1. Definition of Dobson unit 1 Dobson Unit (DU) is defined to be 0.01 mm thickness at standard temperature and pressure (STP) How many molecules are in a column with area 1 cm 2 and containing 300 DU of ozone? k is Boltzmann’s constant = 1.3806505(24) × 10 −23 J K−1 T is 273 K P=1 atm=1013.25 mbar=101325 Pa A=1cm 2 =10 -4 m 2 h=height of ozone column at STP=3 mm

2. Spectra calculations Spectral global Irradiance in W/m 2 /nm Spec1 Spec2 Calculate : Total integrated UV irradiance UVA irradiance UVB irradiance UV Index

3.  Airmass for spherical atmosphere The airmass for a plane parallel atmosphere is m=1/cos  0 In reality, the Earth atmosphere is curved. R h The airmass m = 1/cos  m 00 Calculate the airmass for a solar angle  0 =75º and 85 º at a height of 22 km and 5 km and compare it to the plane parallel case.