Transport of SO2 Gas to Grass

Abstract

The vertical flux of SO2 gas above the grass was calculated by the aero-dynamic method. If the flux F is assumed to be constant with height, F can be expressed asF=-(ρ1-ρ2)/∫Z1Z2-1/KdZ (1)where ρ1 and ρ2 are the concentrations of SO2 gas at heights z1 and z2 respectively above the grass and K is the turbulent transfer coefficient. In order to calculate the value of F from eq. (1), simultaneous measurements were carried out of both profiles of wind velocity and air temperature and of the concentrations of SO2 at 200cm and the surface of grass with mean height of 50cm. The concentrations of SO2 gas at two levels were recorded continuously with two SO2-meters. The turbulent transfer coefficient was determined by the formula for non-neutral condition, using both profiles of wind and air temperature.When the wind direction shifted to that of an iron-foundry, an increase in the concentration of SO2 gas was observed. On this occation the concentration of SO2 gas at 200cm exceeded that at the grass aurface. Differences in concentration between the two levels ranged from 0.02 to 0.08ppm. The calculated value of F incresed with wind speed and varied from 2×10-10 to 15×10-10g/cm2/sec.From the values of F and SO2 concentration at 200cm, the velocity of deposition defined as Vg=F/ρ by Chamberlain (1953) was obtained. Under the condition of the measurements Vg had a range of 0.5-4.0cm/s and showed an obvious increasing tendency with wind speed (Fig. 2). The obtained values of Vg were the same order of magnitude as those of Chamberlain (1953) for the vapour of Iodine 131 above grass. No significant difference was observed between the dependence of Vg on wind speed at night and that during daytime. Consequently it seemed that the contribution of stomatal absorption of SO2 gas to the velocity of deposition was likely to be unimportant.