Temporal-spatial variability of seasonal aerosol index and visibility — A case study of Nigeria

A long-term (1984-2013) aerosol index observation derived from Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI) as well as meteorological parameters are analyzed focusing on Nigeria. The results show that, the pattern of distribution and variability of aerosol index (dust concentration) is not uniform over Nigeria. Rather depends strongly and significantly on latitude and season both temporally and spatially. The overall mean over 30-years has shown high values in northern Nigeria compared to the south, with spatially distributed average ranging from 1.5 to 1.9 in the desert dust dominated zones (Sahel and north central). While lower values (1.1-1.4) are observed in the southern zones with annual mean variability showing the higher tendency to increase year by year in this zones. AI values were found to be high in harmattan season with significant spatial density as indicated by AI greater than 1.5 throughout Nigeria except in the mountainous area of Jos. These signified the influence of transported dust over all the region. During harmattan, the peak values and variability of AI appears in the south and decreases with increasing latitude while opposite occur during the summer. The variability in AI values has caused a great impact on visibility and temperature as both drastically drop to the lowest values during harmattan. The trend of AI is found to increase with time while visibility exhibited a decreasing trend from 1984-2013.