The Impact of Vehicular Emissions on Air Quality in Uyo, Nigeria

Mechanics, Materials Science & Engineering, September 2016

ISSN 2412-5954

The Impact of Vehicular Emissions on Air Quality in Uyo, Nigeria Aondona Paul Ihom1, a, Ogbonnaya Ekwe Agwu1, b, John Akpan John1, c 1

Department of Mechanical Engineering, University of Uyo, Uyo, Nigeria

a

paulihom@yahoo.co.uk

b

o.agwu4@yahoo.com

c

mailjohnjohn001@gmail.com DOI 10.13140/RG.2.1.1813.7845

Keywords: air quality, pollution, vehicular emission, roads, health implications.

ABSTRACT. Roadways, especially road intersections, contribute in no small way to the degradation of air quality in modern cities. This is largely due to toxic emissions from the ever-increasing number of vehicles plying these roads. For rapidly growing cities like Uyo, Nigeria, periodic and quantitative analysis of vehicular emissions may provide knowledge needed to stave off disastrous air pollution. Consequently, this study characterised vehicular emissions in four different locations in Uyo metropolis. Particular locations of the study were: Ekpri Nsukara Junction by Nwaniba Road (Station 1), Uyo City Centre (Station 2), Ikot Ekpene Road by Udi Street (Station 3) and Edet Akpan Avenue by Oron Road (Station 4). Attair 5X Multigas Detector was used to identify and measure the air pollutant concentrations in the four stations of study from July to September 2015. The average concentration of CO obtained in stations 1, 2, 3 and 4 were 8.5 ppm, 3.58 ppm, 11.08 ppm and 3.50 ppm respectively. The highest average concentration of CO was obtained in station 3. Also, the mean concentration of NO x and SOx was less than 0.01 ppm in all four stations. These and the other pollutants measured, H2S, NH3, CO 2 and SPM, were found to be well within the habitable range of pollutant concentration as stipulated by the World Health Organization and other relevant bodies.

1. Introduction. In December 2015, a red alert, signifying very unhealthy air conditions, was triggered in Beijing, China. As part of the emergency response plan, the government reduced the number of cars on the road by half whilst consistently monitoring the air quality [1]. Three years earlier, [2] recommended reduction in vehicular emissions as a means of tackling poor air quality in China was made. Therefore, the very high levels of air pollution in places like Beijing, are partly attributable to emissions from the large number of vehicles plying the roads. Not just in Beijing, vehicular emissions are a big problem in most cities of the world today. This is because these emissions lower air quality with resultant health implications on animal and human life [3]. In the south-south Nigeria city of Uyo, vehicular traffic has rapidly increased over the last five years.

Whereas the number of vehicles in Uyo is nowhere near those in Beijing, it is instructive to carry out

Several papers have been published corroborating the fact that roadways are one of the most important sites for the emanation of dangerous pollutants emitted by vehicles ([2], [5] [8]). Significant reduction in the levels of vehicular emissions and hence air pollution are recorded when vehicle speed is reduced. [9], [10]. The impact of vehicular emissions on air quality in the Indian city of Calcutta was assessed by [11]. Vehicular emission samples collected in the city were reported to contain suspended particulate matter (SPM), NOx, SO2, CO and lead (Pb) with CO at a concentration of 3 around 7000 microgram/m3 ) as the leading pollutant [12]. The work also evaluated the effects of traffic and vehicle characteristics on vehicle emissions near road intersections. They noted that vehicular emissions depend a great deal on engine loading. Oxides of nitrogen (NOx) were found to increase with increasing engine loading. Similarly, [13], observed low CO emissions with the increase of engine capacity. [14] carried out a study very much like present work but in selected heavy traffic MMSE Journal. Open Access www.mmse.xyz

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areas in Jos, Nigeria. Of the pollutants considered, CO was found to be present in unhealthy levels.

[15] sought to correlate fuel quality improvement with air quality. The study lasted for 10 years tracing the trends in fuel quality improvements in Bangalore city of India and the resultant effect on air quality in the city. The paper reported that particulate matter and sulphur dioxide concentrations decreased as a consequence of the incremental fuel quality norms implemented during the study period. This occurred despite the near 50% increase in traffic loads.

The effect of outdoor air pollution on human health is destructive. Increase in pulmonary diseases, lower respiratory infections, lung and urinary tract cancer have all been attributed to breathing contaminated air [16].

