


































Energy and Earth Science 
Vol. 7, No. 2, 2024 

www.scholink.org/ojs/index.php/ees 

ISSN 2578-1359 (Print)   ISSN 2578-1367 (Online) 

 

1 

 

Original Paper 

Flare Pollution Loads and Carbon-Dioxide Effect on Rainwater 

Acidity in Niger-Delta: A Review, Investigation and Model for 

Safe Living Quarter 

Ugwunna D. Amadi
1*

 & Godpower C. Enyi
1
 

1
 Department of Petroleum and Gas, University of Salford, M4 5WT, United Kingdom 

*
 Ugwunna D. Amadi, Department of Petroleum and Gas, University of Salford, M4 5WT, United 

Kingdom 

 

Received: July 7, 2024         Accepted: July 18, 2024       Online Published: August 12, 2024 

doi:10.22158/ees.v7n2p1                  URL: http://dx.doi.org/10.22158/ees.v7n2p1 

 

Abstract 

Carbon-dioxide does not only affect climate change, but also contribute tremendously in acidification 

of rain water. Hazard identification and risk assessment are fundamental components of effective risk 

management, specifically in sensitive areas where adverse effects can have significant consequences. 

This study provides novel methodology for environmental and safety assessment of flared gases in 

sensitive areas such as residential homes. Distancing Sampling Technique (DST) was used to 

investigate the sensitivity of rain water pH at distances away from flare site in order to develop a Risk 

Management Model for sensitive regions. First, a review on rain water acidity was made around 

flaring and non-flaring areas in Niger-Delta states, which revealed Moderate-High acidity effect 

around flaring zones and no effect on non-flaring zone. Secondly, Flared Gas Quantification, pH 

Experimental Evaluation (PEE) and Risk Assessment Matrix (RAM) were the three systematic 

approaches used respectively to quantify, measure and evaluate the effects of CO2 and other flare 

pollutants around the area of study. An average of 809,300,000 Mscf of associated petroleum gases 

were flared around the oil and gas producing areas in Delta State, causing a release of around 43x10
6 

tons of CO2 from 2012-2022. Experimental results showed the range of pH from 4.56 ± 0.06 to 5.10 ± 

0.06 for the 33 samples of harvested rainwater in Kwale community, Delta state causing a deviation of 

16.38 to 30.05% from standard. The developed and validated model suggests 4.81KM radius as the safe 

distance for human habitation from flare sites. Based on these findings, carbon-capture and 

sequestration projects must be activated in Niger-Delta to curb the menace.  



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Keywords 

Acid rain, Distance sampling, Standard Deviation, Risk Matrix, CO2 sequestration 

 

1. Introduction 

The need to address risk issues in a continuously evolving environment, coupled with improved 

information and communication technologies has led to the development of several techniques, hazard 

identification and risk assessment methods (Villa & Cozzani, 2015). Risk analysis by dynamic 

approach have been an evolving method for identifying, assessing, and quantifying increasing risk in a 

system with uncertainty, real-time changing environment, and system complexity (Bucelli, et al., 2018; 

Villa & Cozzani, 2015). 

A systematic approach for defining safe residential quarters due to pollution by flared gases around 

flare regions are still lacking. Nduka, J. et al. (2008), collected rainwater samples from Portharcourt 

and Warri, which are two major oil and gas industrial areas in Niger-Delta, to determine the water pH, 

while control samples were collected from Awka in Anambra state, which was non-oil and gas hub. 

The samples were collected up to 115m from a reference point in a triangular equilibrium using clean 

plastic basins. The pH readings are as follows: Portharcourt (4.71,4.94,4.93); (5.04,5.73,4.91): Warri 

(4.81,4.70,6.15);(4.79,4.80,4.72): Awka (6.04,5.88,5.75); (6.00,5.10,5.96). The pH of rainwater in 

Portharcourt and Warri, were highly acidic due to industrial activities (gas flaring) while the pH of 

Awka acting as control is within acceptable range.  

Odjugo, P. & Osemwenkhae, E. (2009), determined the effects of gas flaring on crops grown in 

Niger-Delta. The results of their work reveals that the flare affects extends beyond 110 meters from the 

flare location and therefore advised on further studies to validate the claim. Atuma, M. I., & Ojeh, V. 

(2013), examined the effect of flared gases on soil and casava productivity from five sites in Ebedei, 

Ukwani LGA of Delta State in Niger-Delta. The soil samples were harvested at varying depths and 

distances ranging from 0 - 20cm and 50m - 250m respectively from the bund wall of the flares. Critical 

analysis using multiple regression and paired t-test methods shows wide acidity variation in the results 

obtained in flaring area to those from the controlled site (non-flaring area). However, the researchers 

did not attempt to model a safe threshold for human habitation in those areas due to adverse effects of 

rain acidity. 

