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Precipitable water vapor (PWV) is an important climate parameter indicative of available moisture in the atmosphere; it is also an important greenhouse gas. Observations of precipitable water vapor in sub-Sahel West Africa are almost non-existent. Several Aerosol Robotic Network (AERONET) sites have been established across West Africa, and observations from four of them, namely, Ilorin (4.34° E, 8.32° N), Cinzana (5.93° W, 13.28° N), Banizoumbou (2.67° E, 13.54° N) and Dakar (16.96° W, 14.39° N) are being used in this study. Data spanning the period from 2004 to 2014 have been selected; they include conventional humidity parameters, remotely sensed aerosol and precipitable water information and numerical model outputs. Since in Africa, only conventional information on humidity parameters is available, it is important to utilize the unique observations from the AERONET network to calibrate empirical formulas frequently used to estimate precipitable water vapor from humidity measurements. An empirical formula of the form PWV=aTd+b where Td is the surface dew point temperature, a and b are constants, was fitted to the data and is proposed as applicable to the climatic condition of the sub-Sahel. Moreover, we have also used the AERONET information to evaluate the capabilities of well-established numerical weather prediction (NWP) models such as ERA Interim Reanalysis, NCEP-DOE Reanalysis II and NCEP-CFSR, to estimate precipitable water vapor in the sub-Sahel West Africa; it was found that the models tend to overestimate the amount of precipitable water at the selected sites by about 25 %.

ABSTRACT:The period of Harmattan season in Nigeria occurs between the month November and March, this is characterized by dry and dusty north easterly trade wind which blows from the Sahara Desert over Nigeria. Samples of the dust were collected at Iwo (7º 63'N, 4º 19'E) and Oyo (8º 12'N, 3º 42'E). The samples were analysed using AAS (Atomic Absorption Spectroscopy) machine located at Bowen University Iwo. It was observed that the sample of dust particle collected by the means of distilled water in Iwo town contains Ca (22.278ppm), Mg (8.904ppm), and Fe (2.133ppm), and the sample of dust particle collected by the means of the first rain water of the year under consideration contains Ca (5.494ppm), Mg (6.417ppm), and Fe (0.741ppm). For Oyo location, it was observed that the sample of dust particle which was collected by the means of distilled water contains Ca (17.701ppm), Mg (11.751ppm), and Fe (3.729ppm).More so, the sample of dust particle collected by the means of rain water for Oyo contains Ca (4.138ppm), Mg (4.074ppm), and Fe (0.412ppm). The results showed that there was less effect of harmattan dust on human health due to zero or no lead (Pb) content present in the same collected during the period.

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