Transport of very short-lived substances from the Indian Ocean to the stratosphere through the Asian monsoon

• Main Author: Fiehn, Alina
• Format: Thesis
• Language: English
• Published: 2017
• Subjects: Indian; Pacific; Antarc*; Antarctica
• Online Access: https://oceanrep.geomar.de/id/eprint/41781/; https://oceanrep.geomar.de/id/eprint/41781/1/DoktorarbeitAlinaFiehn.pdf

Anthropogenic halogenated substances cause the ozone hole above Antarctica through catalytic ozone destruction and depletion of the stratospheric ozone layer, which shields the Earth from harmful ultraviolet radiation. Their emissions were regulated through the Montreal Protocol in 1989. Since the beginning of the 21st century, the amount of chlorine and bromine in the stratosphere from long-lived ozone depleting substances (ODS) has been decreasing and stratospheric ozone has started to increase slowly. Under these circumstances the importance of natural halogenated substances for atmospheric composition and chemistry will increase in the future. Trace-gases with atmospheric lifetimes of less than half a year belong to the so-called very short-lived substances(VSLS). The most important bromine containing VSLS bromoform (CHBr3, 17 days lifetime) and dibromomethane (CH2Br2, 150 days) from marine sources currently contribute about 25% to the observed stratospheric bromine loading. In addition, the short-lived VSLS methyl iodide (CH3I, 3.5 days) contributes to stratospheric iodine levels. Sulfur containing compounds, such as dimethylsulfide (DMS, 1 day), also influence stratospheric ozone. Sulfur supplies the stratospheric aerosol layer, which amplifies heterogeneous chemical ozone depleting reactions under high chlorine levels. DMS is a potential source of sulfur to the stratosphere. VSLS are naturally produced in the oceans by phytoplankton, macro algae, and photochemistry. They are primarily transported to the stratosphere with deep convection in the tropics and mainly enter the stratosphere over the Pacific warm pool in boreal winter and the Asian monsoon region in boreal summer. Major uncertainties still exist with respect to the oceanic emissions of halogenated VSLS from the Indian Ocean and their stratospheric entrainment through the Asian monsoon circulation. This thesis investigates the emissions of VSLS from the Indian Ocean and their transport to the stratosphere with novel combinations of data and ...