Effect of stratospheric O3 depletion on tropospheric SO2 column in Antarctica

When ozone is depleted in the stratosphere during ozone-hole period, UV-B radiation, which is normally absorbed in this region, penetrates into the troposphere. As a result, the behavior of several species in the troposphere, which interact with UV-B radiation, is likely to change. Sulfur dioxide is predominantly found in the troposphere. To study the behavior of sulfur dioxide during this event, a Brewer spectrophotometer was installed at Maitri (70.7°S, 11.7°E) in Antarctica in July 1999. With this instrument, the vertical column density of SO2 was measured from September 1999 to December 2003. We have observed an increase in SO2 column density during an ozone-hole event. The magnitude of increase is different in different years, on average, by a factor of ∼5 (from ∼0.5 to ∼2.5 DU). Simultaneously, the maximum value of UV-B flux at the ground was also measured. We have observed that during the ozone-hole period, the UV-B flux also increased by different amounts during different years, by a factor of ∼3-5. Good correlation has been found between SO2 column and UV-B flux but no correlation has been found between O3 column and UV-B flux from the middle of September to the middle of November. Using a simple steady-state chemical reaction scheme, an attempt has been made to examine whether the increase in UV-B flux could increase the SO2 column during the ozone-hole period.