In this research, Environmental assessment of risk of CO2 and other flare pollutants was investigated by 

evaluating the pH of rainwater around Delta state, a region in Niger-Delta, which was conducted 2KM 

from flare sites for two consecutive years. The study was aimed at providing simple methodology for 

safety and environmental assessment of flared gases in sensitive areas at defined distances from flare 

sites followed by measuring the pH of the water and modelling safe human quarters. pH is an 

incredible parameter that plays a key role in assessing water quality. In environmental sampling and 

monitoring, the pH value indicates the pollution index of the water, which has potential adverse effect 



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on the environment, people and ecosystem. On the light of the above, the present work on impact 

assessment focuses more on the influence of flared gases on rainwater acidity at specific intervals up to 

2KM. 

Niger-Delta region of Nigeria has proven natural gas reserves of 203.16 Trillion Cubic Feet (TCF) and 

crude oil reserves of 36.89 billion barrels (bb) and between 400 TCF-600 TCF of undiscoverable 

natural gas reserves. This is estimated to be within 7.7% -15.5% of global quantity of undiscoverable 

natural gas resources. Judging by the trend, some considerable amount of the associated gases when 

produced would be flared leading to huge economic loss and consistently endangering human health, 

ecosystem and general environment.  

Acid rain and most environmental pollutant have been widely attributed to impact of gas flaring 

especially in the Niger Delta region of Nigeria (Elijah 2022; Ebong, et al., 2022; Nwankwo & 

Ogagarue, 2011). Gas flaring does not only affect climate change but also pollutes the environment, 

with utmost effect to inhabitant in close proximity to flare sites. Hazard identification, risk assessment 

and mitigation plan are keys for prevention of chances of diseases, calamities and mishaps in sensitive 

areas. 

 

2. Review of Literature 

Rainwater is water fallen as rain that has not collected soluble matter from the soil and is therefore soft. 

It is also a surface water obtained from rain fall, which is an excellent source of domestic water for 

rural areas and dispersed population (Anyata, 2008; Odume, 2022). Water is essential for the 

environment, human health, food security and sustainable development, whose quality is an 

indispensable requirement for healthy living (Schiller, 1982; Adeyeye, et al., 2019). It becomes a 

problem to humanity, ecosystem and the environment when the physical and chemical balances of the 

water chemistry are altered due to natural or anthropogenic activities.  

Acid rain is a normal rain acidified by certain air pollutants. Rain water acidification is a serious 

environmental problem of trans-boundary nature caused by the oxides of sulfur and nitrogen and 

worsened by increasing amount of carbon-dioxide in the atmosphere (Singh & Agrawal, 2007). 

Whereas the normal rain cleanses, supports, enriches life and the environment, acid rain dirties and 

damages life, ecosystem and the environment (Abbasi, et al., 2013). Acid rain is considered by many as 

one of the grave environmental threat of our time caused by air pollution that have led to fish extinction 

and forest dieback (Grennfelt et al., 2020).  

Acidic rain poisons our water bodies and lowers the soil pH. Lowered soil pH leaches away nutrients 

cations and increases the exposure of heavy toxic metals, which reduces soil chemical properties that 

enhances soil fertility. When the soil chemistry is compromised, it impacts negatively on growth and 

productivity of plants and forest trees. Basically, the degree of acidity of water and soil is measured by 

pH, which is a shorthand version of potential hydrogen. Figure 1 displays the origin of pollutants that 



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acidifies rain water, cause climate change and other environmental threats. 

 

 

Figure 1. Cause and Effect Diagram for Environmental Pollutants Which Acidifies Rain Water 

 

2.1 Gas Flaring Proximity to Residential Areas 

In Niger-Delta, there are widespread perceptions that due to human habitation in close proximity to 

flare locations, it has adversely affected the region in terms of human health status, environmental 

degradation, and social-economic issues (Nriagu et al., 2016; Otache et al., 2021). This is due to daily 

released amount of the dangerous toxins into the atmosphere, resulting to the pollution of air, water, 

soil and the ecosystem (Oghenejoboh et al., 2007). 

The impact of gas flaring spreads across extensive radius from the point of generation. In Niger-Delta 

at least Two Million (2,000,000) people lives within Four Kilometres (4KM) (2.5 miles) in flaring 

locations (NOAA Virtual Night Flare, 2018). 

 

 

Figure 2. Yellow Spots Showing Population of Residential Homes at less than 2KM from Flare 

Sites in Niger-Delta 

Source: Global Gas Flaring Tracker Report, July, 2020; https://gasflaretracker.ng/ 

 



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These emissions have caused series of litigation from the host communities to the oil and gas company, 

government agencies, resulting to claims and counter claims (Nduka et al., 2008). Flaring as a major 

source of greenhouse gases generates noise and heat leading to health issues and environmental 

degradation (Emam, 2015; CAPP 2012; Abiodun, 2014; Oseji, 2007; Ejiogu et al., 2019). Scientific 

studies have identified over 250 toxins released from flaring. They include carcinogens such as 

benzopyrene, benzene, carbon-disulphide (CS2), carbonyl-sulphide (COS) and toluene. Others are 

metals such as mercury, arsenic and chromium, sour gas with H2S and SO2, nitrogen oxides (NOx), 

carbon-dioxide (CO2), methane (CH4) etc which contributes to greenhouse gases (EPA 2014; 

Christiansen et al., 2016; Mobolaji Sunmoni, 2018).  

