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Atmospheric Aerosol Loading at Ilorin, a Tropical Station
(The African Review of Physics, 2014) Willoughby, Alexander
This work reports the inter-annual variability of the seasonally recurring aerosol haze at Ilorin (8°32¢N, 4°34¢E) a central state of Nigeria, which is in the tropical zone. The data consist of observations collected over a period of seven years 1987 –1990 and 1996 - 1998 using the EKO Sun-photometer model SM –120 with “peak hold” and full view 2.4°quartz window and interference filters having peak transmission at the wavelengths 500, 675, 875 and 945nm, respectively. The data coverage presents to us five distinct aerosol seasons viz: 1987/88, 1988/89, 1989/90, 1996/97 and 1997/98. The data collected for all the aerosol seasons were compared wavelength-by-wavelength and month-by-month. Although the regional mean Aerosol Optical Depth (AOD) and Precipitable Water (PW) remains essentially constant in trend for all the data years, they vary from year to year with spread ranging from 0.789 to 1.526 for AOD1, 0.808 to 1.50 for AOD2, 0.814 to 1.178 for AOD3, and 0.340 to 1.480 for the PW. The coefficient of variation determined is between 27.4 and 52.0 for AOD1, 23.9 and 53.2 for AOD2, 25.2 and 52.8 for AOD3 and 12.9 and 39.5 for PW. The Angstrom exponent was also found to vary from about 0.2 to 3.8.