Air Quality Changes and Geospatial Dispersion Modeling in the Dry Season in Port Harcourt and its Environs, Niger Delta, Nigeria

This work is a geospatial analysis of air dispersion for the purpose of establishing the concentration trend of air pollutants within the study area. Pollutants of consideration are SO2, NO2, CO, H2S, NH3, VOCs, CH4, PM2.5, PM10, TSP, while area of interest are Port Harcourt, Obio/Akpor, Eleme, Oyigbo, Etche and Ikwerre Local Government Areas. This is an approach to identify the hotspots and how they are dispersed to impact on other parts of the region. This is an attempt to predict future pollution trends, but an approach to gain understanding of the general scenarios of air quality status and how they impact on receptor areas some kilometers away from the hotspot. Pollution hotspots are locations where emissions from specific sources such as water or air pollution may expose local populations to elevated health risks and environment degradation. It indicates areas with strong pollution sources and high industrial activities of adverse effect


INTRODUCTION Pollution is defined by the European Union 1996 Council Directive on Integrated Pollution Prevention and Control
(IPPC) as "the direct or indirect introduction as a result of human activity, of substances, vibrations, heat or noise into the air, water or land which may be harmful to human health or the quality of the environment, result in damage to material property, or impair or interfere with amenities and other legitimate uses of the environment". Inorganic and organic air pollutants cause negative health and environmental effects such as respiratory ailments, premature deaths. Air pollution-related deaths worldwide are estimated to be up to 2 million per annum. Other environmental consequences of air pollution include acidification of soil and water and loss of plant and animal life. Air quality assessment studies in Nigeria have focused mainly on urban centres where industrial processes, domestic activities and traffic congestion constitute major sources of air pollution. Most of these studies are independent as there are no systematic measurements of air quality public agencies. Meteorological parameters influence aids to drive the air pollutants from the pollutant hotpots to non-sources areas (Antai et al., 2017, Everitt, 1992and Esplin, 1995. This is the trend that has put man in alert in his own environment since the air has no boundary or barrier from one man to another. The aim of this research is to assess changes in existing physical and chemical characteristic of the air quality and to determine the hotspots and assess the level of concentration of air pollutants dispersion trends in the study area. Results of geospatial analysis and generalized additive models revealed that sources of pollutants in the study areas are both localized in the up-land area and the region around the coastal area. Lugard to meet the pressing economic needs of the Europe the city, which lies at the heart of the Niger Delta, is one of the world's richest wetlands and is bounded on the south by the Atlantic Ocean, to the North by Imo and Abia States, to the East by Akwa Ibom State and to the West by Bayelsa and Delta States respectively. The spatial coverage of this study extends through beyond in Port Harcourt and its environs, Port Harcourt, Obio/Akpor, Eleme, Oyibo, Ikwerre and Etche Local Government Areas.  (Table 1) were selected in Port Harcourt and its environs using WHO's (2005) guideline for site selection studies for population density, topography, industrial clusters, and heavy traffic. All the sampling points selected were geo-referenced using GPS model 76Cx Garmin Global positioning system. Field observations were carried out visually and recorded in the field notebook. Camera was used to take photographs to show evidence of important features and activities that may be the primary sources of the air pollutants.

Validity/Reliability of Instrument
All the portable in-situ meters for the field air quality and meteorological parameters including noise level measurement were certified calibrated by the manufacturer prior to mobilization to the field data gathering. Quality assurance and control measures were carried out accurately as per the equipment manufacturer's directive and battery were fully charged.

Pollutant Mapping
Concentration levels at each location were mapped out using ArcGIS 10.2 software. The software integrated the spatial air pollutants data from the sampling points within the Port Harcourt and its environs and analyzed them as input variables for graphical presentation to produce curves or contours of air pollutants levels.