2.2 Specific Effects of Acid Rain 

Specifically, acid rain affects human health, damages the soil, plants, trees as wells as buildings and 

structures (Singh & Agrawal, 2007; Abbasi et al., 2013). Acid rain not only damages the chemistry of 

soil but also changes the quality of soil (Fiza Fatima et al., 2021). It distorts the enzymes of microbes in 

the soil, kills them, leaches the soil essential nutrients, decreases soil fertility and causes stunted growth 

of plants (Singh & Agrawal, 2007; Atuma & Ojeh, 2013). 

Acid rain washes heavy metal toxins like Magnesium (Mn), Aluminium (Al), Lead (Pb), Iron (fe), 

Mercury (Hg) and gets them dissolved in the soil, which permeates down to the ground drinking water 

and poisons it. While some of these toxins are washed off and flows to the rivers, lakes and streams 

(Nwankwo & Ogagarue, 2011; Ejiogu et al., 2019; Ebong et al., 2022). The accumulated heavy metals 

in human bodies through ingestion of the poisoned water, causes headache, irritation of throat and nose, 

coughs etc. Excess ingestion of these toxins contributes to kidney and heart issues, lung diseases such 

as Asthma, bronchial problems, etc.  

Direct exposure of human body to acidified liquids affects the immune system, which drastically 

reduces human antibodies (Nagae et al., 2011). The direct droplet of acidic rain water lowers the pH of 

the water bodies therefore adversely affects the living things in the water. Accumulation of heavy 

metals in the water bodies affects the breaths of fishes leading to premature deaths. The above 

phenomenon equally affects the food chain at different levels. When humans eat these poisoned fishes, 

the heavy metals will be deposited into the human body, also when animals or birds eat the dead fishes; 

they also become a secondary receiver of the poisoned food. 

2.3 Chemistry of CO2 Release from Combustion Process 

Flared gases are composed of various forms of gases (methane, ethane, propane, butane, pentane, 

hexane, etc.), water vapour, hydrogen sulphide, nitrogen, volatile organic matters, etc. (Peterson, 2007; 

Putriastuti, et al., 2021). During gas flaring, the combusted gases generate mainly Carbon-dioxide 

(CO2), water vapor and heat (Gzar & Kseer, 2009). This is evident in equations (2.1-2.5).          

 

 



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The presence of CO2 in the atmosphere causes acidity of rain water according to the chemical reactions 

blow. 

   

 

In equation (2.6), carbon dioxide (CO2) reacts with rainwater (H2O) to form carbonic acid. The 

presence of hydrogen ion molecules “H
+”

 in the water renders it acidic by lowering the pH as shown in 

equation (2.7). Accumulation of H
+
 due to higher concentration of CO2 from combustion process 

further acidifies the rain water. 

 

3. Materials and Methods 

In this research, a field work around a flare location in a community in Kwale area of Delta state was 

carried out. The sole purpose was to measure the pH of rain water harvested in the format describe in 

Figure 3 and in three stages as described in Figures 4, 5 & 6. A measurement tape, machete, labeled 

white plastic bowls, labeled retrieval bottles, Beaker and a digital pH meter were the key apparatus 

used for the field sampling and experimental evaluation.  

 



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Figure 3. Model for Rain Water 

Sampling Points: F=Farm Area; R=Residential Area;  

X1,X2,X3=Sampling Axis with Sampling Points. 

 

3.1 Research Method 

The sampling stages and experimental scenarios follow the sequence defined in Figures 4, 5 & 6 of this 

report. 

3.1.1 Stage 1: Chart for Rain Water Harvesting and pH Experimentation along Axis X1 

Total of thirty three (33) rain water samples were harvest from axis X1, X2, X3 for the three (3) stages 

of field work as describe below. Figure 4 is the first stage done which involves sampling points 

clearing, positioning of bowl for rainwater collection and pH experimentation. Four points cleared in 

Day 1, seven points in Day 2 while the bowls were positioned on the eleven cleared points in Day 3, 

followed by pH evaluation in Day 4.  

 

 

 

 

 

 

 

 

 

Figure 4. Sampling and pH Evaluation Timeline along X1 Axis 

 

 



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Stage 2: Chart for Rain water harvesting and pH experimentation along Axis X2 

Figures 5 & 6 is the second stage of the sampling and experimentation process along axis X2 and 

X3.The process includes sampling points clearing, bowls positioning and pH evaluation in the 

laboratory for the harvested water samples. 

