SPECTRAL MEASUREMENTS OF VISIBLE SOLAR DIRECT-NORMAL IRRADIANCE AND AIR POLLUTANT ATTENUATION COEFFICIENTS AT HELWAN

Solar radiation spectra were measured by a ground-level pyrheliometer (Eppley NIP) equipped with a filter wheel. Three flat, circular, Schot t fillers were used to define three spectral bands. The filters were l arge band-pass filters of the types OG530, RG630 and RG695. The experi ment was conducted from June 1991 to May 1992 on the roof of the new b uilding of the National Research Institute of Astronomy and Geophysics (NRIAG) at Helwan. The Linke turbidity factor for the integrated radi ation, and the spectral attentuation coefficients of solar energy caus ed by aerosols were computed. In comparison with earlier measurements in 1910, 1967 and 1987, it is clear that there is a continuous increas e in the turbidity factor, due to an increase of industrial waste in t he Helwan atmosphere. A correlation analysis between the turbidity fac tors and the total suspended particles, smoke and sulphur dioxide was carried out. Meteorological elements and sand storms have been taken i nto consideration in the correlation analysis.