Graduate seminar by Carlos J. Valle Diaz, UPRRP, Department of Chemistry

Title:
Tropospheric Ozone Depletion Events in Polar Regions – A Closer Look to the Bromine Explosion Mechanism

Abstract:
In the polar spring over the Arctic and the Antarctica regions, halide salt ions are converted into reactive halogen species that drastically deplete ozone concentrations in the troposphere. After an anti-correlation of O3 and bromine was discovered in the 1980s, research on ozone depletion events (ODEs) has shown the central role of halogen photochemistry in Polar Regions. Surface-air exchange processes are believed to be source of the halogen radicals that promote ODEs. However, a comprehensive mechanism of how salts are transported from the ocean and oxidized to become reactive halogen species in the air is still under speculation. The termination of ODEs is driven mainly by meteorological processes and control by surrounding topography. Removal of tropospheric ozone generates reactive halogen atoms and their oxides that become the primary oxidizing species. Removing the primary oxidizing species of the Polar Regions poses a potentially serious imbalance in the environment and climate. Environmental consequences of ODEs include removal of gaseous mercury that becomes bio-available in the polar ecosystem, alteration of oxidation fates for organic gases, export of bromine into the free troposphere, and impact in ice core chemistry. Recent changes in the Arctic sea ice cover due to climate change are likely to alter the occurrence and intensity of ODEs. In this seminar, the history of the discovery of ODEs, the techniques used to measure them, what it is known of this surface-air exchange atmospheric photochemical process, and the present challenges to be addressed will be discussed.