DEVELOPMENT OF A LOW CUTPOINT SLIT VIRTUAL IMPACTOR FOR SAMPLING AMBIENT FINE PARTICLES

This paper presents the development of a small cut-off size slit-nozzle virtual impactor that operates at a small pressure drop. Operating with a preselective inlet that removes particles larger than 2.5 mu m in aerodynamic size, the impactor can sample ambient particles in the accumulation range (0.1<d(p)<2.5 mu m) In addition, a detailed measurement of the particle losses through the system is presented. The length of the impactor can vary according to the flow rate that is desirable. Different design configurations were tested to optimize the classification characteristics of the impactor. The ultimate goal was to minimize the impactor's cutpoint and the particle losses. The impactor was characterized using fluorescent monodisperse particles. It was demonstrated that the impactor has a 50% cutpoint in the range 0.1-0.25 mu m, depending on the configuration tested.