Chemistry-climate modelling of polar bromine chemistry and its interaction with the cryosphere (BromoPole)

• Applicant: Privatdozent Dr. Björn-Martin Sinnhuber
• Subject Area: Atmospheric Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517648310

The BromoPole project aims at improving our understanding of the mechanisms of polar bromine explosion and ozone depletion events and their impact on the larger scale through global chemistry climate model simulations. Tropospheric ozone is after carbon dioxide and methane the most important greenhouse gas and affects air quality with implications for health and eco systems. During spring-time in the polar regions of both hemispheres tropospheric ozone depletion events with near complete removal of boundary layer ozone are frequently observed. These ozone depletion events are caused by so-called bromine explosion events, that can be observed as strongly enhanced tropospheric bromine monoxide (BrO) columns. Although the polar spring-time ozone depletion and bromine explosion events have been studied now for more than three decades and important progress in understanding their mechanisms has been made, many aspects still remain unclear. There is still no generally accepted comprehensive mechanism, and consequently most chemistry climate models do not include mechanisms of polar tropospheric bromine chemistry. This limits our knowledge of the larger scale impacts of bromine explosion events on tropospheric ozone and on the long-term changes in a changing climate. Within the BromoPole project we will perform simulations with the chemistry climate model EMAC, building on our previous work with this model system. In particular, we will test a new hypothesis that accumulated bromine deposition from the gas phase onto the snow surface may play an important role for bromine explosion events. Comparison of the model simulations with satellite BrO observations will be used to examine how well the timing and distribution of bromine explosion events can be reproduced in the model by this new mechanism, taking into account the accumulated deposition from the gas phase. New analyses of a long-term Arctic data set of bromide in surface snow samples taken in Ny-Alesund, Spitsbergen, together with planned additional snow samples, will help to better understand the interaction of atmospheric bromine chemistry with the cryosphere. With this improved process understanding we will then perform model simulations to investigate the impact of polar bromine chemistry on tropospheric ozone and the oxidizing capacity of the atmosphere on the regional to global scale as well as possible long-term changes in a changing climate.

• DFG Programme: Research Grants