Seasonal Variation, Pollution Indices and Trajectory Modeling of Bio-monitored Airborne Particulate Around Two Smelting Factories in Osun State, Nigeria

Abstract

This study determined the seasonal variation of the elemental contents of airborne particulates in the exposed lichen and moss samples, estimated the pollution status and established the air mass trajectories of the airborne particulates around two smelting factories in Osun State, Nigeria. The exposed lichen and moss samples were analyzed for elemental contents, employing X-ray fluorescence (XRF) technique. The pollution status was estimated using various indices: pollution load factor (PLF), degree of pollution load factor (DPLF), pollution load index (PLI) and relative accumulation factor, and the trajectories of pollutants were modeled using hybrid single-particle lagrangian integrated trajectory (HYSPLIT 4.0). The average concentrations of Ca and Fe were above 1000 μgg−1 showing their affinity and natural abundance in moss and lichen bio-monitors. Elements such as V, Cr, Co Ni Sr and Rb were below 100 μgg−1 in both seasons for the two sites. The elemental concentrations of moss and lichen samples, for most of the elements, were similar in trend for both sites due to similar production processes. The PLF values of Sc, Cr and Cu, Zn, Ni and Mn and Fe, Rb and Se were > 6, 3 ≤ PLF < 6 and 1 ≤ PLF < 3 for lichen and moss in both seasons and sites. The dry and wet seasonal values of the degree of pollution load factors (DPLF) are 112 and 122 for lichen and 89 and 104 for moss in Ile-Ife site; while, respectively, observed to be 90 and 113 and 93 and 97 for Ikirun site. These values showed very high degree of contamination conditions. The PLI for all the sites and seasons was above 3, indicating a progressive deterioration of the ambient air conditions of the study areas. The RAF values of Sc, Cr, Mn, Co, Ni and Cu were greater than unity, signifying accumulation property and preferential absorption from the deposited airborne particulates on the exposed lichen and moss. The backward trajectories showed arrival of air masses transport from the southwest direction, while forward trajectories showed air masses transport in northeast directions. The trajectory analysis indicates that pollutants contribution were from nearby sources with all season dispersion mostly in the southwestern parts of the smelting factories.