A heterogeneous open ocean source for glyoxal and iodine oxide

The climate relevance of biologically active ocean upwelling regions has primarily been studied in terms of the air-sea partitioning of long-lived greenhouse gases (e.g., CO2, CH4, N2O etc), and the release of the reactive gas DMS, which can form aerosols as a result of atmospheric transformations. Considerably less attention has been paid to open ocean sources of other reactive gases that, like DMS, can form aerosols. Such molecules are glyoxal (CHOCHO) and IO. Glyoxal is an indicator for oxidative hydrocarbon chemistry, and a building block for secondary organic aerosol (SOA). SOA modifies the hygroscopic properties of organic aerosols, and potentially also adds to the growth of small particles to sizes that can more easily activate to form cloud droplets. Iodine oxide (IO) can nucleate new particles, and/or adds to the growth of pre-existing particles. Due to the very high solubility of the glyoxal molecule, concentrations in excess of 100ppt over the open ocean like we found over the Pacific Ocean require an airborne source mechanism (Sinreich et al., 2010). We have investigated the source mechanism further during a ship campaign in 2009, as well as a first research flight aboard the NSF/NCAR GV research aircraft (HIAPER). Both campaigns give clues about the sources of both gases over the remote tropical Pacific Ocean, and reveal a surprising impact on the composition of the free troposphere.