 

 

 

 

 

 

 

 

Figure 5. Sampling and pH Evaluation Timeline along X2 Axis 

 

Stage 3: Chart for Rain water harvesting and pH experimentation along Axis X3 

Figures 3 & 4, is the last stage of the sampling and experimentation process along axis X3 done in the 

third year of this research. The process is in similar fashion with stages X1 and X2. 

 

 

Figure 6. Sampling and pH Evaluation Timeline along X2 axis 

 

Where;  

X1, X2, X3=Axis of measurement   

P1, P2, P3 … P11=Sampling points;  

B1, B2, B3 … B11=Sampling Bowls 

pH.S1, pH.S2, pH.S3…….pH.S11=Evaluated pH of each retrieved water samples 

 

 



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3.1.2 Assessment of Flared Gases and CO2 in Niger-Delta Using Quantification Approach 

The amount of flared gases and emitted CO2 over 11 years (2012-2022) as monitored by Nigeria Gas 

Flare Tracker, an online software was use to quantify the volume of flared gases (MSCF) released on 

daily basis in Niger-Delta states and its environ. Earth Observation Group (EOG) at the Colorado 

School of mines in 2011 developed this satellite software that tracts and records flaring data with 

locations, temperature, source, sizes and radiant heats from infrared emitters worldwide.  

In Nigeria, this software is monitored via (https://gasflaretracker.ng) and managed by National Oil Spill 

Detection and Response Agency (NOSDRA). Table 1 displays volume of flared gas vis-a-vis the 

amount of CO2 respectively emitted in Edo, Delta, Rivers, Bayelsa, Akwa-Ibom, Imo and Abia state. 

These are the states that comprise Niger-Delta. 

 

Table 1. 11 Years Profile of Emitted Carbon-dioxide (x10
3
 Tonnes) from Flared Gases (x10

3
 

MSCF) in Niger-Delta States 

Yr. 

EDO DELTA RIVERS BAYELSA 

AKWAI-IBO

M IMO ABIA 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

F.Gas 

x103 

E.CO2 

x103 

2012 12200 648.9 49000 2600 55400 2900 30400 1600 3700 197.3 15100 800.1 45.9 2.4 

2013 19100 1000 67600 3600 57500 3100 34500 1800 6800 359.9 16400 869.5 1300 71.3 

2014 21200 1100 62200 3300 68100 3600 36200 1900 5500 294.1 9400 500 1000 54.1 

2015 21600 1100 65900 3500 56800 3000 26500 1400 6100 322.2 7500 397.9 458.8 24.4 

2016 9900 527.6 52400 2800 68000 3600 37000 2000 5700 304.8 8400 444.5 132.9 7.1 

2017 14100 746.9 69600 3700 70000 3700 36200 1900 6000 316.8 7600 404.9 451 24 

2018 24800 1300 113200 6000 65700 3500 45500 2400 5900 312.7 6600 353.8 1200 64.5 

2019 24800 1300 105200 5600 68900 3700 47000 2500 4600 246.5 8200 435.2 1100 56.8 

2020 17800 947.8 99700 5300 57900 3100 42400 2300 3100 164.8 10300 545 603.1 32 

2021 16900 897.8 66300 3500 38600 2100 23500 1200 2500 130.3 6900 366.3 385.5 20.5 

2022 12900 684.1 58200 3100 31800 1700 18100 1000 2500 130.9 4600 241.8 0 0 

Note. Where: F.Gas=Flared Gas; E.CO2=Emitted CO2. 

 

3.1.3 Experimental Procedure 

Thirty three (33) samples were collected at intervals of 200 meters (0.2KM) from the bunk wall of a 

typical flare site to a distance of 2KM along axis X1, X2 and X3. The task includes clearing of 

sampling points, positioning of water collection bowl and laboratory investigation.  

Upon retrieval of the harvested rain water in labeled receptacles, standard quantity of 100ml of the 

sample was measured and poured into a calibrated beaker, and the digital pH meter was switched ON 



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for 30 minutes to warm up, next was calibration of the unit in a buffer solution. The sample was stirred 

for 2 minutes, the electrode rinsed, the meter set in pH mode and the electrode inserted into the beaker 

followed by activating the pH measurement button. A stable pH reading was achieved within 60 

seconds. After each reading the electrode was rinsed with distilled water and second and third reading 

done on same sample for result comparison. By implication, all harvested rain waters were tested thrice 

for data validation using same procedure.  

3.1.4 Rain Water pH Analytical Procedure 

The evaluated pH data was analyzed by Risk Matrix Approach using percentage standard deviation 

method. Risk is a function of probability of occurrence of an undesired event in addition with a 

measure of its adverse consequence. The procedure involves identification of the hazards, 

quantification of likelihood and consequence of those hazards on health and environment. Standard 

deviation is a measure of amount of dispersion or variation from the data set. It specifically gives a clue 

on how far each value lies from the average or mean. A high standard deviation indicates that the 

values are far from the mean and vise verse. This approach was used in this research to analyze the rain 

water pH along X1, X2 and X3 axis and compared with the standard mean (ẍ) value of 5.6.  

