Reactive bromine species in the troposphere affect ozone (O 3 ) as well as the cycling and fate of hydrogen oxide (HO x ) and nitrogen oxide (NO x ) radicals, with implications for the oxidative capacity of the atmosphere, greenhouse gas budgets, air quality, and human health. However, uncertainties remain in the global distribution and chemical mechanism of inorganic bromine with few in situ observations, especially outside of polar regions. We present results of speciated gas-phase reactive bromine observations made in the Marine Boundary Layer (MBL) at a coastal site in the Northwest Atlantic Ocean during January and February 2023, as part of the Bermuda boundary Layer Experiment on the Atmospheric Chemistry of Halogens (BLEACH) campaign. Using an iodide-adduct high resolution time of flight chemical ionization mass spectrometer (HR-ToF-CIMS) equipped with a custom atmospheric pressure transverse ion–molecule reaction region (t-IMR), we observe subppt levels of atmospheric inorganic bromine compounds including Br 2, BrCl, HOBr, BrONO 2, and BrO in the marine boundary layer. To our knowledge, these are the first reported in situ observations of gaseous bromine nitrate (BrONO 2 ). An experimental calibration for hypobromous acid (HOBr) produces sensitivity values in agreement with previous studies and theoretical calculations involving binding enthalpies, which we use to convert measured ion signals to units of ambient mixing ratios. We characterize the relationship between reactive bromine levels and surrounding environmental factors including meteorological conditions, influences from local pollution sources, and “clean marine” periods of onshore winds. Measured mixing ratios for all bromine species are found to be much lower than predicted by a GEOS-Chem model simulation, which includes fully coupled reactive halogen chemistry. We discuss the implications of this discrepancy on reactive bromine sources and multiphase chemistry, highlighting the need to better constrain heterogeneous uptake rates for key species.
Rund et al. (Tue,) studied this question.