Impact of Concentration Levels of Atmospheric Pollutants on Local Climate of Delta State, Nigeria

Studies in various regions of the world have revealed that air pollution can have a significant influence on local climate. This study therefore considers the impact of concentration levels of atmospheric pollutants on local climate of Delta state, Nigeria. Monthly and annual averaging of the daily pollutant concentrations and meteorological parameters within the period of investigation was carried out. Descriptive Statistics, correlation analysis, coefficient of determination (R 2 ) analysis and least squares regression analysis of the selected meteorological parameters with CH 4 and O 3 concentrations for the period of 2003 to 2012 and NO 2 and CO 2 concentrations for the period of 2011 to 2014 were carried out. The regression relationship was then used to obtain predicted values for the meteorological parameters within the period of investigation. The results of the descriptive statistics of annual averages of CH 4 , O 3 , NO 2 and CO 2 concentrations within the period of investigation revealed that the emission levels breached FEPA and EGASPIN limits. The results of the correlation analysis indicated that CO 2 had a strong significant positive correlation with temperature with a correlation coefficient of 0.962, while a moderate negative correlation coefficient of 0.549 was obtained for CH 4 , and very weak correlation coefficients of −0.167 and 0.077 were obtained for O 3 and NO 2 respectively. CH 4 , O 3 and CO 2 had a moderately significant positive correlation with solar radiation with correlation coefficients of 0.661, 0.571 and 0.656 respectively, while a weak negative correlation coefficient of 0.106 was obtained for NO 2 . CH 4 had a strong significant positive correlation with relative humidity with a tive correlation coefficient of 0.518 was obtained for O 3 , and a weak negative correlation coefficient of 0.317 was obtained for NO 2 . The predicted values of the meteorological parameters showed a significant level of agreement with their measured values. Therefore, among the atmospheric pollutants postulated as influencing meteorological parameters, CO 2 appears to be the most strongly significant in explaining temperature variations in this region of Niger Delta, with correlation coefficient of 96.2% and coefficient of determination (R 2 ) of 0.926, implying that CO 2 influenced 92.6% variation in temperature in this part of Niger Delta within the period of investigation.


Introduction
Air pollution is a major environmental problem facing the Niger Delta region [1]. Air pollution is the contamination of the atmosphere by noxious gases and particulates.
Studies have revealed that air pollution can have a major effect on local climate [1]. Due to the spatial distributions of atmospheric pollutants with higher concentration levels mostly found near emission sources, variations in emission and concentration levels of air pollutants can cause a significant influence on local climate [2] [3] and in some situations regional climate by means of teleconnections in the atmosphere [4]. About 8 billion cubic meters of gas is flared yearly at various oil production sites in Nigeria [1]. It has been reported that the Niger Delta region of Nigeria has more than 123 gas flaring sites making Nigeria one of the major emitters of greenhouse gases in Africa [5]. Nigeria is accountable for almost one-sixth of the gas flared worldwide [6]. Nearly 75% of Nigeria's natural gas is being flared and all occur in the Niger Delta region. The flares have contributed more greenhouse gases thereby causing climate change which could possibly lead to increased occurrence of flooding in the region [7].
There have been occurrences of acidified rain in the Niger Delta region due to the introduction of a high concentration of sulphur and oxides of nitrogen into the atmosphere [8] [9]. Combustion processes in gas flaring sites give rise to the emission of lower fractions of hydrocarbons and oxides of nitrogen and the presence of ultraviolet radiation produces smog which could cause a reduction in visibility [10].
About 45.8 billion kilowatts of heat are released into the atmosphere of the Niger-Delta from 1.8 billion ft 3 of gas daily [11]. Heat production destroys vegetation in the vicinity of the heat source [12]. [13] undertook a study on the analysis of carbon monoxide concentration levels with some selected meteorological showed that out of all the meteorological parameters studied, only wind speed showed a strong correlation with carbon monoxide.
[14] undertook a study on the use of greenhouse gases as climate proxy data in explaining variability in climate. The standard deviation of CH 4 and CO 2 concentrations showed good correlations with the years associated with warming and can be used as good climate proxies. Furthermore, [15] carried out a study on the effect of meteorological parameters on distribution of atmospheric pollutants in Bayelsa State, Nigeria. The results revealed that wind speed showed a strong correlation with O 3 and CH 4 concentration levels.
Even though some amount of work has been done on the sources and distribution of air pollutants, so far, no major study has been undertaken on the effect of atmospheric pollutants on local climate in the Niger Delta. This work is aimed at increasing research efforts on understanding the association of atmospheric pollutants and related climate and environmental impacts in the Niger Delta Area.

