Jornal da Poluição

Variability of Harmattan Dust Haze Over Northern Nigeria

Abstract

Michael Chukwuemeka Ochei and Emmanuel Adenola

The spatial and temporal variability, trend of visibility, frequency of occurrence (FOO) of ‘thick dust haze’ (TDH) and of ‘light dust haze’ (LDH) during the Harmattan season (November to February) were examined, using 27-year visibility data for 8 synoptic stations located in northern Nigeria. Visibility target used to differentiate TDH and LDH occurrence is that when visibility ≤ 1,000 m (Vx ≤ 1,000 m), which indicates Thick Dust Haze (TDH); while visibility range of ˃1,000 m and ≤ 5,000 m (1,000 m ˂ Vx ≤ 5,000 m) indicates Light Dust haze (LDH). The visibility pattern showed a decreasing trend throughout the study period as lowest visibility was observed in the month of January. Highest FOO of TDH and LDH conditions were also observed in this month, identifying January as the month of poorest visibility conditions and high occurrence of dust haze. The average frequency of TDH days observed was about 2– 4 days and LDH days from 2 – 11 days. The FOO of LDH days increases southwards which could be attributed to the predominance of fine dust particles and lower wind speed towards the south. TDH days follows a decreasing trend all through the study period, while LDH follows an increasing trend. TDH and LDH occurrences showed an inverse in relationship with respect to latitude. Visibility deterioration during the harmattan period is largely caused by the prevalence of dust particles in the atmosphere.