Abstract

Approximately three years of sunphotometric measurements carried out in the locality of Bidi (13.36°N; 2.30°W) in Burkina Faso (West Africa) from October 1986 to January 1989 were used to estimate the atmospheric precipitable water vapour (APW) and the Angstrom exponent values a. A study of the relationship between these two parameters on a seasonal time scale shows that an increase of water vapour in the Sahel is associated with a decrease of a values, indicating  hygroscopic growth of aerosol particles. This result shows that the Sahel aerosol particles may grow in size through water vapour absorption due to hygroscopic properties.

Key words: Aerosol, optical depth, angstrom coefficient, atmospheric water content and hygroscopic growth.