Abstract
Using a number of datasets from single particle Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS) measurements, we show only a minor presence of Organic Nitrogen (ON) species in Saharan dust particles (aerosol size range 0.2-3 mu m) collected at their origin. ON enhancement is not observed on Saharan dust particles after atmospheric transport (48-96 h) either over the Tropical Ocean in the vicinity of Cape Verde, over the North Atlantic Ocean. In the negative ATOFMS mass spectra, signals due to ON species were found weaks in biological particles (rich in potassium and phosphate) in their source area, and signals due to alkylamines in the positive ATOFMS mass spectra were not found. In striking contrast, biological particles travelling within aerosol dust plumes are found to be enriched in ON species - including alkylamines - in North Atlantic Ocean air (Mace Head, Ireland), as seen in both positive and negative ATOFMS mass spectra. Contrary to filter based aerosol techniques which report ON enrichment within Saharan dust, our single particle mass spectrometry data - allowing study of the aerosol mixing state - suggests that the aging biological particles and not the associated transported aging Saharan dust may be a source of ON species. We suggest biogeochemical processes occurring in the atmosphere In which biological particles are responsible for ON production. This may be an important source of nutrients to the ocean via atmospheric deposition.