The Standard Percentage Deviation (SPD) for the harvested rain water pH data was computed in Excel 

spreadsheet using equation (3.1). 

   

Presented in Table 2 and 3 are the Flared Gas Risk Assessment Matrix and Risk Factor respectively 

employed as tools for the Risk Evaluator based on the magnitude of the flare pollutants effects on the 

people, community or environment. The Risk Factor (R.F) is a product of probability of occurrence 

(Likelihood) and severity. Mathematically,  

 

Where; 

;  

 

 

 

 

 

 

 

 

 

 



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Table 2. Risk Assessment Matrix 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

               

 

 



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Table 3. Risk Factor 

 

 

 

 

 

 

 

 

 

 

 

3.1.5 Impact Rating and Description 

Negligible-Low Risk Zone (NLRZ): It is characterized with negligible effects from flaring activities but 

mitigation measures may be desirable. The flare impact may not result to significant effects on the 

people, community or environment even if ignored. 

Low-Medium Risk Zone (LMRZ): It is characterized with significant impact, requiring mitigation to 

curb the effects. The flare impacts may results to negative Short-to-Medium Term effects on the people, 

community or environment. 

Medium-High Risk Zone (MHRZ): It is characterized with serious impact requiring immediate 

mitigation plan to drastically curb the menace. The flare impacts may result to a Medium-to-Long 

Term effects on the people, community or environment. 

High-Critical Risk Zone (HCRZ): It is characterized with severe impact on the people, community and 

the environment if adequate steps are not employed to stem it. The flare impact may have already 

resulted to a Long Term adverse effect on the people, community or environment around that zone. 

Critical-Intolerable Risk Zone (CIRZ): It is characterized with very severe impact on the people, 

community and environment. These effects are usually immitigable if the practice continues. The only 

panacea is to stop the practice generating the effects. 

3.2 Model for Determining Safe Habitation Quarter in Sensitive Areas 

In order to predict the safe human habitation zone from flare locations, R-Squared was used to study 

the variance of the independent variable (Distance) to the dependent variable (pH), using the mean 

regression equation. R-Squared is a coefficient of determination in statistical regression model for 

evaluating the proportion of variance of the variables (dependent from independent) which defines the 

goodness of fit from their relationship. Based on the generated R-Squared value, which is more than 

80% for the mean pH as shown in figure (12), a regression model was developed. 

The regression equation along the path of investigation is defined by: 



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=  

=  

By Gaussian elimination Method 

=  

 

 

 

 

3.3 Risk Evaluation Model 

Generic Risk Model at varied distance, xi  

 

 

 

 

4. Results and Discussion  

This research was done by quantifying the amount of released carbon-dioxide vis-à-vis emitted flared 

gases for 11 years in seven states of Niger-Delta. This is followed by determination and analyzation of 

the pH value of 33 samples collected at 200 meters interval and finally evaluating the safe zone for 

human habitation from flare locations. All data were calculated via Excel worksheet, graphical figures 

developed analyzed using Origin 2023(10.0) software. 

 



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Figure 7. Emitted Flared Gas Profile for 11 Years in Niger-Delta State 

 

4.1 Volume of Emitted Gases Vis-a-vis of CO2 Released for 10 Years in Niger-Delta States 

 

 

Figure 8. Area Profile of Emitted CO2 per State in Niger-Delta 

 

The basic function of the satellite flaring data software is to detect the amount of gas flared on daily 

basis. Which includes the amount of carbon-dioxide (CO2) emitted from the flared gases, economic 

value of the flared gases as well as the potential power generation from the flared gases.  

Table 1 shows the amount of CO2 respectively emitted in Edo, Delta, Rivers, Bayelsa, Akwa-Ibom, 

Imo and Abia state. Within these periods under study (2012 - 2022), Niger-Delta region has 

cumulatively flared 2,180,677,000 MSCF of natural gas with the release of 115,749,500 Tonnes of CO2 

in the air space within the study period. The trend revealed Delta state taking the lead on the amount of 

emitted CO2 from flared gases within the period of 2018 till 2022. This is closely followed by Rivers 



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state and Bayelsa state at the second and third place.  

Apparently, (195,300,000 MSCF; 10,253,100 Tones), (809,300,000 MSCF; 43,000,000 Tones), 

(638,700,000 MSCF; 34,000,000 Tones), (377,300,000 MSCF; 20,000,000 Tones), (52,400,000 MSCF; 

2,780,300 Tones), (101,000,000 MSCF; 5,359,000 Tones) and (6,677,200 MSCF;357,100 Tones) were 

the flared volume and emitted CO2 volume respectively emitted from Edo State, Delta State, Rivers 

State, Bayelsa state, Akwa-Ibom state, Imo state and Abia state. The result showed 809,300,000 MSCF 

of natural gas has been flared for the 11 year period with a release of 43,000,000 tonnes of CO2 in Delta 

state alone where the investigation was carried out. The study area is a community in Kwale area 

located in Delta state where flaring activity is done on daily basis and at different locations, which 

poses great concerns on human’s lives at close proximity to these flaring sites. 

