Pollution Synergy from Particulate Matter Sources The Harmattan

European Journal of Scientific Research ISSN 1450-216X Vol.23 No.3 (2008), pp.465-473 © EuroJournals Publishing, Inc. 2008 http://www.eurojournals.com/ejsr.htm Pollution Synergy from Particulate Matter Sources: The Harmattan, Fugitive Dust and Combustion Emissions in Maiduguri Metropolis, Nigeria Dimari, GA Department of Chemistry, University of Maiduguri, Maiduguri, Nigeria E-mail: dimarigoni@yahoo.com Tel: +2348030748618 Hati, SS Department of Chemistry, Gombe State University, Gombe, Nigeria E-mail: stevehati@yahoo.com Tel: +2348057542206 Waziri, M Department of Chemistry, BAI University, Damaturu, Nigeria E-mail: maimunakadai@yahoo.com Maitera, ON Department of Chemistry, University of Maiduguri, Maiduguri, Nigeria E-mail: olivermaitera@yahoo.com Abstract Pollution synergy from the concurrence of the Harmattan, fugitive dust and combustion emissions was investigated in this work. The study area, Maiduguri metropolis, is located in the regions of high Harmattan distribution of West Africa. A total of 12 sampling stations were used in this work, which consisted of traffic circles/junctions and outskirt control stations during the Harmattan seasons of 2006 and 2007. The results of pollution indicator parameters investigated, i.e. particulate matter deposition rates, sulphate and heavy metal (As, Cd, Cr, Cu, Fe, Ni and Pb) concentrations show, in most cases, a significant level of increases which is indicative of an aggravation of atmospheric air pollutants during the Harmattan seasons which portends consequential implications for human health and environment. Keywords: Synergy, deposition rates, heavy metals, sulphate, atmosphere, pollution 1. Introduction The concurrence of Harmattan, fugitive dust and other particulate emissions such as automobile exhaust fumes is a paradigm of synergic processes in atmospheric air pollution. These processes are a combination of biogenic and anthropogenic activities, in which the later presents a more complex issue that has drawn international attention in recent years, especially with regard to climate change. Pollution Synergy from Particulate Matter Sources: The Harmattan, Fugitive Dust and Combustion Emissions in Maiduguri Metropolis, Nigeria 466 In Nigeria, the Harmattan (dry dust-laden atmosphere) occurs from November to March each year as experienced in most parts of West Africa (Dajab 2006; He, et al. 2007). The Harmattan is known to rise in the Sahara desert and is carried south by winds from that area (Harris, 1967); storm activities in the Bilma and Faya Largeau area in the Chad basin raise large amounts of dust into the atmosphere, which is then carried southwest by the predominant winds (Alfeti and Resch 2000). On the other hand, fugitive dust and automobile emissions results from the complex interplay between wind and anthropogenic activities that generates dust or particulate matter (PM) which is suspended in the atmosphere. Anthropogenic PM emanates primarily from soil that has been disturbed by wind or human activities, such as earthmoving and vehicular traffic on both paved and unpaved surfaces. Generally, the entity, PM is a mixture of particles in which differentiation exist only in source, size, composition, and properties (USEPA, 2004a; IDEQ 2008). The compositions of PM is complex, consisting of both inorganic and organic chemicals, as well as microbial entities, and have been well documented (USEPA, 2004a, Kaufman, et al. 2005, Centeno, et al. 2006). PM in the atmosphere affects visibility to less than a hundred meters especially during the Harmattan (Dajab 2006, Ogunseitan, 2007). It impart certain electrical effects (Harris, 1967; Ette, 1971), which affects radio frequency waves (Dajab 2006) and on equipment such as the solar water heater (Dandakouta, et al. 2008). Health effects of PM is greatly associated with its size and weight, when inhaled, PM10 (particle size of <10μm) travel to deep parts of the lungs and remain there, contributing to respiratory illness, lung damage, and even premature death in sensitive individuals (USEPA, 2004b). Man breaths between 10 and 25cm3 of air daily and any toxins present are also inhaled (Radojevic and Bashkin, 2006). Extensive research has been conducted on PM during the Harmattan season in Nigeria (McTainsh, 1980, Adepetu, et al. 1987, Adedokun, et al. 1989; Ayodele, 2002) and in neighboring West African country (Oduro-Afriyie and Anderson, 1996; Breuning-Madsen and Awadzi, 2005). Ogugbuaja and Goni (1999) and Ogugbuaja and Barsisa (2001) have determined the elemental contents of suspended particulate matter from Maiduguri metropolis on an annual basis with elemental enrichment factors. In this study, PM represents total suspended particulates falling to the ground during the Harmattan season. This was used to deduce the combined atmospheric air pollution influence of the Harmattan, fugitive dusts and automobile emissions by assessing the mass depositions, some heavy metals and sulphate concentrations of PM collected at high volume traffic circles/junctions in Maiduguri metropolis. 