III. RESULTS AND INTERPRETATION Distribution of SO2 in Study Area in the Dry Season
In the dry season, SO2 hotspot is visible within Eleme with the highest concentration within 1.10 to 1.18ppm (Figure 1). It occupies an aerial coverage of about 3,725meters radius. It has a larger influence on Port Harcourt, followed by Obio/Akpor and Oyigbo while its minor influence is in Ikwerre as shown in Figure 1. Its least influence is on Etche area. It is predicted that the hotspot will contribute about 0.035ppm to 0.080ppm to the background concentration of SO2 in parts of Port Harcourt, Obio/Akpor, Oyigbo, Etche and Ikwerre Local Government Areas respectively. ://dx.doi.org/10.22161/ijeab/3.3.24  ISSN: 2456-1878 www.ijeab.com Page | 887

Fig.1: Distribution in SO2 of the Study Area in the Dry Season Distribution of NO2 in the Study Area in the Dry Season
In the dry season, NO2 hotspots are visible within Eleme and part of Oyigbo with the highest concentration within 0.82 to 0.88ppm (Figure 2). It occupies elongated area coverage of about 17670meters. It showed moderate influence in Obio/Akpor and Ikwerre It has a larger influence on Oyigbo followed by Etche with the least influence in Port Harcourt area as shown in Figure 2. It is predicted that these hotspots will contribute about 0.05 to 0.070ppm to the background concentration of NO2 in parts of Oyigbo, Etche, Obio/Akpor, Port Harcourt and Ikwerre.

Distribution of H2S in the Study Area in the Dry Season
In the dry season, H2S hotspot is visible within Eleme with the highest concentration within 1.70 to 1.87ppm as shown in Figure 3. It occupies an aerial coverage with a 2670meters radius and has a moderate influence on Oyigbo and its least influence is in Port Harcourt, Obio/Akpor and Etche. It is predicted that this hotspot will contribute additional 0.05 to 0.1ppm to the background concentration of H2S in parts of Port Harcourt, Oyigbo, Obio/Akpor and Etche.

Distribution of VOCs in the Study Area in the Dry Season
In the dry season, VOCs hotspot is visible within Eleme with the highest concentration within 6.26 to 6.82ppm as shown in Figure 4. It occupies an aerial coverage of about 3,850meters radius. It has a larger influence on Obio/Akpor. It has least influence on Port Harcourt, followed by Oyigbo, Etche and Ikwerre LGAs. It is estimated that this hotspot will contribute additional 0.25ppm to 0.41ppm to the background concentration of VOCs.

Distribution of CO in the Study Area in the Dry Season
In the dry season, Carbon Monoxide (CO) hotspot is visible within Eleme with highest concentration within 25.06 to 27.85ppm as shown in Figure 5. It occupies an aerial coverage with a 4350meters radius. It has a minor influence on Obio/Akpor, followed by Oyigbo and Port Harcourt. Its least influence is on Ikwerre and Etche areas. It is predicted that this hotspot contributes additional 1.1 to 2.05ppm to the background concentration of carbon monoxide in parts of Obio/Akpor, followed by Oyigbo and Port Harcourt.

Distribution of NH3 in the Study Area in the Dry Season
In the dry season, ammonia hotspot is visible within Eleme with highest concentration within 5.32 to 5.98ppm as shown Figure 6. It occupies an aerial coverage of 3500meters radius. It has a very minor influence on Oyigbo, but less on Obio/Akpor and Port Harcourt. Its least influence is on Ikwerre and Etche areas. It is predicted that this hotspot will contribute additional 0.15 to 0.2ppm to the background concentration of ammonia in parts of Oyigbo, Obio/Akpor and Port Harcourt.

Distribution of CH4 in the Study Area in the Dry Season
In the dry season, methane hotspots are visible within Eleme followed by Obio/Akpor and Port Harcourt with highest concentration within 6.86 to 7.48ppm as shown in Figure 7. It occupies an aerial coverage of 3750meters radius. It has a moderate influence on Oyigbo. It has least influence on Ikwerre and Etche LGAs. It is predicted that these hotspots contribute about 3.0 to 4.0ppm to the background concentration of methane (CH4) in parts of Oyigbo, Ikwerre and Etche.

Distribution of TSP in the Study Area in the Dry Season
In the dry season, TSP hotspots are visible within an extended area of Obio/Akpor and Eleme followed by Port Harcourt with highest concentration within 716.27µg/m 3 to 792.81µg/m 3 as shown in Figure 8. It occupies elongated aerial coverage of 26,466meters length. It has a larger influence on Ikwerre followed by Oyigbo and showed its moderate influence on Etche area. It is predicted that these hotspots will contribute additional 2.0µg/m 3 to 3.4µg/m 3 to the background concentration of TSP in parts of Ikwerre, Oyigbo and Etche.

