ABSTRACT
Measurement of ambient concentrations of some of the “classical” air pollutants (NO2, O3, SO2) in Niger-Delta region of Nigeria was undertaken as a step towards addressing the problem of pollution arising from exploration and exploitation of natural resources especially crude oil, found in large quantity in the region.
The results obtained showed that the annual mean NO2 concentration in all the created seventeen monitoring locations including the controls ranged from 9.27g/m3 recorded at Aladja Town to 47.03g/m3 recorded at Jakpa Junction both in Warri. Similarly, the annual mean SO2 concentration ranged from 0.94g/m3 to 5.06/gm3 recorded at Tamaga Junction in Gelegele and McDemoth Gate (Gold Star) in Warri respectively. Finally, Ozone concentration ranged from 0.05g/m3 recorded at Gelegele-Ikpokpa road in Gelegele to 0.27g/m3 recorded at Refinery yard in Warri.
The results showed that the concentrations were consistently high at some sites and low at others. Also, variability of concentration with time was observed. Taking Jakpa-Junction as an example, concentrations of the three pollutants were higher in the dry-season (December, 54.68g/m3 (NO2), 0.42g/m3(O3), 6.23g/m3 (SO2)) than the wet-season (June, 36.34g/m3 (NO2), 0.16g/m3 (O3), 3.32g/m3 (SO2)). The seasonal trend observed could be as a result of the fact that generally, the wet-season witnesses decline in traffic density and reduction in combustion processes especially bush burning due to increase in atmospheric humidity. In addition, wet-season ensures rain wash out of acid gases in the atmosphere; proper dispersion of atmospheric pollutant by meteorological factors especially wind (which increase in intensity during the wet-season); reduction in sunlight that catalyzes photochemical reaction and consequently reduction in concentration of certain pollutants e.g. Ozone, peroxy acetyl nitrate. e.t.c.
The traffic census was conducted in all the created monitoring locations in an effort to determine the relationship between the measured concentrations and traffic density. The results showed that in most of the sites in Warri, the measured concentrations were well correlated with traffic density. However, all the locations in Gelegele have negligible traffic density; yet some recorded relatively high pollutant concentration. This suggests that there were other influencing factors outside vehicular emission, the concentration of which is dependent on traffic density. Indeed gas flaring was found to be another important influencing factor in the concentrations of the pollutants especially NO2.
The concentrations measured were compared with set standards both nationally and internationally. The results revealed that for NO2, two locations, Jakpa Junction and McDermoth Gate all in Warri exceeded the WHO annual mean limit of 40g/m3. This calls for concern for further investigation of the sources of NO2 in these locations and ways to remediate the high levels. For Ozone (O3) and Sulphur dioxide (SO2), the concentrations determined were found to be lower than the set standards.
To further highlight these observations, the concentrations measured were subjected to a set of numerical analysis: inter-correlation matrix, factor analysis and cluster analysis. The results reveal that most of the sites and the periods showed positive correlation, suggesting that factor(s) responsible for the measured concentration between locations and between sampling periods were the same. Similarly, results of factor analysis identified vehicular emission, gas flaring, biogenic sources and combustion of fossil-fuel as the four major sources contributing to pollution load in Niger-Delta region. Finally, the cluster analysis classified locations into high or low pollution group as well as periods of monitoring whose groups corresponded with either the dry-season period or wet season period.
