Spatial and Seasonal Analysis of Traffic-Related Pollutant Concentrations In
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African Journal of Agricultural Research Vol. 5(11), pp. 1264-1272, 4 June, 2010 Available online at http://www.academicjournals.org/AJAR DOI: 10.5897/AJAR09.253 ISSN 1991-637X © 2010 Academic Journals Full Length Research Paper Spatial and seasonal analyses of traffic-related pollutant concentrations in Lagos Metropolis, Nigeria Cornelius O. Akanni Department of Geography and Regional Planning, Olabisi Onabanjo University, P. M. B. 2002, Ago-Iwoye, Ogun State, Nigeria. E-mail:[email protected]. Tel: +2348037222973. Accepted 25 May, 2010 Leaf samples of Terminalia catappa L (Almond) trees dominant in Lagos metropolis, Nigeria were collected from 34 sampling points located within dominant land-uses (commercial, residential, industrial, institutional, acquisition/parks, dumpsites/incinerators and transportation) along traffic corridors and six stations located 250 m away (as control) during the short wet and short dry seasons for two years. Concentration of trace elemental pollutants: (Pb, Cd, Cu, Cr, Al, Zn, As, Hg, Fe, Mn, Mg) were determined by laboratory analyses of leaf samples. Multivariate analysis was used to test for significant geographical and seasonal variations in air pollutants. Total suspended particulate matter varied from 22.36 - 29.07 mg/m3 against WHO Air Quality Standard (AQS), 0.05 - 0.15 mg/m3; Sulphur- dioxide and Ozone varied from 1.1 - 1.73 mg/m3 and 0.01 - 0.18 mg/m3 respectively as against 0.00125 and 0.0015 mg/m3 AQS. ANOVA showed spatio-temporal variations in pollutants and significant correlation of traffic density with all metals studied (P < 0.05). Lead varied from 1.4 - 3.1 mg/m3 and 1.7 - 2.6 mg/m3, Cadmium varied from 1.7 - 3.15 mg/m3 and 0.011 - 0.1 mg/m3, Iron varied from 3.06 - 3.6 mg/m3 and 0.5 - 2.6 mg/m3, while Arsenic varied from 0.9 - 1.98 mg/m3 and 0.011 - 0.1 mg/m3 along traffic corridors and at control points respectively. Step-wise regression analyses further showed that traffic density, air temperature and land-use contributed significantly to air pollution (P < 0.05). The micro- climate of Lagos metropolis is characterised by relatively high air temperature, low wind speed and air pollution that varied according to traffic density and land-use. Concentrations of pollutants were higher than the WHO Air Quality standards and were also higher along traffic corridor than further away. Key words: Lagos metropolis, air pollution, bio-monitoring, traffic density, land-use. INTRODUCTION One of the key indicators of the quality of life is a clean purification functions as may be or may tend to be environment, which can be further disaggregated in terms injurious to human, plant or animal life, or which may of water, noise and air qualities. During the last 200 unreasonably interfere with the comfortable enjoyment of years, humans began to significantly alter the life or property or the conduct of business (Xie et al., composition of the atmosphere through pollution. 1998; Zhongan, 2006). Urban canopy pollution resulting Although air is still made up mostly of oxygen and from urbanization is one of the microclimatic problems nitrogen gases, mankind, through its pollution activities, faced in many major urban centres including Lagos has increased the levels of many trace gases and in metropolis, the air along traffic corridors where majority of some cases, released new gases into the atmosphere residents in the formal and informal sectors (petty (Akanni, 2008). Ambient air pollution in the presence of traders, street hawkers, vulcanizers, bus drivers and one or more contaminants in the outdoor atmosphere or conductors, roadside shop operators, schoolchildren, the combinations thereof in such quantities and of such police officers and traffic wardens) subsist daily to duration over and above the natural physical diffusion, conduct their daily economic activities could hardly be deposition, chemical elimination and biological regarded as fresh. The interest in air pollution is related Akanni et al. 1265 to the fact that air contains oxygen essential for life, what practicable. Active methods detect the presence of air is even more important is that air quality has a direct pollutants by placing test plants of known response and influence on human health and basic functions such as genotype in the study area. The response of plants to breathing. All pollutants discharged into the atmosphere, elevated concentrations of air contaminants is modified beyond critical concentrations, are harmful to plants, by other environmental factors and by the physiological animals and humans. In our cities, most people breathe status of the plant. Monitoring the plants directly in dirty air with gaseous contaminants linked to varying assesses the integrated effects of these factors and cardiopulmonary and cardiovascular diseases, contamination. It has however been noted that trees hyperactivity, neurobehavioral effects and even death remove gaseous air pollution primarily by uptake through (Nriagu, 1978; Massami et al., 2001; Peng et al., 2005; leaf