Halogen activation from the interaction of N2O5 with sea salt in the marine boundary layer during TexAQS-GoMACCS 2006

The nitrate radical, NO3, formed from reaction of NO2 with O3, and dinitrogen pentoxide, N2O5, formed from subsequent reaction of NO3 with NO2, drive several important chemical processes, including oxidation of VOCs (by NO3) and removal of NOx (= NO + NO2) by the heterogeneous reaction of N2O5 to form either nitric acid, HNO3, and/or aerosol nitrates. Laboratory studies have shown that heterogeneous uptake of N2O5 on sea salt aerosol produces nitryl chloride, ClNO2. Photolysis of ClNO2 is believed to be a potential source of Cl atoms, an important oxidant of VOCs in the marine boundary layer. In spite of the potential importance of this halogen activation mechanism, field investigations have yet to directly confirm it. We have measured NO3 and N2O5, by cavity ring-down spectroscopy, and observed ClNO2, by I- chemical ionization mass spectrometry, on board the NOAA research vessel Ronald H. Brown during the Texas Air Quality Study - Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006. In this presentation, we highlight a few aspects of the interaction between nitrogen oxide and halogen cycles in the subtropical marine boundary layer, including ClNO2 production from N2O5 uptake on sea salt aerosol and ClNO2 removal via deposition and photolysis.