During the Southern Hemispheric spring of 2000 (during the months of November and early December), rain, bulk and size-separated aerosol samples were collected at the Cape Grim Baseline Air Pollution Station located on the island of Tasmania, Australia and analyzed for total organic nitrogen (N), urea, and dissolved free amino acids. Rain and bulk aerosol samples contained organic N at concentrations representing, on average, between 19 and 25% of total N. Urea was not detected in the six rain samples analyzed. However, urea represented ∼24% of the organic N contained in nonbaseline aerosol samples, and ∼2% of the organic N contained within baseline samples. Trajectory analysis combined with meteorological data indicated that high concentrations of urea within aerosols were mainly due to Tasmanian sources, likely animal emissions, although the application of urea fertilizers cannot be dismissed as a source. In nonbaseline samples the highest concentrations of urea were associated with the coarse mode aerosol (greater than 1 μm), although urea was also found in the fine mode aerosol (less than 1 μm), potentially indicating gas-to-particle conversion of urea. Aerosol samples collected in marine air masses contained urea within an intermediate fraction centered at ∼1 μm suggesting the sea surface microlayer as a source. Dissolved free amino acids contributed ∼53% of the organic N in rain, but were not a significant proportion of the total organic N fraction in either nonbaseline or baseline aerosol samples. Due to their presence in rain, amino acids likely exist in aerosols as unhydrolyzed proteins. In cascade impactor samples highly influenced by marine sources, profiles for amino N were inversely related to urea N, possibly indicating live species and the sea surface microlayer as a source for organic N.
Relation
Journal of Geophysical Research / Vol. 108, no. D11
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