The thickness of Earth?s ozone layer at any location is measured in Dobson Units (DU), where 1 DU corresponds to a gas layer of thickness 10 ?m if the gas pressure were raised to 1 atm. Show that 1 DU corresponds to 2.69 ? 10¹⁶ molecules/cm². Data on the absorption cross section for ozone are given in Figure 23.13

Normally the thickness of the ozone layer is ? 300 DU, but due to ozone destruction by chlorofluorocarbons it had dropped as low as ? 90 DU over Antarctica during the 1990 s. How low would the ozone level have to drop to allow 10^?6 of the incident UV flux at ? ? 250 nm or 220 nm to reach sea level? (You will need to use the result of Problem 23.5.)

Transcribed Image Text:

12.5 10 7.5 5- 2.5- 250 wavelength [nm] 220 280 absorption cross section cm²/molecule] 18