Abstract
The Semi-Active Sampler (SAS), which has been developed by our group, is a new type of gas sampler composed of a cylindrical metal housing in which the coaxial rods of the diffusion layer and the adsorbent layer. Air flow in the gap between the housing and the diffusion layer can be induced by a small fan equipped inside the sampler. The sample air can be introduced to the sampler by the forced convection inside the sampler. The target VOC components in the sampled air can be collected by the diffusion through the diffusion layer and be captured by the adsorbent. The transport process of the VOC components in the SAS was modeled based on the film theory, and it was found that the sampling rate of the SAS is a linear function of the-1/3 power of the air flow rate of air in the SAS. The above dependency agreed well with the experimental results for toluene, ethylbenzene, and xylene. The sampling rate found to depend on the 1/3 power of the representative diameter (the difference of the housing diameter and the passive sampler), which agreed with the experimental results. The effect of the outer air flow rate on the air flow inside SAS was studied, and found that the sampling rate was almost unaffected by the change of the outer air flow rate up to 4 m/s.
