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Tropospheric reactive bromine (Bry) influences the oxidation capacity of the atmosphere by acting as a sink for ozone and nitrogen oxides. Aerosol acidity plays a crucial role in Bry abundances through acid‐catalyzed debromination from sea‐salt‐aerosol, the largest global source. Bromine concentrations in a Russian Arctic ice‐core, Akademii Nauk, show a 3.5‐fold increase from pre‐industrial (PI) to the 1970s (peak acidity, PA), and decreased by half to 1999 (present day, PD). Ice‐core acidity mirrors this trend, showing robust correlation with bromine, especially after 1940 (r = 0.9). Model simulations considering anthropogenic emission changes alone show that atmospheric acidity is the main driver of Bry changes, consistent with the observed relationship between acidity and bromine. The influence of atmospheric acidity on Bry should be considered in interpretation of ice‐core bromine trends. Plain Language Summary: Reactive bromine in the air impacts major oxidants in our atmosphere, which remove pollutants and greenhouse gases and has changed over time in the Russian Arctic. Ice‐core bromine and acidity show a significant increase from pre‐industrial to the 1970s followed by a decrease. Our study suggests that human activities caused changes in bromine through the emissions of acidic gases from fossil fuel combustion. Considering relationships between atmospheric acidity and bromine is crucial to interpreting bromine variations in ice cores. Key Points: Bromine (Br) concentrations increased 3.5‐fold from pre‐industrial to 1975 and declined 50% by 1999 in a Russian Arctic ice‐coreA robust correlation between ice‐core Br and acidity highlights acidity's key role in influencing the atmospheric Br budgetModel shows acid‐catalyzed sea‐salt debromination is the largest source of reactive Br and drives ice‐core Br trends [ABSTRACT FROM AUTHOR]

Abstract Tropospheric reactive bromine (Bry) influences the oxidation capacity of the atmosphere by acting as a sink for ozone and nitrogen oxides. Aerosol acidity plays a crucial role in Bry abundances through acid‐catalyzed debromination from sea‐salt‐aerosol, the largest global source. Bromine concentrations in a Russian Arctic ice‐core, Akademii Nauk, show a 3.5‐fold increase from pre‐industrial (PI) to the 1970s (peak acidity, PA), and decreased by half to 1999 (present day, PD). Ice‐core acidity mirrors this trend, showing robust correlation with bromine, especially after 1940 (r = 0.9). Model simulations considering anthropogenic emission changes alone show that atmospheric acidity is the main driver of Bry changes, consistent with the observed relationship between acidity and bromine. The influence of atmospheric acidity on Bry should be considered in interpretation of ice‐core bromine trends.