Consider the absorption of 240 nm sunlight by O₂. The O₂ cross section at this wavelength is 10^-24 cm² molecule^-1. Assuming that F_TOA photons of this wavelength enter the top of the atmosphere, derive the equation for the attenuation of this light as a result of absorption of these photons as a function of altitude, neglecting scattering, for a solar zenith angle of 0 degrees. You may assume n_air(0) = 2.6 x 10¹⁹ molecules cm^-3 and the atmosphere scale height H = 7.4 km. As the sun moves lower in the sky, how does the absorption change?