The transport of fine particulate and gaseous matters in gas flow due to convection and diffusion is investigated by measuring the change in concentration of submicron particles as well as oxygen when introduced into a 12l chamber. To calculate the concentration change, the NavierStokes and convection-diffusion equations are solved numerically. A finer computational grid is necessary to predict the concentration of particles which have very small diffusivities. The calculations agree well with the measured concentration changes at the outlet of the chamber and can quantitatively predict both the dependence of concentration on flow rate and the difference between the particles and oxygen. The transport of the particles is found to be governed solely by flow in the chamber, and the transport of oxygen which has a much larger diffusivity than the particles is also affected by diffusion.
Atmospheric particles and gases were collected with a low-volume sampler for every two weeks over the period from June 1991 to February 1992 in order to determine the variation of concentrations for particulate and gaseous Cl, Br and I in Chiba city. The contributions of resuspended soil particles to the content of the atmospheric particulate Cl, Br and I were negligibly small, based on the EF value which was defined as EFx=(X/Al)particle /(X/Al)soil. Particulate Cl and Br concentrations over the period from October to February were higher than those from June to September, whereas the variation in gaseous Cl and Br concentrations from June to February was small. Particulate I concentrations over the period from October to February were higher than those from June to September, whereas gaseous I concentrations showed the inverse seasonal variations. Thus, the concentration of particulate I seems to be complementary with that of gaseous I in the atmosphere. In addition, the clear correlation was observed between the atmospheric temperature during the each observation period and the gas-particle distribution factor of I [f(I)] which was defined as f(I)=P(I)/[P(I) + G(I)]. Here, P(I) and G(I) are the concentrations of particulate and gaseous I, respectively. It is strongly suggested that the gas-particle conversion of I is dependent on temperature, therefore that would be the reason of the observed complementary seasonal variation of I concentrations in the particulate and gaseous phase.