosphere from associated gas flaring in Nigeria between 1990 and 1999.


Table 2: Annual Trend of flared gas pollutant 1990-1999

One of the important threat to life arising from gas flaring is the possibility of a rapid warming of the earth due to the accumulation of heat retaining gases on the atmosphere which leads to a phenomenon known as green house effects. This phenomenon (likened to glass in a green house) allows light rays from the sun to pass through but does not allow heat rays generated when sunlight is absorbed by the earth’s surface to escape. An increase in the green house gases (CO2, NO, CH4) in the biosphere causes an increase in the earth’s temperature. An eventual warming of between 1.5°C to 5°C has been predicted from gas flaring in Nigeria (Ilori. 1999). This may lead to gradual melting of the polar ice cap resulting in a global increase of sea level and flooding of coastal areas.

Typical gas flares in Nigerian oil fields are located at ground level and surrounded by thick vegetation, farmlands and huts (20-30 metres from the flare). The heat radiation from the exothermic combustion process is a function of the flame temperature, gas flourides and the geometrical design of the flare stack. In some cases the surrounding soil is scorched, vegetation and farmlands are parched and villagers often complain of internal heat due to the cumulative effects of long exposure to radiant heat (Ilori, 1999, Oghenejoboh, 2005). Emission from very voluminous gas flaring at elevated temperature results in the generation of noise and release of soot and particulate. The noise and elevated temperatures are, however local problems in the immediate environment surroundings of the flares.

In this paper, air analyses around four SPDC flowstation flare stacks were carried out to determine the level of emission of toxic gases from these flares into the atmosphere and to assess the attendant effects of such emission on the health and economic life of the people of the communities where these facilities are located.


The air quality around four Shell Petroleum Development Company (SPDC) Limited’s western operations flowstation flare stack (Afiesere, Utorogu, Evwreni and Eriemu) were analysed for the seven major criteria pollutants. These criteria pollutants (SOx, NOx, COx, H 2S, VOC, O3 and Particulate ) contribute the largest volume of air-quality degradation and also are considered the most serious threat of all air pollutants to human health and welfare. The crude oil produced and processesd at the flowstations under study were also analysed for their physical properties such as density, viscosity and water content.


Air samples were collected, 100 metres (both in the wind direction and against the wind) away from the flare stack of the flowstations under study once a week for four weeks. The samples were collected using absorption filter papers placed on appropriate stands in the sample locations. The absorption papers were left in the fields on the day of experiment for 12 hours (7.00 am to 7.00 pm). At the end of each day the absorption papers were sent to the laboratory for analysis of the criteria pollutants. These experiments were carried out during the dry season months of January and February 2006. This is to avoid the dissolution of the gaseous pollutants by rain water.


The results of the experiments are presented in the Tables.


From the summary of the results presented in Table 2.3 and accompanying percentage comparisons in Figures 1- 4, it could be noticed that the concentrations of the most toxic pollutants (SOx, NOx, VOC) are low when compared with the Department of Petroleum Resources (DPR) tolerance level for these criteria pollutants (FEPA, 1997). However, the ozone concentrations for the four fields studied were relatively high, with Afiesere and Eriemu fields recording concentrations of 150% of the DPR tolerance level, while that of Utorogu and Ewreni were 100%. Ozone as we all know, when in the upper atmosphere (i.e. stratospheric ozone) is a very useful irreplaceable resource that helps to filter out dangerous ultraviolet (UV) rays fom our solar system. Without this shield, life on earth’s surface would be subjected to life threatening radiation burns and genetic damage (Nagashima, 2002). Howeve, at ground level, ozone is a harmful pollutant damaging plants and poses serious danger to humans.