Distribution of PM10 in the Study Area in the Dry Season
In the dry season, PM10 hotspots are visible within an extended area of within Obio/Akpor and Eleme followed by Port Harcourt with highest concentration within 501.39µg/m 3 to 554.09µg/m 3 as shown in Figure 9. It occupies elongated aerial coverage of 27200meters length. It has a larger influence on Oyigbo but less on Ikwerre and Etche. It is predicted that these hotspots will contribute about 10µg/m 3 to 25µg/m 3 to the background concentration of PM10 in parts of Oyigbo, Ikwerre and Etche.

Fig.9: Distribution of PM10 in the Study Area in the Dry Season Distribution of PM2.5 in the Study Area in the Dry Season
In the dry season, PM2.5 hotspots are visible within Eleme followed by Port Harcourt and Obio/Akpor with highest concentration within 84.15µg/m 3 to 92.19µg/m 3 as shown in Figure 10. It occupies an aerial coverage of 4100meters radius. It has a larger influence on Ikwerre and Oyigbo, but least influence on Etche area. It is predicted that these hotspots contribute about 3.5µg/m 3 to 5.5µg/m 3 to the background concentration of PM2.5 in parts of Ikwerre, Oyigbo and Etche,

IV. DISCUSSION Evaluation of Pollutants Dispersion Pattern in the Study Area in the Dry Season
The pollutants dispersion patterns in the study area in the dry season were evaluated with the aid of pollution roses and bivariate polar plots of each pollutant with respect to wind speed and wind direction. The dry season results are presented in Figures 11 (a-j) and 12 (a-j). The pollution roses and polar plots were developed using the mean concentration of each pollutant in different wind speed and percentage frequency count of wind direction categories (Munir, 2016). They were simulated with the aid of Generalized Additive Model (GAM) smoothing techniques Carslaw, (2015) that depict pollutant concentrations as a continuous surface. Pollution roses (Figure 11 (a-j)) showed that pollutant concentrations increase with increased wind speed. Low concentrations of pollutants were obtained at low wind speed and vice-versa. This implies that wind speed has positive influence on the concentration levels of pollutants in the study area.

Fig.11(a-j): Pollution Roses of Pollutants in the Study Area in the Dry Season
The pollutant polar plots (Figure 12 (a-j)) showed that concentrations of pollutants in the area are associated with wind speed up to 3.5m/s. It is also observed from Figure 12 (a-j) that pollutant concentrations increase with increased wind speed. Surface polar plots of pollutants concentrations in the study area revealed that high concentrations of SO2, NO2, NH3, H2S and VOCs are associated with the south-west and southeast directions and are dispersed toward the north-east and north-west directions. This may imply that sources of these pollutants are in the southern part, which is the coastal region of the study area. Industrial activities, especially in Eleme area (refineries, petrochemical company, fertilizer companies, industrial waste management facilities, civil construction, gas flaring, and vehicular movement) and the release of black carbon (black soot) due to illegal refineries in the coastal area may be the sources of these pollutants  Similarly, concentrations of Methane (CH4) and Particulate matter (TSP, PM10 and PM2.5) are associated with both northern and southern directions. This showed that activities in the both the coastal and up-land areas are responsible for the release of these pollutants into the environment. In other words, industrial activities, vehicular exhaust emissions, civil construction, the released of black carbon (black soot) due to illegal refineries in the coastal area, gas flaring and oil and gas exploitation in Eleme, Port Harcourt, Obio/Akpor, Etche and Ikwerre areas may be the sources of CH4 and Particulate matter in the air environment of the study area in the dry season period.
(g.) (h.) V. CONCLUSION There were relatively high concentrations of air pollutants especially dominated in southern area in the dry season. Results of geospatial analysis and generalized additive models revealed that sources of pollutants in the study area are localized in the up-land area and region around the coastal area and dispersed towards the southern and northern parts of the study area in the dry season.