Aerosol isotopic ammonium signatures over the remote Atlantic Ocean

- Aerosol NH4 δ15N measurements with improved sensitivity are reported, confirming a global isotopic distribution pattern.
- Pattern of isotopic signals may be either mixing between two end members or fractionation during aerosol transport.

We report aerosol ammonium 15N signatures for samples collected from research cruises on the South Atlantic and Caribbean using a new high sensitivity method. We confirm a pattern of isotopic signals from generally light (δ15N −5 to −10‰), for aerosols with very low (<2  nmol m−3) ammonium concentrations from the remote high latitude ocean, to generally heavier values (δ15N +5 to +10‰), for aerosols collected in temperate and tropical latitudes and with higher ammonium concentrations (>2  nmol m−3). We discuss whether this reflects a mixing of aerosols from two end-members (polluted continental and remote marine emissions), or isotopic fractionation during aerosol transport.