Abstract
Abstract Extensive measurements of the thermal infrared sky radiance and the atmospheric dust concentration were obtained for a period of 2 years in Nsukka, Nigeria. The global sky radiation was monitored with a pyrgeometer while the dust concentration in the atmosphere was measured with an integrating nephelometer. Related climatological variables, e.g. partial water vapour pressure or dew-point temperature, were also recorded within the period. Analysis was made for clear sky conditions. Results show that a high level of atmospheric dust concentration during the harmattan period (November to February) strongly affects the clear sky emissivity to an extent that the sky behaves like a blackbody at ambient temperature. Based on the overall data obtained, an IR sky radiance model was developed relating the global sky emissivity to surface dew-point temperature and atmospheric dust concentration.
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