| Abstrakt: |
Urban transport is a major human activity that emits pollutants into the ambient air and this is of major concern to the environment and health. The urban transport-related pollutant levels are globally expected to grow faster owing to the growth in the economy, improvement in infrastructure, rapid urbanisation and increases in per capita transport demands in cities, especially those in low- and middle-income countries (LMICs) like Nigeria. This paper aimed to explore how the metropolitan structure of Abuja, socio-spatially defined by the road-links between the city's major residential densities and the CBD and between the suburbs and the main city, shaped the transport-related ambient air pollutant levels in the city. The study adopted a quantitative method involving three data sets. These included gas pollutant parameters such as CO, NO2, NH3, H2S, O3 measured by an Aeroqual series 500 instrument and particulate parameters such as PM 1, PM 2.5, PM 4¸ PM 7, PM 10 and TSP measured by an Aerocet 531S instrument; traffic volume counts (TVC) of different vehicle categories captured by video cameras; and microclimatic factors including relative humidity (RH), wind speed (WS) and temperature (Temp.) measured by an Extech 45,170 instrument. These were primarily and concurrently collected at the same points along the road-links in the city. A purposive sampling technique was adopted to select Phase 1 of the 5 phases of the Physical Development Plan for Abuja. Stratified sampling was used to select 3 residential districts including Wuse, Garki and Maitama districts out of the 10 districts in Phase 1, to represent high, medium, and low population densities respectively. The arterials that linked the selected districts with the CBD were purposively sampled to form 'districts-to-CBD road-links'. These included Herbert Macaulay, Ahmadu Bello and Shehu Shagari Ways respectively. The arterials that linked the major suburbs such as Karu, Gwagwalada and Kubwa with the main city were also purposively sampled to form 'suburbs-to-city road-links'. These included Keffi, Airport and Kubwa Roads, respectively. Two residential and one green area land uses were identified to serve as control areas. The Linear Regression Model, Correlation Test, Multivariate Analysis of Variance (MANOVA) and Simple Descriptive Statistics using SPSS Statistics Version 24 were used to analyse the data. It was found that CO, NO2, NH3, H2S, PM 2.5, PM 4, PM 7, PM 10, and TSP were positively and significantly correlated with the TVC. The O3 and PM 1 levels did not correlate with the TVC. The TVC proved higher along the suburbs-to-city road-links than along the districts-to-CBD road-links. This was found true for both the gas and particulate pollutants. The difference in the gas pollutant levels was not significant, as a P-value of.407 was obtained, however the particulates were significant as they had a P-value of.000. The gas pollutant levels were found to be significantly higher along the road-links than in both control areas, and particulate pollutant levels were found to be significantly higher along the road-links than the green area land use only, both with P-values of.000. It was also found that NO2, O3, PM 2.5 and PM 10, which had set standards by reputable agencies/organisations including the WHO, USEPA and the Nigerian Environmental Standard, Regulation and Enforcement Agency (NESREA), had exceeded at least 2 of the agencies' thresholds. Only CO was found to be below both the USEPA and NESREA thresholds. The novelty of the research was in the exploration of the unique socio-spatial definition of the metropolitan structure of the study area and its consequent pollutant level outcomes in the ambient air. Understanding this unique structural definition, which unveils the road-link categories of particular city regions that significantly determine the state of traffic and consequent pollutant levels in a metropolitan area, is relevant as it informs policy makers and planners towards the rightful urban structure-related vehicular pollutant mitigation measures. [ABSTRACT FROM AUTHOR] |
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