Seasonal evaluation of chemical compositions of dust fall at motor parks in a Nigerian university campus

Abstract

Bulk dust fall was collected from three different motor parks in University of Ilorin using an open-bucket sampler for 5 months of dry and wet season periods. The collected bulk dust fall was separated by filtration to obtain a filtrate and a residue. The filtrate pH and conductivity were determined as well as concentrations of $${\text{SO}}_{4}^{2 - }$$ , $${\text{NO}}_{3}^{ - }$$ and $${\text{NH}}_{4}^{ + }$$ using a Beckman UV/visible spectrometer, Cl− titrimetrically with silver nitrate while Na+ and K+ ions by flame photometer (FP 640). Atomic absorption spectrometry (Buck Scientific 210/211VGP) was used to determine Mg2+ and Ca2+ in the filtrate and heavy metals (Mn2+, Cd2+, Cu2+, Fe3+ and Zn2+) in the residue. The pH for both season periods was slightly less than 7 at all the sites except for PK2 in dry season period, while EC was higher in the dry season than in the wet season period at all sites. There were high concentrations of anions during the wet season period, but cations were more during the dry season. The abundance of parameters generally followed the order of Cl− > $${\text{NO}}_{3}^{ - }$$ > $${\text{SO}}_{4}^{2 - }$$ for anions, Na+ > $${\text{NH}}_{4}^{ + }$$ > K+ > Ca2+ > Mg2+ for cations in filtrate, while heavy metals generally followed Fe3+ > Zn2+ > Mn2+ > Cu2+ > Cd2+ in residue. The metal pollution index of residue for heavy metals showed that all the sites were polluted with heavy metals in both seasons. A very wide seasonal variation was generally observed which was due to metrological conditions and vehicular density.