Actinic radiation in the terrestrial atmosphere

Actinic radiation originating from the Sun drives the photochemistry of the Earth's atmosphere. Surprisingly few measurements have been made of this terrestrial forcing agent which is responsible for such anthropogenically critical issues as the production and loss of atmospheric ozone. This paper describes the status of our knowledge of actinic radiation throughout the middle and lower atmosphere with the goal of summarizing progress to date and identifying future requirements. The focus is mainly on radiation, with wavelengths between 170 and 400 nm, but does include other UV radiation which is deposited in the middle atmosphere. Topics are covered in their natural order, beginning with the solar spectral irradiance above the atmosphere, its transmission through the atmosphere, the component which is multiply scattered, UV radiation reaching the biosphere, and direct measurements of photolysis rates. Concluding remarks include recommendations for additional research. Published by Elsevier Science Ltd.