2. Materials and Methods 2.1. Study Area Maiduguri is located on Longitude 13º 10’ E and Latitude 11º 50’ N (Google Earth, 2008), it is known to be underlined by the sediments of the Chad basin and a semi-arid climate characterized by long dry season short rainy season (Papka, 1984). The metropolis has an estimated population of 521492 (FRN, 2007). A total of 12 sampling stations were used in this study. Four stations were simply located on the basis of outskirts positions of about 20 km from the metropolis and served as control, while the other eight stations located on the basis of high traffic circles/junctions. These sampling stations were located on the satellite map (Figure 1B) using Geko 101 (2003) with position accuracy of 15metres (49fts) RMS. 467 2.2. PM Sampling Dimari, GA, Hati, SS, Waziri, M and Maitera, ON PM sampling was carried out according to methods described by Breuning-Madsen and Awadzi (2005) with modifications. It consisted of the use of about 10 cm deep sterile plastic jugs, filled up to 3 cm with laboratory water. Each jug was protected from contamination: well fitted on lamppost at about 5 feet above the ground and with the inlet area of 0.12 m2 covered with a thin 1cm mesh. At each sampling station, a composite PM sample from 4 jugs was collected from a pair of lampposts about 100 m apart on which 2 jugs are placed in alternate directions. Sampling was conducted on a 2 week basis for the Harmattan seasons of 2006 and 2007. Samples collected were subjected to the determination of total PM deposition per unit area, sulphate and heavy metals (As, Cd, Cr, Cu, Fe, Ni and Pb) concentrations. 2.3. Analyses The water samples from the jugs were evaporated in large glass beakers. In some samples contaminated with insects were removed by floatation procedures and decanted from a water filled beakers before analysis. Samples were dried at about 80ºC, weighed and calculated as total mass weight of suspended PM falling to the ground per unit area (g/m2). Turbidimetric technique was used for the determination of sulphate content in the PM samples. About 5g of PM sample was extracted into 40 cm3 distilled water, warmed at 70ºC for about 15 min and filtered as described by Radojevic and Bashkin (2006). The filtrate was analysed for sulphate content using the HACH® DR/890 colorimeter following SulfaVer 4 Method (HACH, 1997-2007). Standard method of Flame Atomic Absorption Spectroscopy (FAAS) was used to determine the heavy metals content. The Shimadzu AA-6800 equipped with ASC-6100 auto sampler and airacetylene atomization gas mixture was used for the analysis. About 2g PM sample was extracted into 40% acidified (nitric and hydrochloric acid) distilled water, completed in 120ºC oven after 2 hr. Analysis was conducted according standard procedures described by SC (2000). Each analysis run was carried out in replicates. 2.4. Data Analysis Results obtained were expressed as mean and statistically analysed for significance in variations between sampling stations. The t-test was used for variations between control and traffic circles/junctions, while variations between sampling stations by analysis of variance (ANOVA) with Bonferroni post hoc test using coupled Microsoft Excel+Analyse-it v. 2.10 (Analyse-it®, 2007). Variations were considered significant at p<0.05. Pollution Synergy from Particulate Matter Sources: The Harmattan, Fugitive Dust and Combustion Emissions in Maiduguri Metropolis, Nigeria Figure 1A: Distribution of Harmattan in West Africa Figure 1B: Map of Maiduguri Metropolis Showing Sampling Stations Located on Google Earth 2008 468 N Maiduguri Nigeria Source: Ogunseitan, 2007 3. Results The results of PM deposition rate (Figure 2) show variations between the months of the Harmattan seasons of 2006 and 2007 in Maiduguri metropolis. Generally, there was a higher TCJ-PM deposition rates than the OC-PM in all the Harmattan months, which was statistically significant (p<0.05) in the months of January and February by t-test. In TCJ-PM between the months: February and November; February and December by ANOVA were significant. Except in February and November, no significant variation was recorded for OC-PM by ANOVA. However, the month of February presented the highest mean deposition rates of 34.5 g/m2 and 24.20 g/m2 for TCJ and OC PM respectively. On the whole, an average deposition rate of about 26g/m2 was recorded at TCJ and 18.90g/m2 at OC 469 Dimari, GA, Hati, SS, Waziri, M and Maitera, ON stations. This indicates about 16% higher deposition rates influenced by anthropogenic activities during the Harmattan seasons of 2006 and 2007. Figure 2: PM deposition rates at traffic circles/junctions (TCJ) and outskirts control (OC) sampling stations in Maiduguri metropolis + significant (p<0.05) t-test between TCJ and OC monthly * significant (p<0.05) ANOVA Figure 3 show the results of sulphate concentrations in the PM samples. It reveals higher sulphate concentrations in all TCJ-PM samples than in the OC-PM samples. Figure 3: Sulphate concentrations in PM samples collected at traffic circles/junctions (TCJ) and outskirts control (OC) sampling stations in Maiduguri metropolis * significant (p<0.05) ANOVA The overall increase in sulphate concentration in TCJ-PM was about 33%, and was statistically significant. This clearly indicates the high probability of synergic effect that is further supported by the results of heavy metals concentrations in Figure 4. The result show a general mean increases in heavy metal concentrations of the TCJ-PM against the OC-PM with the exception of Fe which gave a contrary result. Only the variation of Pb was significant with about 40% increase. Other metals, As, Cd, Cr, Cu and Ni show an almost steady but insignificant increases. However the increasing order of heavy metals concentration is: Ni0.65) of about 28% of total r values in the traffic circles/junctions. This was