Polar regions are highly sensitive to climate change. Rising temperatures and sea ice loss are changing the environment and affecting atmospheric chemistry. Tropospheric bromine monoxide (BrO) is a key species involved in springtime Arctic ozone depletion. It is thought to originate from sea-ice snowpacks, blowing snow, and sea salt aerosols. Due to limited long-term observations, its sources and processes are not fully understood.

In a study published in Atmospheric Chemistry and Physics, researchers from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences, along with the collaborators from the British Antarctic Survey and the University of Bremen, systematically investigated the sources of reactive bromine in the Arctic troposphere and their impact on atmospheric oxidative capacity in polar regions.

Using a multi-axis differential optical absorption spectroscopy system independently developed by HFIPS, researchers carried out more than ten years of observations at the Chinese Arctic Yellow River Station. Long-term records of tropospheric BrO and aerosol extinction profiles helped improve the performance of chemical transport models in simulating reactive bromine and ozone.

Using the p-TOMCAT chemical transport model, researchers successfully reproduced the Arctic springtime bromine explosion events and ozone depletion episodes, suggesting that the reactive bromine sources had been underestimated.

Researchers showed that the blowing snow over sea ice played a major role in releasing reactive bromine, while recycling processes on sea salt aerosol surfaces helped maintain high BrO levels in the Arctic troposphere. Source analysis revealed that the blowing snow over multi-year sea ice contributed more than 50% of the bromine emissions associated with total sea ice, a contribution comparable to that from first-year sea ice.

"These findings show that multi-year sea ice plays a key role in Arctic bromine explosions, and this study gives us new insights into how reactive bromine behaves in the Arctic atmosphere," said Prof. LUO Yuhan, one corresponding author of the study.