4.2 pH of 33 Harvested Rain Water Samples along X1, X2, X3 and Mean (ẍ) 

The lower the pH of a substance the stronger its acidity, and the higher the pH the higher the alkalinity 

of that substance. In this work, a pH value of 5.6 is the mean used to analyze the measured pH of the 33 

water samples harvested at axis X1, X2 and X3 as shown in figure (3). Clean Rain water  has a pH of 

5.6 (Singh & Agrawal, 2007; Abbasi, et al., 2013; Xuan et al., 2021; Al Hameli et al., 2022). pH 

evaluated on the harvested rain water samples ranges between 4.56±0.06 to 5.10±0.06, which are 

indisputably below clean rain water pH of 5.6 and are all acidic. 

Figures 9, 10, 11 & 12 are four graphical representation of the measured pH along the three axis of 

evaluation, X1,X2,X3 and the mean pH  

{ẍ=(X1,X2,X3)/3}. 

 

 

 

 

 

 

 

 

 

 



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Figure 9. pH Measurement along X1 Axis           Figure 10. pH Measurement along X2 Axis  

 

 

 

 

 

 

 

 

 

 

 

Figure 11. pH Measurement along X3 Axis Figure 12. Mean pH Estimate for X1.X2 and X3 Axis 

 

Figures 9, 10, 11 & 12 disclose stronger acidity near the flare location, which eases slowly away from 

it. This could be attributed to the phenomenon known as dry and wet deposition as well as pollutant 

plume dispersion. In dry deposition process, the pollutants settles/fall under gravitational influence 

usually close to the point of origin (source of generation), where it reacts and acidify water body or soil 

in contact. In wet deposition, the pollutant got scavenged in the cloud, travels by dispersion and falls 

wet at some distance from the generated location due to the influence of wind. 

 

 

 

 



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Figure 13. Overview pH Measurement along the Three Axis 

 

4.3 Risk Matrix Evaluation Results 

The calculated standard deviation of the 33 rain water samples and the Risk Rating results using the 

evaluation tools (Risk Assessment Matrix, Risk Factor) are displayed as shown in Table 4. 

 

Table 4. Risk Rating and Control Measure 

# Deviation 

D:@X1 

Deviation 

D:@X2 

Deviation 

D:@X3 

% Mean Ď: 

@X1,X2,X3 

Severity 

(S) 

Prob. Of 

Impact 

(Pf) 

Risk 

Factor 

(RF) 

Risk 

Rating 

RIR) 

Remark/Panacea 

1 29.8496 31.3572 28.9451 30.0506 3 E 3E High Stop Gas Flaring/ 

Capture & Sequester CO2 

2 22.3118 28.9451 23.8194 25.0254 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 

3 20.5028 22.0103 22.9149 21.8093 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 

4 23.8194 20.8043 27.4375 24.0204 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 

5 23.8194 22.3118 20.8043 22.3118 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 

6 19.2967 20.8043 19.8998 20.0003 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 

7 25.9299 19.5982 20.5028 22.0103 3 D 3D High Stop Gas Flaring/ 

Capture & Sequester CO2 



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8 18.6937 21.7088 17.1862 19.1962 5 B 5B Medium Stop Gas Flaring/ 

Capture & Sequester CO2 

9 15.3771 20.5028 17.1862 17.6887 4 B 4B Medium Stop Gas Flaring/ 

Capture & Sequester CO2 

10 18.9952 17.4877 15.0756 17.1862 4 B 4B Medium Stop Gas Flaring/ 

Capture & Sequester CO2 

11 15.3771 17.4877 16.2816 16.3821 3 C 3C Medium Stop Gas Flaring/ 

Capture & Sequester CO2 

 

 

Figure 14. pH Standard Deviation along the Sampling Points 

 

The main objectives of Risk Assessment Matrix is to identify potential vulnerability to environment 

and health followed by defining situations management, compare alternatives, provide knowledge on 

patterns of events and to identify critical parts of the operations. Risk Assessment Matrix evaluated the 

magnitude of the deviation of the experimental results from instituted standards. It weighs the severity 

of potential risk against the probability or likelihood the risk might occur. In Table 2, a scale of 

consequences of 0, 1, 2, 3, 4 & 5 were used to designate increasing severity at the vertical axis, and 

likelihood scale of A,B,C,D & E at the horizontal axis that designated the probability of the adverse 

effects  on the people, environment and ecosystem.  

