New insights in the global cycle of acetonitrile: release from the ocean and acetonitrile: release from the ocean and Venezuela

Abstract

Using the proton transfer reaction mass spectrometry (PTR-MS) technique,acetonitrile was measured during the wet season in a Venezuelan woodlandsavanna. The site was located downwind of the Caribbean Sea and nobiomass burning events were observed in the region. High boundary layerconcentrations of 211+/-36 pmol/mol (median, +/- standard deviation)were observed during daytime in the well mixed boundary layer, which isabout 60 pmol/mol above background concentrations recently measured overthe Mediterranean Sea and the Pacific Ocean. Most likely acetonitrile isreleased from the warm waters of the Caribbean Sea thereby enhancingmixing ratios over Venezuela. Acetonitrile concentrations will probablystill be much higher in biomass burning plumes, however, the generalsuitability of acetonitrile as a biomass burning marker should betreated with care.During nights, acetonitrile dropped to levels typically around 120pmol/mol, which is consistent with a dry deposition velocity of similarto0.14 cm/s when a nocturnal boundary layer height of 100 m is assumed.