Assessment of Air Pollution Tolerance Index of Roadside Trees in Kaduna Metropolis

Air pollution from vehicular and industrial emissions is a major environmental health concern in Kaduna metropolis, North West Nigeria, and identifying tree species with high air pollution tolerance can guide urban greening for pollution mitigation. This study assessed the air pollution tolerance index (APTI) of eight roadside tree species at two busy roads in Kaduna metropolis (Ahmadu Bello Way and Kachia Road) and compared them with corresponding values from a control site at Kaduna Polytechnic arboretum. Leaf samples were collected from five individual trees of each species from each site. Biochemical parameters used to compute APTI, including ascorbic acid content, total chlorophyll, leaf extract pH, and relative water content, were determined using standard methods. APTI was calculated using the formula: APTI equals ascorbic acid times (total chlorophyll plus pH) times relative water content divided by 10. Results showed APTI values ranging from 4.9 (Mangifera indica, sensitive) to 17.4 (Azadirachta indica, tolerant). Azadirachta indica, Eucalyptus camaldulensis, and Polyalthia longifolia had APTI values above 14, classifying them as tolerant. Ficus benjamina and Mangifera indica were sensitive, with APTI below 7. APTI declined significantly from the control site to polluted roads in all species. Azadirachta indica showed the smallest pollution-induced APTI decline (14%). The study recommends prioritising tolerant species, particularly Azadirachta indica and Eucalyptus camaldulensis, in the Kaduna State Urban Development Authority's roadside planting programme.

Keywords: air pollution tolerance index, roadside trees, urban greening, Kaduna metropolis, Azadirachta indica