Shaddy Ahmed

and 15 more

Reactive chlorine and bromine species emitted from snow and aerosols can significantly alter the oxidative capacity of the polar boundary layer. However, halogen production mechanisms from snow remain highly uncertain, making it difficult for most models to include descriptions of halogen snow emissions and to understand the impact on atmospheric chemistry. We investigate the influence of Arctic halogen emissions from snow on boundary layer oxidation processes using a one-dimensional atmospheric chemistry and transport model (PACT-1D). To understand the combined impact of snow emissions and boundary layer dynamics on atmospheric chemistry, we model \ch{Cl2} and \ch{Br2} primary emissions from snow and include heterogeneous recycling of halogens on both snow and aerosols. We focus on a two-day case study from the 2009 Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) campaign at Utqia\.gvik, Alaska. The model reproduces both the diurnal cycle and high quantity of \ch{Cl2} observed, along with the measured concentrations of \ch{Br2}, \ch{BrO}, and \ch{HOBr}. Due to the combined effects of emissions, recycling, vertical mixing, and atmospheric chemistry, reactive chlorine is confined to the lowest 15 m of the atmosphere, while bromine impacts chemistry up to the boundary layer height. Upon including halogen emissions and recycling, the concentration of \ch{HO_x} (\ch{HO_x} = \ch{OH}+\ch{HO2}) at the surface increases by as much as a factor of 30 at mid-day. The change in \ch{HO_x} due to halogen chemistry, as well as chlorine atoms derived from snow emissions, significantly reduce volatile organic compound (VOC) lifetimes within a shallow layer near the surface.