A Stable Isotope Investigation of Precipitation Nitrate
Cooney, Katherine Suzanne
MetadataПоказать полную информацию
The isotopic composition of precipitation nitrate reflects the processes involved in its formation. Silver nitrates prepared from Maryland precipitation were thermally decomposed to gases for mass spectrometric analyses. Nitrate &#948;15N ranged from -5.1±0.5 to +5.9±0.5 (1&#963;), &#948;18O ranged from +42.6±0.5 to +81.9±0.5, and &#916;17O ranged from +15.33±0.05 to +31.71±0.05. Precipitation samples were re-analyzed for &#948;15N and &#948;18O using a method in which bacteria convert nitrate to N2O for analyses, and d15N ranged from -3.6±0.2 to +7.1±0.2 and &#948;18O ranged from +61.6±0.3 to +86.8±0.3. Differences between the methods were attributed to organic contaminants in the silver nitrates. Nitrate &#948;15N, &#948;18O, and &#916;17O were highest in the winter and lowest in the summer. Ion concentrations, storm track data, and the &#948;34S of precipitation sulfate were used for interpretations. Most likely, &#948;15N varied due to seasonal changes in the NOx photo-stationary state, and &#948;18O and &#916;17O varied due to changes in oxidation chemistry.