Ozone stratosphere was discovered to be declining, mostly because of increasing concentrations of chlorofluorocarbons (CFC) and similar chlorinated and brominated organic molecules. The concern over the health effects of the decline led to the 1987 Montreal Protocol, the ban on the production of many ozone depleting chemicals and in the first and second decade of the 21st Century the beginning of the recovery of stratospheric ozone concentrations. Ozone in the ozone layer filters out sunlight wavelengths from about 200 nm UV rays to 315 nm, with ozone peak absorption at about 250 nm. This ozone UV absorption is important to life,
Computation of radiowave attenuation in the atmosphere recommendations is available for download and is available to the public. The document ITU-R P.676-8 of the ITU-R section considers the atmosphere as being divided into spherical homogeneous layers; each layer has a constant refraction index. By the use of trigonometry, a couple of formulas and an algorithm were derived. Through the use of an invariant, the same results can be directly derived: An incident ray at A under the angle Φ hits the layer B at the angle "θ". From basic Euclidean geometry: By Snell's law: so that Notes: The ITU recommended algorithm consists of launching a ray from