contributed by Cr-Cd, Cu-Cr, Fe-Cd/Cu, Ni-Cr and FePb (0.85) being the highest. In the control PM samples only Cu-Fe show r=0.74. These observations point out a high likelihood of associations of these metals from source composition and or emission origins. However, clearly indicated also is the contrary, high anti-correlation of As-Cd in the TCJ-PM samples. Table 1: Pearson Correlation coefficients (r) between values of heavy metals in PM samples collected at outskirt controls (OC) and Traffic circles/junctions (TCJ) in Maiduguri metropolis As Heavy metal correlations in OC-PM As Cd Cr Cu Fe Ni Pb 0.28 0.43 0.31 0.15 0.46 0.24 0.45 0.26 0.11 0.07 0.34 0.27 0.05 0.38 0.46 0.74 0.29 0.50 0.14 0.39 0.32 Cd -0.86 Cr 0.36 0.67 Cu 0.24 0.12 0.68 Fe 0.24 0.75 0.45 0.13 Ni -0.33 0.51 0.72 0.33 -0.27 Pb Heavy metal correlations in TCJ-PM 0.43 0.56 0.61 -0.11 0.85 0.34 4. Discussion The results of deposition rates observed in this study show remarkable agreement with the literature distribution of the Harmattan indicated in Figure 1A, in which Maiduguri is located in the high regions of 400-1200 kg/ha. In addition to which there is the prevalence of PM release into the atmosphere from vehicular movements on both paved and unpaved roads, automobile and power generating plant exhaust emissions, activities on open football field, and nomadic animal movements trampling the ground, road side kitchens, open air waste incineration and wood burning. Notable activities recorded 471 Dimari, GA, Hati, SS, Waziri, M and Maitera, ON within this period of study are road construction works in some major streets and the report of up to 5% increase in motorcycle registration (FRSC, 2008). The deposition values indicated in this study is higher than that reported by He, et al. (2007) on the basis of TCJ, but similar on the basis of OC. This may be due to the proximity of the study area to the dust source region of the Sahara than Ghana and the difference in the sampling stations. However, there has been the report of a general increase in the Harmattan particulate deposition that is attributed to the effects of climate change (Anuforom, et al. 2007, Imam, 2008). Comparative assessment of the results of deposition rates and the concentrations of sulphate and heavy metals evidently show no correlation of dependence on the deposition rates, but more likely on the level of activities which generate the pollution indicators, such as can be seen in the variations on Figures 2 and 3. In which deposition was highest in January but sulphate concentrations in March. The variations in heavy metal concentration reveals the predominance of true Harmattan dust in samples of OC-PM than in the TCJ-PM, similarly indicated in the works of Tiessen et al. (1991) and Królak (2000) who reported anthropogenic influence of heavy metals in suspended PM. The order of appreciation of metals in PM samples in this study was also similar to that reported by Adedokun, et al. (1989) in respect of Fe > Pb > Cu. Similar order was observed in the work of Ayodele and Gimba (2002) in respect of Cu>Ni in atmospheric particulates from Kano, Nigeria. Factors indicated to be responsible for the heavy metal variations in samples include wind force and direction (Soltan, et al. 2005). Maiduguri is not an industrialized city, however in addition to the variety of domestic inconveniences caused by the dry dusty winds that envelope everything both outdoors and indoors (Ogunseitan, 2007), the results of this study clearly indicate the anticipated synergic processes taking place during the Harmattan season. Reports in USEPA (2004a) show that several processes are involved the formation and growth of particles in the atmosphere. These include particles formation by nucleation from gas phase material and growth by condensation as gas phase material condenses on existing particles; particles may also grow by coagulation as two particles combine to form one. Gas phase material condenses preferentially on smaller particles, and the rate constant for coagulation of two particles decreases as the particle size increases. An idealized size distribution, that might be observed in traffic, showing fine and coarse particles and the nucleation, Aitken, and accumulation modes that comprise fine particles, major formation and growth mechanism of the four modes of atmospheric particle are also well documented (Wilson and Suh, 1997; USEPA, 2004a). For instance, most of the sulfate and nitrate and a portion of the organic compounds in atmospheric particles are formed by chemical reactions that occur in the atmosphere. Secondary aerosol formation depends on numerous factors, including the concentrations of precursors, such as the combustion of fossil fuel; the concentrations of other gaseous reactive species such as ozone, hydroxyl radical, peroxy radicals, or hydrogen peroxide; atmospheric conditions including solar radiation; and the interactions of precursors and preexisting particles within cloud or fog droplets or in the liquid film on solid particles. 5. Conclusion Pollution synergy from the concurrence of the Harmattan, fugitive dust and combustion emissions was investigated at TCJ regarded as points of synergy in this work. The results from indicator parameters investigated, i.e. particulate matter deposition rates, sulphate and some heavy metal concentrations show, in most cases, that there are significant increases in these pollution indicators determined. 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