A HIGH-VOLUME SMALL CUTPOINT VIRTUAL IMPACTOR FOR SEPARATION OF ATMOSPHERIC PARTICULATE FROM GASEOUS-POLLUTANTS

This paper discusses the development of an alternative technology to s ample separately the gas and particulate phases of atmospheric polluta nts. The key feature of this technique is the utilization of a slit no zzle virtual impactor with a small 50% cutpoint (0.1 mu m) to sample a tmospheric pollutants at high flow rates (225 LPM). In contrast to the diffusion denuder/filter pack and impactor/filter pack techniques, wh ich collect gas and particulate phases sequentially, the two phases ar e separated in a virtual impactor and collected independently, to elim inate sampling artifacts. The virtual impactor has been characterized in laboratory studies using fluorescent monodisperse aerosols, and in field studies by comparing its performance to the performance of a col located dichotomous sampler. The results indicate that the minor flow (consisting of particles in the range O.l<d(p)<2.5 mu m) flow of the v irtual impactor contained on the average 80% of the total ambient fine mass. In addition, particle losses range from 5 to 15%, and tend to s lightly increase with particle size.