窒素同位体比からみた富山降水中の硝酸イオンの挙動

概要

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Nitrogen isotope ratio of nitrate ion in precipitation at Toyama was traced from June 2003 to December 2005 to investigate the behavior of nitrate ion inassociation with precipitation. δ^<15>N value varied from -7.8 to + 1.6%o and showed seasonal variation; i.e., it was higher in winter than in summer. δ^<15>N value negatively correlated to solar radiation. Negative correlation was also observed between δ^<15>N value and concentration of atmospheric oxidant, which converted NO_2 to HNO_3. Such correlations suggest that the δ^<15>N value of nitrate ion decreases with increasing conversion rate from atmospheric NO_2 to HNO_3. Based on an equation obtained from the relationship between the conversion rate and δ^<15>N value according to the Rayleigh distillation model, 78-98% (av. ±1σ, 90±5%) NO_2 exhausted into the atmosphere were estimated to be converted into HNO_3. The similar seasonal variation was also observed at Nagoya, although the δ^<15>N values are systematically higher than those of Toyama. The NO_2 concentration at Nagoya istwice as high as the concentration at Toyama, suggesting that the conversion rate from NO_2 to HNO_3 is lower in Nagoya (av. ±1σ, 86±6%) than in Toyama.
日本地球化学会の論文
2008-03-20