Seasonal variation in atmospheric deposition of nitrate, sulphate, lead, zinc, and copper in southwestern Nigeria

Atmospheric and soil levels of nitrate-nitrogen (NO3-N), sulphate (SO,), lead (Pb), zinc (Zn), and copper (Cu) in southwestern Nigeria were determined. Rainfall and dust samples were collected at 2-week intervals and after a major rainfall and dust storm events at eight locations in a transect from the coast in Badagry to Ilorin, 300 km from the coast. The parameters were evaluated on monthly, seasonal, and annual bases for 2 years. The pH of the deposited materials varied with season and distance from the coast. Higher values were obtained in the dry season and in the hinterland. Soil pH followed a similar trend. The average annual depositions of NO3-N, SO4, Ph, Zn, and Cu ranged from 4.05 to 6.60, 2.58-5.85, 0.60-2.76, 0.96-2.52, and 0.39-2.79 kg ha(-1), respectively. Correspondingly the values in soil ranged from 7.45 to 15.65, 3.15-9.50, 1.65-3.35, 1.65-2.80, and 1.75-3.70 kg ha(-1). The values also varied with season. Relationships between deposited ph and Cu and soil values were significant. It was: concluded that harmattan dust and/or motorized traffic do contribute significantly to the soil levels of Pb and Cu and less significantly to the levels of pH, NO3-N, SO4, and Zn in the soil.