The Risk Matrix Evaluator was utilized to generate the Risk Factor (RF) from the evaluated Standard 

Percentage Deviation (SPD) of the rain water pH along axis X1, X2 and X3 as shown in Table 3. This 

is considered reliable tool for analyzing and standardizing quantitative risk by categorizing all threats to 

safety, health, and environment based on their deviation from the acceptable limit. The Risk Factor (RF) 



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was estimated from equation (3.2) by multiplying the “Severity in the vertical column to the Likelihood 

in the horizontal row” and consistently noting the corresponding color codes in the Risk Matrix 

Evaluator. For example, the ranking codes 2A, 3A and 4A are same as 2xA, 3xA and 4xA respectively.  

Equation (3.1) was used to calculate the Standard Percentage Deviation (SPD) with 5.6 as the mean 

rain water pH. The evaluated SPD along X1, X2 and X3 axis ranges from 15.3770% - 29.8496%, 

17.4877% - 31.3572% and 15.0756% -30.0506% respectively. From the results, the calculated Mean 

Standard Deviation ranges from 16.39% - 30.05%, which falls within the BLUE and YELLOW color 

coded zones. 

The deviation at the BLUE zone is designated (10.01-20%), which covers 2C, 2D, 2E, 3B, 3C, 4B and 

5B color coded background as shown in Table 2. For analytical purpose, the deviation is distributed 

amongst the RF which is seven in number within the BLUE zone. This is done by first calculating the 

deviation difference and dividing it by the total number of RF in that zone, followed by apportioning 

the common factor to each of the risk factors, i.e.,{(20-10.01)/7=1.43%}. The value “1.43” is added 

successively to each of the RF’s. The range of application of 2C, in the BLUE code zone is: 

2C=(10.01%-11.44%) which means 2C lies within 10.01% to 11.44%. Others 2D, 2E, 3B, 3C, 4B and 

5B are designated 2D=(11.45%-12.87%), 2E=(12.88%-14.3%), 3B=(14.44%-15.87%), 

3C=(15.88%-17.31%), 4B=(17.32%-18.75) and 5B=(18.76%-20%)}.  

In the same vein, at the YELLOW coded zone, the deviation ranges from (20.1-50%), with the risk 

factors (3D, 3E, 4C, 4D & 5C) and having {(50-20.01)/5=5.98%} as the common factor. The range of 

application of 3D, 3E, 4C, 4D, & 5C in the YELLOW coded zone are {3D=(20.1%-26.08%), 

3E=(26.09%-32.07%), 4C=(32.08%-38.06), 4D=(38.07%-44.05) and 5C=(44.06%-50%)}. The mean 

deviation (Ď) value “30.0506% and 25.8194%” in roll 1 and 2 of Table 4 falls within the RF “3E and 

3D” respectively. Hence the Risk Factors (RF) for the calculated mean deviation in table 4 all falls 

within 3C, 3D, 3E, 4B and 5B. 

4.4 Model Validation and Sensitivity Analysis  

The pH profile from the experimental evaluation was compared with those predicted by the model at 

same spacing, resulting to close match as shown in Figure 15. A sensitivity analysis carried out on the 

developed model predicted save residential area to be from 4.81 KM from the flare location (Figure 15). 

The model was tested at intervals of 0.1KM starting from the flare site. The predicted distance for clean 

rain water (where pH is 5.6) is from 4.81KM as shown in Appendix 1 of this report. 

The results are in tandem with the assertion by (Abassi et al., 2013; Larssen et al., 2006), “Acid rains 

and the pollutant that creates them are often transported far away by wind from their points of origin 

and the adverse effect of the pollutant reduces at some distance apart”. Again, dispersion plays a vital 

role in which the plume of the emitted pollutant travels far from the point of generation to points they 

undergoes some form of chemical reactions. The extent they travel is a function of the pollutants 

dispersion coefficient. 



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Figure15. Model Validation 

 

 

Figure 16. Boundary between Polluted and Unpolluted Zones for Human Habitation from Flare 

Areas 

 

5. Conclusion 

Environmental risk of emitted CO2 from flared associated petroleum gases was investigated in this 

research by harvesting 33 samples of rain water within 2KM radius from the bund wall of flares. The 

evaluated pH was analysed by Standard Percentage Deviation (SPD) and Quantitative Risk Matrix 

(QRM) evaluation methods. The present work was borne out of concern for more than two million 

(2,000,000) people residing at close proximity to flaring locations as reported in Figure 2. Flared gases 

in sensitive zones such as human residential and farm areas requires improved risk management by 

intensified monitoring, evaluation and designed mitigation plan.  

First, the study shows accumulation of CO2 in the air space of the study area as disclosed by the flare 

tracker. This is evident in Figures 2 and Table 1 of this report. It revealed 809,300,000 MSCF of flared 

gases for the 11 year period with a release of 43,000,000 tonnes of CO2 in Delta state alone. Secondly, 



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it revealed decreasing acidification of acid rain away from the flare location as shown by the 

experimental data evaluations. Finally, the model predicted 4.81KM radius from flare locations for 

human habitation. 