Data description
The data on daily methane (CH 4 ) with tropospheric ozone (O 3 ) concentration levels (for the period of 2003 to 2012) and daily nitrogen dioxide (NO 2 ) with carbon dioxide (CO 2 ) concentration levels (for the period of 2011 to 2014) used in this study were obtained from the National Aeronautics and Space Administration (NASA). The data on meteorological parameters (wind speed, solar radiation, temperature and relative humidity) for the period of 2003 to 2014 were acquired from the Nigerian Meteorological Agency (NIMET), Lagos.

Method
Monthly and annual averaging of the daily pollutant concentrations (NASA data) and meteorological parameters (NIMET data) within the period of investigation was carried out. The statistical analysis of weather parameters in this region of the Niger Delta with CH 4 and O 3 concentrations for the period of 2003 to 2012 and with NO 2 and CO 2 concentrations for the period of 2011 to 2014 were carried out. The regression relationship: was used to obtain predicted values for the meteorological parameters within the period of investigation, so that by comparing the level of agreement between the predicted and measured values, we could ascertain the reliability of the model in this part of Niger Delta. Where: Y = meteorological parameter (predicted); X = atmospheric pollutant concentration; b and a are the slope and intercept respectively and are given as:  Table 3 shows the descriptive statistics of annual averages of CH 4 , O 3 , NO 2 and CO 2 concentrations, while Table 4 shows the descriptive statistics of annual averages of selected meteorological parameters.

Impact of the Atmospheric Pollutants Concentration on Meteorological Parameters
The impact of the concentration of atmospheric pollutants on selected meteorological parameters was determined using correlation analysis, coefficient of determination (R 2 ) analysis and least squares regression analysis.

2) Least squares regression analysis
The Least squares regression analysis gives us the line of best fit enabling us to predict the behavior of the meteorological parameters. CO 2 had the highest R 2 of 0.926 with temperature, as shown in Figure 6(d).
To obtain predicted values for temperature, we substitute the values of a (intercept) and b (slope) from Figure 6  Therefore by substituting the values of CO 2 concentration into Equation (4), we obtain predicted values for temperature within the period of investigation. Table 6 shows predicted and measured values of temperature, while Figure 10 shows the graph of predicted and measured values of temperature. CH 4 had the highest R 2 of 0.437 with solar radiation, as shown in Figure 7(a).
To obtain predicted values for solar radiation, we substitute the values of a (intercept) and b (slope) from Figure 7   we obtain predicted values for solar radiation within the period of investigation. Table 7 shows predicted and measured values of solar radiation, while Figure 11 shows the graph of predicted and measured values of solar radiation.    Therefore by substituting the values of CH 4 concentration into Equation (6), we obtain predicted values for relative humidity within the period of investigation. Table 8 shows predicted and measured values of relative humidity, while Figure 12 shows the graph of predicted and measured values of relative humidity.   where Y is wind speed (predicted) and X is CO 2 concentration to obtain equation (7) as: Therefore by substituting the values of CO 2 concentration into Equation (7), we obtain predicted values for wind speed within the period of investigation. Table 9 shows predicted and measured values of wind speed, while Figure 13 shows the graph of predicted and measured values of wind speed.

Discussion
The results of the descriptive statistics of annual averages of selected meteoro-    proportional rise in CH 4 concentration is much more efficient as a greenhouse gas than a comparable rise in CO 2 concentration [14]. However, CO 2 has a greater influence than CH 4 on climate change due to its higher atmospheric concentration.
The results of the correlation analysis between the selected meteorological parameters (dependent variables) and CH 4 , O 3 , NO 2 and CO 2 concentrations (independent variables) within the period of investigation as shown in

Conclusion
Changes in emission and concentration levels of atmospheric pollutants can significantly affect local climate and in some situations regional climate by means of teleconnections in the atmosphere. Among the atmospheric pollutants postulated as influencing meteorological parameters, CO 2 appears to be the most strongly significant in explaining temperature variations in this region of Niger Delta, with a correlation coefficient of 96.2% and a coefficient of determination (R 2 ) of 0.926, implying that CO 2 influenced 92.6% variation in temperature in this part of Niger Delta within the period of investigation. The emission levels of the atmospheric pollutants breached FEPA and EGASPIN limits.