An Investigation on Effects of Harmattan Dust (aerosols) on Horizontal Visibility Deterioration over Bauchi, North- eastern Nigeria

In this paper, the effects of harmattan dust (aerosols) on visibility deterioration over Bauchi, a town in North-eastern Nigeria was investigated. The data of visibility readings for a period of ten (10) years were obtained by human identification of target objects and landmarks, most especially hills and buildings at known distances in a full 360 degrees circle around the observation point. The annual cycles of visibility in Bauchi for daily and monthly averages for ten years (1998-2007) were obtained. This enabled us to determine atmospheric extinction coefficient (βext.), which results in the scattering and absorption due to dust particles by using the Koschmieder relationship for the study area. Bauchi recorded a maximum visibility value of about 35000.0m in April/May 2005. The minimum visibility value of nearly zero was recorded on November/December 2000. However, during the months of June-September, the maximum atmospheric extinction coefficient value of 0.230 was recorded in 2007 and the minimum atmospheric extinction coefficient value of 0.164 was recorded in 1999. For the months of harmattan season (November to February), the maximum atmospheric extinction coefficient value of 0.689 was recorded in 2000/2001 and the minimum atmospheric extinction coefficient value of 0.270 was recorded in 2005/2006.

Keywords:

Visibility , Harmattan dust , Extinction coefficient , Scattering , Absorption