[AAS07-P29] Five-years seasonal variations of nitrogen and triple oxygen isotopic compositions of atmospheric nitrate at Noto Peninsula, Japan
Keywords:Nitrate, Aerosol, Triple oxygen isotopes, Nitrogen isotope ratio
The nitrogen and triple oxygen isotopic compositions (δ15N and Δ17O = δ17O − 0.52 × δ18O) of atmospheric nitrate can be a tracer of the sources and formation pathways of atmospheric nitrate. The δ15N of atmospheric nitrate can be used to estimate the sources and sinks of atmospheric nitrate. The Δ17O of atmospheric nitrate can be a tracer of the relative importance of mass-independent oxygen-bearing species (e.g. O3, BrO; Δ17O ≠ 0 ‰) and mass-dependent oxygen-bearing species (e.g. OH radical; Δ17O ≈ 0 ‰) during the conversion of NOx to atmospheric HNO3. In this study, we present five-years data of δ15N and Δ17O values in atmospheric nitrate collected at NOTO Ground-based Research Observatory (NOTOGRO) (37.5°N, 137.4°E) located at the north coast of Noto Peninsula, Japan.
The atmospheric nitrate concentrations did not show a clear trend, while the δ15N and Δ17O showed a clear seasonal variation with summer minimum and winter maximum. The trend of Δ17O is caused by the seasonal changes in the O3 / HOx ratios decreasing in summer by ozone destruction and HOX production (e.g. OH, HO2 radicals) via UV irradiance. Although the correlation between δ18O and Δ17O values was observed throughout the year, the slope between δ18O and Δ17O values for coarse particles for the winter-spring period is only different from other seasons and fine particles. We will discuss possible explanations of this different isotope pattern for the winter and spring periods.