Abstract
BackgroundThe economic growth and social interaction of many developing countries have been enhanced by vehicular transportation. However, this has come with considerable environmental cost. The vehicular emissions of gases such as carbon monoxide (CO), sulphur dioxide (SO2), nitrogen oxide (NOx) and volatile organic compounds (VOC’s) among others are associated with vehicular transportation. The resultant effect can lead to respiratory infections in humans, as well as growth inhibition and death of animals and plants. An investigation was conducted to evaluate the impact of vehicular air pollutants on some selected roadside tree species in the Kumasi Metropolis, Ghana. Ficus platyphylla, Mangifera indica, Polyalthia longifolia and Terminalia catappa, which were abundant and well distributed along the road sides, were selected for the study. Three arterial roads in the Kumasi Metropolis, namely Accra Road (Arterial I), Offinso Road (Arterial II) and Mampong Road (Arterial III), were considered as different traffic volumes experimental sites. The KNUST campus was selected as a control site. Diurnal analysis of CO, NO2, SO2 and VOC was monitored in the sample sites. Three replicates of each tree species were defined at a distance 10 m away from the edge of the road. Physiologically active leaves (20 to 25) from each tree species replicate were harvested for physiological and biochemical determination.ResultsThe ambient air quality data showed higher levels at the arterial road sites, which were severely polluted based on air quality index. The biochemical studies revealed reductions in leaf total chlorophyll and leaf extract pH whilst leaf ascorbic acid and relative water contents increased at the arterial road sites.ConclusionIt was found that the plants’ tolerant response level to vehicular air pollution was in the order T. catappa > F. platyphylla > M. indica and P. longifolia. Based on anticipated performance index, it was revealed that M. indica, F. platyphylla and T. catappa might be performing some level of air cleaning functions along the arterial roads. Whilst P. longifolia was poor and unsuitable as a pollution sink.
Highlights
Vehicular emissions in developed countries have been largely controlled by improvement on vehicle parts and fuel content
The concentrations of the various ambient air pollutants were greater at the arterial roads compared to quite minimal levels recorded at the control site; the difference in mean values among the arterial roads and control sites was statistically significant for carbon monoxide (CO) and Sulphur dioxide (SO2) (p < 0.05), but not significant for NO2 and Volatile organic compounds (VOC) (Table 3)
Polyalthia longifolia was classified as intermediately tolerant in Arterial road II and control site using Padmavathi’s approach; on re-categorisation, this tree species were sensitive to the vehicular air pollution
Summary
Vehicular emissions in developed countries have been largely controlled by improvement on vehicle parts and fuel content. Such cannot be said of developing countries, where many old and poorly maintained vehicles ply the roads, coupled with the use of poor grade quality fuel. The economic growth and social interaction of many developing countries have been enhanced by vehicular transportation. This has come with considerable environmental cost. An investigation was conducted to evaluate the impact of vehicular air pollutants on some selected roadside tree species in the Kumasi Metropolis, Ghana. Active leaves (20 to 25) from each tree species replicate were harvested for physiological and biochemical determination
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