Fundamental Study on Control of Atmospheric Environment by Vegetation

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NO and NO2 fluxes were measured micrometeorologically from Oct.to Dec.in 1994 above vegetation and from Jul.to Oct.in 1995 above vegetation and bare soil. The experimental sites were a lawn (Zoysia matrella Merr.) trimmed to 1 cm (average LAI 4,2) and uncultivated bare soil, in Osaka Prefecture University. The fluxes were determined using a gradient method, together with those of CO2 and water vapor. Data for calculation were obtained near the surfaces, at heights of 2 and 8 cm. NO and NO2 concentration of the air sampled in shaded Teflon bags was determined with a chemiluminescent analyzer in a laboratory. The direction of NO flux was upward above both the lawn and bare soil in many cases. The NO flux changed seasonally from -0.1 -0.3 mgN m^<-2>h^<-1> in Jul.to -0.1 -0.1 mgN m^<-2>h^<-1> in Oct. The direction of NO2 flux was almost downward above the lawn, while that above the bare soil was uncertain. Above the lawn, negative correlations between the flux and concentration were recognized. The NO2 deposition velocity on the lawn decreased from about 0.4cm s^<-1> in Jul.to 0.1 cm s^<-1> in Dec. This was probably caused by the seasonal change in NO2 absorption through stomata.