Synthesized measurements of reactive nitrogen fluxes onto a forest using gradient and relaxed eddy accumulation method

Kazuhide Matsuda1, Takaaki Honjo1, Mao Xu1, Taiichi Sakamoto1

1 Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan,

Email (K. Matsuda)


Synthesized measurements of vertical profiles and exchange fluxes of reactive nitrogen and relevant species, which are fine (PM2.5) and course aerosol components (NO3 , NH4+ SO42-) and gas components (HNO3, NH3, SO2), were carried out in a deciduous forest, suburban Tokyo.  Average vertical profiles in daytime and nighttime during the experiment showed the down ward fluxes (depositions). Differences of decreasing rates among the components were approximately in accordance with theoretical deposition velocities, except NO3 in PM2.5. Decreasing ratio of NO3 in PM2.5 from upper to lower canopy was significantly larger than that of SO42- in PM2.5 or NO3 in coarse aerosols. From the measurements by relaxed eddy accumulation, deposition velocities of NO3 in PM2.5 were larger than those of SO42- in PM2.5. The large deposition velocity was possibly caused by an effect of shifts in equilibrium between aerosol phase (NH4NO3) and gas phase (HNO3, NH3) near surfaces. It was indicated that NH4NO3 could be quickly removed as well as HNO3 in some conditions.