The loss in the received amounts of normal incidence solar radiation at the ground level at noon time reaches 47% of that incident outside the earth's atmosphere. The corresponding depletion figures in the amount of direct radiation received in the studied spectral band were 33% in the band less than 530 m mu, 50% in the visible range (530 < < 695 m) and 46% in the infrared range (lambda > 695 m mu) of the solar spectrum. The fractions of the spectral bands to the normal incidence solar radiation at the ground level are in the yearly average 30%, 20% and 49% for the above mentioned spectral bands, respectively. The extinction coefficient for normal incidence solar radiation range was 0.36-0.60 with a mean value of 0.50, Approximately, a similar trend occurs for the energy in the visible and in the infrared ranges of the solar spectrum. Extinction below 530 m mu was found to vary over 0.23-0.41 with smaller values occurring during the warmer months. (C) 2001 Elsevier Science Ltd. All rights reserved.