stomata, though some gases are removed by the Osibogun, 2006). plant surface. Once inside the leaf, gases diffuse into There are several environmental concerns over intercellular spaces and may be absorbed by water films particulates in the air: (i) the dirt they produce when to form acids or react with inner-leaf surfaces. Trees also settled on the ground is annoying and requires energy remove pollution by intercepting airborne particles. Some and money for removal, (ii) They produce effects that is particles can be absorbed into the tree, though most detrimental to materials, plants and animals, including particles that are intercepted are retained on the plant man and (iii) There is concern over their effect on the surface. The intercepted particle often is re-suspended to heat balance of the earth through reflection and the atmosphere, washed off by rain, or dropped to the absorption of solar radiation. These effects are ground with leaf and twig fall. Consequently, vegetation is complicated by the fact that many of the particulates only a temporary retention site for many atmospheric remain aloft for unusually long periods and in some cases particles. Atmospheric pollution has emerged as a become permanently air-borne. Human exposures to air- problem in most African countries only in the past few borne chemicals vary widely among inhalation micro decades, its severity and impacts are still largely environment categories, which include workplaces, re- unknown, although it is believed that gaseous pollutants sidences, outdoor ambient air, transportation, recreation and acid rain have adversely affected vegetation, soils areas and public spaces. There are also wide variations and water in some areas. Despite this, the atmospheric in exposure within each category, depending on the chemistry of the tropics has been poorly studied in the number and strength of the sources of the airborne past, placing our current understanding in doubt. In chemicals, the volume and mixing characteristics of the Nigeria, empirical studies have been carried out on the air within the defined micro environment, the rate of air spatial pattern of micro climatic variables, energy exchange between indoor and outdoor air, and the rate of distribution in urban centres, thermal responses, loss to surfaces within the micro environment (Akanni comparative study of urban heat island syndrome within and Solanke, 2002). the urban canopy ( Ojo, 1978, 1981; Akanni, 1987; Ojo, Ambient air quality monitoring in urban areas have a 1988; Efe, 2004; Oke, 2004, 2004a) and bio monitoring number of objectives. One is to generate information on of air quality (Oluwande, 1977; Osibanjo and Ajayi, 1980; the spatial and temporal distribution of air pollution in Oniawa and Egunyom, 1983, 1986; Fatoki and Ayodele, urban areas. Monitoring data are then compared against 1991; Ogunsola et al., 1993; Odukoya et al., 2000 ; air quality standards to identify potential risks to human Obioh et al., 2005), none of the studies has examined health or the environment. Data indicating high pollutant the spatio-temporal and seasonal variations in air quality concentrations in certain parts of an urban area (such as of a rapidly developing metropolis. Molina, (2002) a central business district) or during certain periods of the observed that much of the technology developed in the day or year (certain months) enable policy makers to take United States and Europe can be adapted to Asian, Latin the necessary measures aimed at reducing pollution at American and African cities without the ‘trial-and-error’ these locations or during these periods. Biological costs that were incurred to reduce pollution in the monitoring has been defined as the systematic use of developed world. Studies of this nature will further enable biological responses to evaluate changes in the researchers compare urban air quality characteristics environment with the intent to use this information in within a tropical city with those of other cities in both the quality control programmes (Matthews, 1982). Biological tropical and temperate countries and achieve a desired monitoring is generally less expensive than other environmental outcome of ambient air quality that allows methods and is thus particularly suitable for long-term for adequate protection of human health and well being. monitoring over large areas without deploying Moreover, the nature of urban climates needs to be sophisticated expensive and high-level maintenance understood to be able to improve the atmospheric equipment. Biological monitoring of air pollutants can be conditions and mitigate potential adverse effects. passive or active. Passive methods provide a cost- Hence, this paper examines the spatial and seasonal effective solution for monitoring air quality by observing variations in particulate pollutants concentration in urban plants growing naturally within the area of interest at air of Lagos metropolis, Lagos state; Nigeria, by bio- locations where continuous monitoring may not be monitoring the concentration of trace elemental 1266 Afr. J. Agric. Res. Figure 1. Administrative map of Lagos showing 20 local governments.