Major influence of BrO on the NO_x and nitrate budgets in the Arctic spring, inferred from Δ¹⁷O(NO₃^–) measurements during ozone depletion events

Abstract : The triple oxygen isotopic composition of atmospheric inorganic nitrate was measured in samples collected in the Arctic in springtime at Alert, Nunavut and Barrow, Alaska. The isotope anomaly of nitrate (Δ¹⁷O = δ¹⁷O – 0.52δ¹⁸O) was used to probe the influence of ozone (O3), bromine oxide (BrO), and peroxy radicals (RO₂) in the oxidation of NO to NO₂, and to identify the dominant pathway that leads to the production of atmospheric nitrate. Isotopic measurements confirm that the hydrolysis of bromine nitrate (BrONO₂) is a major source of nitrate in the context of ozone depletion events (ODEs), when brominated compounds primarily originating from sea salt catalytically destroy boundary layer ozone. They also show a case when BrO is the main oxidant of NO into NO₂.