Fine particle dry deposition onto a cropland - A trial to estimate deposition velocity

The dry deposition velocity of fine particles is usually on the order of se veral tenths of cm s(-1), and accordingly, the concentration gradient of pa rticles above the surface is very small. This makes the application of the gradient method to the determination of the particle deposition velocity ve ry difficult. This study is a trial to find a way around this difficulty. T he idea is to evaluate the thickness of the molecular diffusion layer, zb b y simultaneously measuring the concentration gradient of gaseous species su ch as SO2; zb is obtained by combining the turbulent and molecular transpor t equations for the gas. Then the particle deposition velocity is estimated oil the basis of zb and the Brownian diffusion coefficient with an assumpt ion that zb is equal to the thickness of the Brownian diffusion layer. By a pplying this method to the data collected in a field observation, the veloc ity of deposition onto a cropland was estimated for submicron particles.