It is worthy to note that carbon-dioxide, nitrogen oxide and sulphur oxide are the three main 

trans-atmospheric gases that precipitates rain water and making it acidic by increasing the 

concentration of hydrogen ion (H+). This work only addresses carbon-dioxide due to its deleterious and 

trans-boundary environmental concerns as a greenhouse gas. The research does not in any way 

undermine the effects of NOx and SOx as regards rain water acidification.  

The developed and validated risk model is a framework suitable for evaluation of safe residential zones 

in sensitive areas. The Physicochemical parameters should be assessed based on the criticality of the 

Risk Factor (RF). The response of the risk screening model may presumably differ in other Niger-Delta 

states due to differences in the volume of emitted flare gases as shown in Table 1. The study area was 

chosen because of high flaring volume on daily basis as compared to other areas. 

The remedy/panacea is to stop gas flaring and/or put control measures in place. One of the control 

measures is by initiating Carbon Capture and Sequestration (CCS) projects in Niger-Delta region of 

Nigeria, so as to meet the 2050 Net-Zero Goals. Hydrocarbon exploration, production and processing 

in Niger-Delta region of Nigeria started since 1957, which has led to reservoir depletion and 

abandonment. Some of the depleted reservoirs in Niger-Delta brown fields are presently termed 

Marginal Fields. Nigeria has not less than 251 Marginal fields (Mobolaji & Okoro, 2020), some of 

which are suitable for Carbon Capture and Geological Storage (CCGS), to reduce CO2 emissions and to 

achieve 2050 Carbon Neutrality goal.  

Besides Saline Aquifers, the depleted gas or oil reservoirs are proven to be suitable for implementation 

of CO2 geo-sequestration in Enhanced Gas Recovery or Enhanced Oil Recovery. Umar et al. (2020), 

Davis et al. (2022), assessed the potential for CO2 geo-sequestration in Niger-Delta Basin, using 

seismic and well information data from wells in Agbada formation. The results were compared to 

formation basin screening criteria reported by (Bachu, 2003; CO2CRC, 2008). The assessments rated 

Niger-Delta formation “Very Good” and “Excellent” depending on the screened criteria and parameter. 

Hence Niger-Delta formations are safe for geological storage of CO2. 

 

Acknowledgement 

The authors wish to thank Petroleum Technology Development Fund (PTDF) of Nigeria, for the 

studentship and the inputs of Petroleum and Gas Research Group of University of Salford, Manchester, 

United Kingdom. 

Declaration of Conflicting Interests 

The author(s) declared no conflicts of interest with respect to the research and publication of this 

article. 



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Appendix 1 

Results of sensitivity analysis on model 

B0 Bi 
DISTANCE, Xi 

(KM) 

RAIN WATER 

ACIDITY, p.H 

0.1856 4.7018 2.0 5.0730 

0.1856 4.7018 2.1 5.0916 

0.1856 4.7018 2.2 5.1101 

0.1856 4.7018 2.3 5.1287 

0.1856 4.7018 2.4 5.1472 

0.1856 4.7018 2.5 5.1658 

0.1856 4.7018 2.6 5.1844 

0.1856 4.7018 2.7 5.2029 

0.1856 4.7018 2.8 5.2215 

0.1856 4.7018 2.9 5.2400 

0.1856 4.7018 3.0 5.2586 

0.1856 4.7018 3.1 5.2772 

0.1856 4.7018 3.2 5.2957 

0.1856 4.7018 3.3 5.3143 

0.1856 4.7018 3.4 5.3328 

0.1856 4.7018 3.5 5.3514 

0.1856 4.7018 3.6 5.3700 

0.1856 4.7018 3.7 5.3885 

0.1856 4.7018 3.8 5.4071 

0.1856 4.7018 3.9 5.4256 

0.1856 4.7018 4.0 5.4442 

0.1856 4.7018 4.1 5.4628 

0.1856 4.7018 4.2 5.4813 

0.1856 4.7018 4.3 5.4999 

0.1856 4.7018 4.4 5.5184 

0.1856 4.7018 4.5 5.5370 

0.1856 4.7018 4.6 5.5556 

0.1856 4.7018 4.7 5.5741 

0.1856 4.7018 4.8 5.5927 

0.1856 4.7018 4.9 5.6112 

0.1856 4.7018 5.0 5.6298 

0.1856 4.7018 5.1 5.6484 



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0.1856 4.7018 5.2 5.6669 

0.1856 4.7018 5.3 5.6855 

0.1856 4.7018 5.4 5.7040 

0.1856 4.7018 5.5 5.7226 

0.1856 4.7018 5.6 5.7412 

0.1856 4.7018 5.7 5.7597 

0.1856 4.7018 5.8 5.7783 

0.1856 4.7018 5.9 5.7968 

0.1856 4.7018 6 5.8154 

 