Vehicular emissions are due to the complete or incomplete combustion of hydrocarbon fuel in vehicle engines. The combustion of hydrocarbons yields different results depending on the nature of impurities and the extent of combustion. Regardless of fuel composition and purity, the combustion reaction conforms to the general equation:

The oxidiser is commonly the oxygen part of air. Where there is just enough quantity of oxygen to complete the reaction, the process is said to involve a stoichiometric amount of oxygen. Otherwise, there may be excess or inadequate amount of oxygen for the combustion process. Often, there is excess oxygen and the reaction is limited by the amount of fuel available. On the other hand, with insufficient supply of oxygen, combustion is terminated by the inadequacy of the oxidiser. The products of combustion are different in both cases.

Complete combustion occurs where there is at least the stoichiometric amount of oxygen required for the process. The products of complete combustion of hydrocarbon fuels are carbon dioxide and water [4].

Incomplete combustion is the result of inadequate supply of the oxidizer (oxygen). Carbon monoxide and carbon are produced instead of carbon dioxide. The products of combustion also include, among others, oxides of nitrogen and oxides of sulphur.

Consequently, the constituents of vehicular emissions are many and varied, some more dangerous than others. These contribute in no small way to the reduction of air quality in large and growing cities of the world. Little wonder that in 2014, the World Health Organisation (WHO) reported several cases of death related to air pollution globally [3].

Such reports are often based on data obtained from the most advanced countries of the world. The extent of damage done in less affluent and developing countries are largely not considered. This void needs periodic completion especially as rural-urban migration is high in such cities. The main objective of this study then, is to determine the levels of concentration of the different air pollutants resulting from vehicular emissions in Uyo, Nigeria and compare them to safe standards so that wellinformed and appropriate action or attention is given as quickly as possible before very dangerous levels are reached. Four key high traffic areas in Uyo metropolis were identified and the research work was confined to these four stations.

2. Materials and Method.

Materials and Equipment. Equipment for detecting and characterising pollutants in vehicular emissions have become commonplace even if expensive. The Attair 5X Multigas detector, a portable device owned by the Research and Development Laboratory of the Ministry of Science and Technology, Uyo, was used in detecting the amounts of NH3, H2S, NOx, SOx, CO and CO2 in four high traffic areas of the city. The study areas were: Ekpri Nsukara Junction by Nwaniba Road, Uyo Town Centre, Ikot-Ekpene Road by Udi Street and Edet Akpan Avenue by Oron Road.

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Mechanics, Materials Science & Engineering, September 2016

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Method. The catalytic sensor of the Multigas detector when turned on and exposed to the environment is capable of detecting and displaying readings of the gaseous pollutant concentration in the surroundings. Readings were taken in the monitoring stations over a period of three months (July September, 2015). Twice during every month of study, the air quality index parameters were measured during periods of peak vehicular activity in each station.

The amount of suspended particulate matter in these study areas were determined using a less to cool in a desiccator for half an hour before weighing and the result recorded as W1.

The filter paper in the petri dish was placed uncovered at a strategic position at a point of interest for a period of 2 hours. At the expiration of the period, it was covered and taken to the laboratory. The set-up was dried in the oven at the same temperature (105oC) for 15minutes and then removed from the oven and allowed to cool in the desiccator for 30mins before weighing and the result recorded as W2. Using the formula below, the concentration of suspended particulate matter was calculated.

(1)

3

3

where SPM W1 and W2

;

are respectively, the initial and final weight of filter paper in grams;

V is volume of petri dish in m3.

3. Results and Discussion.

Results. The results of the study are presented below:

Average Concentration of NOx and SOx in the monitored stations over 3 months

Concentration (ppm)

0.03 0.025 0.02 0.015 0.01 0.005 0 Station 1

Station 2

Station 3 NOx

Station 4

SOx

Fig. 1. Average Concentration of NOx and SOx in the monitored stations.

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Average concentration of CO, H2S and NH3 in the monitored stations over 3 months

Concentration (ppm)

30 25 20 15 10 5 0 Station 1

Station 2 CO

Station 3

Hydrogen Sulphide

Station 4

WHO/NAAQS 2010

Ammonia

Fig. 2. Average Concentration of CO, H2S and NH3 in the monitored stations.

