The absorption coefficient of dry air at atmospheric pressure is \kappa = 0.88 \times 10ā6 mā1 in the middle of the visible band1 and the number density of air particles is given by the barometric equation : n = n0 exp(ā mgh/kT ), where n0 is the number density at sea level, m the particle mass, g the acceleration due to gravity and h the height. Assuming \kappa ā n and a constant temperature of 0ā¦C and stating any other assumptions,
(c) What is the approximate absorption cross-section of a visible photon in dry air at sea level.