Table 3: Results of crude oil analysis


Figure 1: Percentage comparison of Afiesere field Criteria pollutants with DPRstandards


Figure 2: Percentage comparison of Utorogu field Criteria pollutants with DPRstandards


Figure 3: Percentage comparison of Eriemu field Pollutants with DPR Standards


Figure 4: Percentage comparison of Evwreni field Pollutants with DPR Standards

In the communities around the four oil fields under study, it has been noticed that mottling (discolouration) occurs in the leaves of crops such as cassava, yams, vegetables, okro and other food crops within a few days of cultivation. This phenomenon which is due to chlorosis (bleaching of chlorophyll) eventually kills the whole plant. Since the concentrations of acid producing anions in the air are very low, these symptons are vague and difficult to attribute to acid rain (Oghenejoboh, 2005 ; Adeyinka, 1998). However, research has shown that pollutant levels too low to provide visible symptons of damage can still pose important effects. This is because certain combinations of environmental factors have synergistic effects in which the injury caused by exposure to two factors together is more than the sum of exposure to each factor individually. For instance, when white pine seedlings were exposed to subthreshold concentrations of ozone and sulphur dioxide individually, no visible injury occurs. But when the same concentrations of these pollutants were given together visible damages occurred. (Cunningham et al. 2005). In another field study, using open top chambers and charcoal filtered air, it was discovered that the yield of some sensitive crops, such as soybeans were reduced as much as 50% by the combination of ozone and other photchemical oxidants. (Krupa, 1997). Therefore, the unusual phenomenon currently being experienced by farmers in these communities may not be unconnected with the combination effects of ozone (which concentrations in very high in the atmosphere) and sulphur dioxide.

The results also show very high concentrations of carbon monoxide (CO), volatile organ compounds (VOC) and particulates in the air analysis of Utorogu and Evwreni fields. These high concentrations may be explained by excessive crude carry-over to the flare as a result of the low viscosity of the crude from these fields compared with that from the other two fields as can be seen in table 2.1. The dependence of viscosity on the production rate of CO, VOC and particulate is shown in Figure 5.


Table 4: Results of air sample analysis 100 metres from flare stack


Table 5: Comparison of criteria pollutants in studied area with DPR standards


Figure 5: Effects of crude oil viscosity on the production of carbon monoxide, volatile organic compounds and particulate by associated gas flares

The flares of these two fields are visibly thick, sooty and smoky. The effects of these pollutants in the affected communities are obvious. The inhabitants of these communities complain of excessive heat even in the heart of the raining seasons. The heat, according to the inhabitants had been responsible for poor farm yields as most of their crops wither from the scotching heat. The excessive heat may not be unconnected with the presence of too much atmospheric carbon dioxide from the oxidation of carbon monoxide. Though, carbon dioxide is necessary for plant growth, increased level of it leads to increased environmental temperature or global warming. This excess carbon dioxide in the biosphere can be controlled by keeping the environment green (Attah, 2003). Unfortunately, great quantities of soot particulate from these flares coats the plant leaves thereby reducing photosynthesis. High level of carbon monoxide in the atmosphere also have negative health implications. Carbon monoxide attacks the respiratory, digestive, circulatory and sensory organs (Davies, 1998). This may be responsible for high cases of hypoxia, lungs defects and hypertension induced stroke frequently diagnosed in the cottage hospitals established by the oil producing company in these two communities.


From the experimental results and discusions, it is clear that the oil producing communities in the Niger Delta are daily exposed to environmental pollution resulting from oil production activities especially gas flaring. The inhabitants who are predominantly farmers and fishermen have invariably lost their means of livelihood to air pollution. Other studies carried out by other authors had shown that the health effects of continuous pollution arising from oil production cannot be quantified (Onwioduokit 1999, Akpofure et al. 2000).

It is true that the Federal Government of Nigeria has, at various times enacted laws to protect the environment. Such laws in most cases are not enforced. This provocative attitude of the government has been instrumental to the high youth restiveness in the Niger Delta region. Many a times, this had resulted to vandalisation of oil installations with attendant demand for financial compensation. Vandalisation, instead, of solving problems of environmental degradation, agravates it. No matter how much money is paid in the interim as compesation, the fact remains, that there is no such thing as oil pollution restoration, because a broken ecosystem cannot be fixed as does a broken bone.

It is heartwarming, however, that by the time the no-flare policy of the Government comes into effect in the year 2008, the inhabitants of the oil producing communities will heave a sigh of relief.


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