Average concentration of CO 2 in the monitored stations for the period of study

Concentration (ppm)

600 500 400 300 200 100 0 Station 1

Station 2

Station 3

Station 4

Fig. 3. Average Concentration of CO2 in the monitored stations.

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3)

Average concentration of SPM in the monitored stations for the period of study

200 180 160 140 120 100 80 60 40 20 0 Station 1

Station 2

Station 3

Station 4

WHO/NAAQS 2010

Fig. 4. Average Concentration of SPM in the monitored stations.

Discussion. Seven different air quality index parameters were examined across the selected four stations. In all charts and tables, the amounts of NOX, SOX, CO, CO2, H2S, NH3 were measured in part per million (ppm) whereas the values of suspended particulate matter (SPM) was rendered in 3 ).

From Fig. 1, NOx and SOx are found to have similar concentrations across all four stations studied.

For both pollutants, the highest average concentrations occur in stations 1 and 3. The top NOx concentration was 0.020 ppm measured in stations 1 and 3. This is 20% lower than the value (0.025 ppm) considered inhabitable by the National Ambient Air Quality Standards (NAAQS). The peak concentration of SOx across the stations (0.01 ppm) is similar to the average values (Fig. 1) and falls well within acceptable levels as further illustrated in Fig. 1.

Fig. 2 displays the average concentrations of three more pollutants: CO, H2S and NH3. H2S and NH3 are found in small amounts in stations 1 and 3, but are virtually non-existent in the other two stations.

The highest concentration of CO (18 ppm) occurred in station 3. This single peak value is a little worrisome as the NAAQS benchmark is 20 ppm. However, further readings over the course of three months presented an average CO concentration of about 11 ppm a lot less disturbing Fig.. The presence of NH3 and H2S may be as a result of the waste bins containing biodegradables close to where the readings were taken. Nevertheless, the levels of all three pollutants recorded were found to be well below dangerous values. The highest average concentrations occur in stations 1 and 3.

Compared to the National Ambient Air Quality Standards (NAAQS), these peak concentrations are well within acceptable levels as further illustrated in Fig. 1.

Fig. 2 displays the average concentrations of three more pollutants: CO, H2S and NH3. H2S and NH3 are found in small amounts in stations 1 and 3 but are virtually non-existent in the other two stations.

The presence of NH3 and H2S may be as a result of the waste bins containing biodegradables close to where the readings were taken. Nevertheless, the levels of all three pollutants recorded were found to be well below dangerous values.

The concentration range of CO2 is between 276 and 384 ppm as shown in Fig. 3. CO2 is largely implicated in global warming which is why it was evaluated. Compared to the NAAQS, the highest value of 384 ppm observed in station 1 on day 3 is 36 % less than the acceptable limit of 600 ppm (WHO and NAAQS, 2010).

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The results for suspended particulate matter were scattered over the duration of the study. This was partly due to the method of measuring this index, a procedure that did not take into account the prevailing wind direction. The average values as shown in Fig. 4 as well as the peak value recorded were all within a very safe range compared to the NAAQS. Summary. One of the major sources of air pollution in growing cities like Uyo, Nigeria is vehicular emissions. Understanding and evaluating the nature and concentration of vehicular emissions is therefore important in predicting city air quality. This work determined, using the Multi-gas detector, the different types and concentration of each pollutant in four separate study areas in Uyo over a period of three months. The air pollution index parameters considered were: oxides of nitrogen (NOX), oxides of sulphur (SOX), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulphide (H2S), ammonia (NH3) and solid suspended particulate matter (SPM). The study was carried out across the four areas, which are the busiest road intersections in Uyo. Across the four locations, stations 1 and 3 consistently present significantly higher levels of pollutant concentration than stations 2 and 4. However, it appears there may not be worrying concern of immediate nature concerning air pollution in the city as emission levels are found to be below the hazardous range set by the World Health Organisation and other relevant bodies.

Acknowledgement. The authors wish to acknowledge with thanks the contributions of the staff of Ministry of Science and Technology Uyo Akwa Ibom State who was assigned to us during the course of this study. We appreciate you for painstakingly ensuring that all the needed measurements were taken and at the right time.

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Cite the paper Aondona Paul Ihom, Ogbonnaya Ekwe Agwu & John Akpan John (2016). The Impact of Vehicular Emissions on Air Quality in Uyo, Nigeria. Mechanics, Materials Science & Engineering Vol.6, doi: 10.13140/RG.2.1.1813.7845

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